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ESSL LAR 2008: Strategic Goal #5, Priority #2

Earth and Sun Systems Laboratory endeavors are central to NCAR's Strategic Goal #5, to "Provide world-class ground, airborne, and space-borne observational facilities and services." This Strategic Goal includes three Strategic Priorities, two of which are closely tied to work by ESSL staff.

Goal #5, Priority #2, Developing new instrumentation, is described in the NCAR Strategic Plan as follows: "Advances in research on weather, climate, the water cycle, chemistry and dynamics of the upper troposphere/lower stratosphere, space weather and solar physics, and biogeosciences all require capabilities that stretch beyond those provided by (NCAR's) current suite of airborne and ground-based instruments. NCAR is tasked with developing a new generation of robust, inexpensive, easily deployable, and versatile instrument systems to address the university community's need for these instruments, which facilitate their research efforts. Our extensive and talented scientific and engineering staff continually creates and test new instrumentation for studying the links between atmospheric composition and the biogeosciences, with systems for quantifying the surface-atmosphere exchange of gases and aerosols on whole-plant, whole-canopy, and regional scales using mobile laboratories and research aircraft."

Significant efforts by scientists and staff of the Earth and Sun Systems Laboratory (ESSL) are focused on addressing this Priority in order to provide the observations necessary for improved understanding of the Earth and Sun Systems.

The section below describes specific research conducted by ESSL staff under projects relevant to Goal #5, Priority # 2. The major ESSL activities in this area include development of chemical instruments for HIAPER, development of a Coronal Solar Magnetism Observatory (COSMO) and instruments for the Solar Dynamics Observatory, continued use and evaluation of satellite measurements from the HIRDLS and MOPITT instruments, development of airborne and ground-based chemical and meteorological instrumentation, and development of a Satellite Observation Simulator and Assimilation System (SOSAS).

  1. Development of a COronal Solar Magnetism Observatory (COSMO) - HAO
  2. High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) instrumentation - ACD
  3. Analysis of data from Hinode and STEREO - HAO
  5. Measurements of Pollution in the Troposphere (MOPITT) - ACD
  6. Atmospheric chemistry instrumentation - ACD
  7. Community Spectro-Polarimetric Analysis Center (CSAC) - HAO
  8. Instrument and experimental meteorology - MMM
  9. Development of instrumentation for the Solar Dynamics Observatory (SDO) - HAO
  10. Fundamental physics of radiative processes - HAO
  11. Virtual remote sensing facility - ACD
  12. Analysis of data from TIMED and COSMIC - HAO
  13. Development of the Sunrise balloon mission - HAO

Development of a COronal Solar Magnetism Observatory (COSMO)

Figure 1: Concept drawing of the COSMO 1.5-meter coronagraph and dome. The telescope is a simple tube structure on an equatorial mount. The diameter of the dome is 12.2 meters.

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Driven by society's need to understand the origins of space weather, NCAR scientists at the High Altitude Observatory, along with colleagues at the University of Hawaii and the University of Michigan, plan to build the Coronal Solar Magnetism Observatory (COSMO). The facility will take continuous synoptic measurements of the entire corona in order to understand solar eruptive events that drive space weather and to investigate long-term and solar-cycle phenomena. The primary instrument will consist of a 1.5-m coronagraph with two detector systems: a narrow-band filter polarimeter and a spectropolarimeter. Supporting instruments are a white-light coronagraph to record the evolution of the electron scattered corona (K-corona) and a chromosphere and prominence magnetometer. This new facility will replace the current NCAR Mauna Loa Solar Observatory which has been collecting synoptic coronal data for over 40 years in support of the solar and heliospheric community.

In order to demonstrate the feasibility of measuring coronal magnetic fields, prototype instruments have been developed over the past 5 years at NCAR and the University of Hawaii. The Coronal Multi-channel Polarimeter (CoMP) instrument is a prototype of the COSMO coronal magnetometer which was built at NCAR/HAO. Last year, the CoMP enabled a scientific breakthrough by imaging, for the first time, Alfven waves in the solar corona. These waves were found in observations of the Doppler-shift of coronal plasma in the Fe XIII emission line at 1074.7 nm. These waves are important in that they transport energy from the turbulent photosphere out into the solar corona, and could explain why the solar corona is heated to a temperature of 1 million degrees. In 2008, we exploited the fact that the speed of propagation of these waves depends on the magnetic field of the corona. This allows us to use the wave speed measurements from CoMP to determine the strength of the coronal field. This effort is part of an exciting new field called Coronal Seismology.

In 2009, we will move CoMP from the NSO Sacramento Peak Observatory in New Mexico to the University of Hawaii's Mees Observatory atop Haleakala in Maui. This will allow us to obtain coronal observations under excellent sky conditions and fully exploit the scientific potential of the CoMP instrument.

Planning for COSMO has been assisted by a Scientific Advisory Panel of community members who have set the scientific requirements for the facility. Operation of the facility will continue to be guided by the Scientific Advisory Panel which will insure that the facility will continue to meet the needs of the solar and heliospheric community which it serves. The development of the CoMP instrument was supported by the NSF through the NCAR Strategic Initiative Fund and HAO base funds.

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High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) instrumentation

Figure 1. HARP rack installed on the NSF HIAPER GV aircraft, irradiance and actinic flux zenith and nadir optics.

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PI: Andrew Weinheimer (UCAR/NCAR) - completed FY2008

NO-NOy Instrument - Two-channel instrument for the in situ measurement of NO (nitric oxide) and NOy (total reactive nitrogen).

The CARI two-channel chemiluminescence instrument is capable of 1-sec in situ measurements of NO and NOy. The instrument was completed and certified for the GV early in FY2008, and was flown successfully on the NCAR/NSF GV aircraft during the START08 mission in April/May and June/July of 2008. The instrument worked very well and we collected a complete data set during the START08 mission, which will contribute to the characterization of stratosphere-troposphere exchange processes in mid-latitudes. Plans for FY2009 include some re-design of the inlet to optimize pressure control and minimize wall losses of nitric acid. This inlet design will also support the needs of the GA Tech CIMS HAIS instrument, which the CARI group expects to receive during FY2009. Some software changes and reprogramming are also planned to make the software more stable while communicating with GV the aircraft data systems. See the CARI group report for details on the NO/NOy instrument.

PI: Teresa Campos (UCAR/NCAR) - completed in FY2008

Fast Ozone Instrument - Quantification of ozone mixing ratios at 5 Hz using the method of chemiluminescent reaction of ozone with nitric oxide.

The Fast-Ozone instrument was completed and certified to fly on the GV in early FY2008. The instrument was then flown on the START08 mission, together with the NO/NOy instrument. Both systems used an integrated pumping system and shared the data system which was redeveloped to accommodate both instruments to save space and weight when deployed together on the GV. Laboratory tests as well as analysis of flight data confirmed that the time resolution of the fast-Ozone instrument is indeed 5 Hz or better. A complete data set was collected during the START08 mission and the ozone data compared extremely well with two additional ozone sensors flown during START08 and operated by NOAA.

PI: Eric Apel (UCAR/NCAR) - estimated completion: FY2009

Trace Organic Gas Analyzer (TOGA) - In situ measurements of oxygenated volatile organic compounds (OVOCs), non-methane hydrocarbons (NMHCs), and halocarbons.

The Trace Organic Gas Analyzer (TOGA) will be completed in FY 09. It will have the unique capability of simultaneously measuring, with one instrument, a suite of organic compounds that play important functions in many areas of atmospheric chemistry. Several of the compounds are precursors or intermediates in atmospheric oxidation sequences. Others are indicators or tracers of different anthropogenic and biogenic processes. The compounds that TOGA will measure consist of a series of hydrocarbons, oxygenated compounds, halocarbons (including HCFCs and CFCs), and a few nitrogen and sulfur containing compounds. These species are identified in the HIAPER Advisory Committee Report as high priority. A prototype of this instrument was flown successfully on the NASA DC-8 aircraft during the ARCTAS mission in March/April and June/July of 2008. Excellent data was collected during ARCTAS including quite possibly the first accurate data of acetaldehyde in clean air masses.

PI: Rick Shetter (UCAR/NCAR) Estimated Final Acceptance: FY2009

HIAPER Atmospheric Radiation Package (HARP) - Spectrally resolved actinic flux and stabilized platform irradiance measurements.

Rick Shetter and his Atmospheric Radiation Investigations and Measurements (ARIM) team, in collaboration with Peter Pilewskie and Bruce Kindel of the University of Colorado, Manfred Wendisch of the Leibniz-Institute for Tropospheric Research, Rainer Schmitt of Metcon, Inc and Dieter Schell of Enviscope GmbH, Germany, developed the HIAPER Airborne Radiation Package (HARP), a comprehensive atmospheric radiation suite to measure in situ actinic flux and irradiance. The ARIM group developed the actinic flux package using a CAFS detection and was responsible for building the spectrometer computer systems, creating the data acquisition and control software, coordinating the assembly of the racks, equipment, input optics and stabilized platforms, and leading the integration and flight management of the instrumentation.

The irradiance measurements rely on horizontal stabilization to determine layer properties, such as reflectance, transmittance and absorbance. Thus, the HARP irradiance package is mounted on zenith and nadir stabilized platforms to account for aircraft attitude changes. The platform was tested during the HIAPER Aircraft Instrumentation Solicitation Experimental Flight Test - 2008 (HEFT-08). The stabilized platform performed well and responded precisely to positional commands. However, the navigation signals used to determine aircraft attitude were inaccurate due to signal timing delays and noise on the signal line. To eliminate these external errors, the HARP system has been upgraded to receive direct GPS antenna signals. Final testing and delivery of the HARP instrumentation is forthcoming.

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Analysis of data from Hinode and STEREO

Figure 1: Fine structure of the solar chromosphere and a solar prominence are clearly visible in this image taken by Hinode. Time sequences of imaging data have revealed the presence of MHD waves in the upper atmosphere that may be the elusive source of heating the outer solar atmosphere and acceleration of the solar wind. This image is taken from an article by Okamaoto, et al. in the special Hinode issue of Science, 7 December 2008, p 1577.

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During FY2008 the Joint Japan/US/UK Hinode mission entered its second year of operation. Many new science results continue to pour from the analysis of Hinode data. HAO/ESSL/NCAR hosted the Second Hinode Science Meeting in Boulder the week of 28 September 2008, with an international participation of about 200 scientists. The theme of this meeting, "Beyond Discovery, Toward Understanding", emphasized detailed quantitative analysis and the integration of numerical models with observations. The Hinode team at HAO has contributed many new science developments over the past year, some of which are highlighted in this document under "Profiles in Science and Technology." Furthermore, HAO scientists were involved in many articles in the Special Issue of Science Magazine (7 December 2007) devoted to new results from Hinode. The Hinode mission has provided an avenue for many HAO scientists to open new scientific collaborations, including advising and collaborating with PhD students from other institutions.

HAO continues to contribute to mission operations and community access to Hinode data. Systematic data reduction of the now almost 2 years of Hinode science data from the Spectro-Polarimeter (SP) onboard Hinode is being carried out at NCAR. The complex analysis procedure for SP data was developed at HAO initially under the NCAR Strategic Initiative "Community Spectro-Polarimetric Analysis Center" (CSAC). Refinement and updates to this reduction software are ongoing as a contribution of HAO to the Hinode program. These fully calibrated "Level 1" SP data are then made available to the community via the internet. Through CSAC, HAO is also providing the SP "Level 2" data: a detailed analysis of the polarization spectra to provide maps of the magnetic field vector in the solar atmosphere. Bulk processing of SP Level 2 data began at HAO in FY2008, and is now being made available to the community. HAO scientists participated in Hinode mission operations that require them to travel to Japan to prepare the science operations plans.

HAO scientists, in collaboration with many other scientists worldwide, continue to use the Hinode observations in innovative ways. One such example is the high resolution Hinode image shown in Figure 1 that reveals the ultra-fine structure of the upper layers of the solar atmosphere (the chromosphere). Sequences of such images have led to new understanding regarding the dynamics of the solar atmosphere, how it is linked to the dynamics of the magnetic field below, and how waves propagating through this region might be the elusive source of the heating of the solar corona and acceleration of the solar wind.

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Figures 1 and 2. Comparisons of HIRDLS V4 ozone retrievals with ozone sonde data at the locations and dates indicated. Separation of the sonde and HIRDLS retrievals is 95 km and 2.5 hours for the May profile, and 238 km and 0 hours for the April profile. The HIRDLS retrievals (blue) pick up the fine vertical features seen by the sondes (black dots).

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Figure 2.

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The High Resolution Dynamics Limb Sounder (HIRDLS) is a 21 channel infrared limb scanning radiometer, jointly developed by ACD, the University of Colorado, and the Physics Department of Oxford University. It is designed to make observations of temperature, ozone, water vapor and 8 other trace species, as well as PSC's, aerosols and cirrus clouds, from the upper troposphere to the mesosphere, with higher vertical resolution than has previously been available from space observations. NASA funded the U.S. share of the HIRDLS development. When HIRDLS was launched on the Aura spacecraft in July 2004, a thin plastic film from inside HIRDLS came loose and obstructed most of the instrument's aperture, limiting the view to the atmosphere to a small fraction of the width of the optical beam. As described previously, the HIRDLS team, led by John Gille, the U.S. PI, and John Barnett (Oxford), the U.K. PI, showed that there was useful information in the signals. This required the development of 4 major adaptations and corrections to the measured signals. The first, revising the calibration, was described earlier.

The next steps were to correct the measured signals to make them as close as possible to the expected radiances. The major efforts this year were to complete the algorithms to remove the spurious oscillations (due to mechanical oscillations of the plastic), and to recalculate the pointing. In addition, critical improvements were made in the corrections for the partial viewing area, and the estimation and removal of the signal coming from the obstruction.

A key method for determining these corrections is to have the spacecraft pitch by ~5°, so that HIRDLS looks above the atmosphere and measures signals only from the plastic film. This year the ACD HIRDLS team coordinated 2 of these pitch maneuvers. The initial development of these algorithms was described previously, but work continued, especially to improve the estimate of the reduced viewing area, and to refine subtraction of the signal from the plastic film. The latter is the biggest difficulty at this time. Updated calibration coefficients, radiance sample geo-location, and improved cloud location had been incorporated in the operational processing code. The resulting processor version was run on all the observations to produce a data set designated internally version 2.04.09. These data include global profiles of temperature, ozone, nitric acid and aerosol/cirrus; it was released to the community as Version 3 (V3) data. These were publicly released at the beginning of the reporting period.

Subsequent improvements have resulted in a new processor, v2.04.19, and a new V4 data set that was released near the close of the reporting period. These data include profiles of CFC 11, CFC12, and aerosol extinction, as well as temperature and ozone that have improved accuracy and fewer data spikes. The HIRDLS temperatures are now in within 0.5K of U.K. Meteorological Office high-resolution radiosonde data for 9 widely distributed stations, and for all data available from January 2005 until August 2007, while continuing the 1 km vertical resolution obtained previously. HIRDLS temperature retrievals show the same very good agreement with high resolution radiosondes as the earlier version, shown in the last Annual Report. V4 ozone retrievals also show very good agreement with sonde data, and the ability to see small scale structure, as illustrated in Figures 1 and 2.

The NCAR HIRDLS team hosted members of the core Oxford team for a 2 day meeting in January to discuss data improvements and future plans. This was followed by an open meeting with community members to discuss and encourage the scientific applications of HIRDLS data. The team also presented their status and plans to a review team from NASA, and attended similar core team and open science meetings in Oxford in June.

After an increasing number of spikes in the chopper motor current beginning in January, the chopper ceased operating on 17 March. Considerable effort has gone into diagnosing the problem, and attempting to restart the chopper, so far without success.

In the next year the correction algorithms will be refined to allow the recovery of additional species such as water vapor and methane. Emphasis will be on improved estimation of the partial view area and especially of the signal from the plastic, including allowances for the variation of the latter with time. In parallel, emphasis will be placed on the use of the released data for scientific studies, especially of UT/LS processes and strat-trop exchange, but broadening to many other areas (See Goal 1 ).

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Measurements of Pollution in the Troposphere (MOPITT)

Figure 1. Monthly mean MOPITT CO total column results for March, 2006 based solely on near-infrared observations.

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MOPITT Operational Production of Carbon Monoxide Data

The daily operational processing of Measurement Of Pollution In The Troposphere (MOPITT) instrument raw counts into the final retrieved geophysical products, delivery of products to NASA for free public access, and user education and support, constitutes a major service to the scientific community. MOPITT is also unique in providing the community with the longest continuous validated global CO data product. Scientific results have been presented worldwide at numerous scientific meetings and show a documented strong presence on the Internet. MOPITT data distribution, publications, literature citations, and conference presentations are all showing strong upward trends, indicating mounting demand and scientific interest.

Development of new data processing software for the next product release, 'Version 4,' has just been completed. Major features of the new retrieval algorithm include: (1) a new forward model with improved description of the MOPITT gas correlation cells and applicability to a wider range of CO mixing ratios; (2) a new description of the retrieval a priori surface emissivity; (3) a new seasonally and geographically variable CO retrieval a priori; and (4) the use of an assumed log-normal variability for CO volume mixing ratio. The new product also includes more extensive diagnostics, including the retrieval averaging kernels.

Activities during FY08

Algorithm Development and Product Evaluation

The development of a substantially improved retrieval algorithm for processing the next major MOPITT data product ('Version 4') was recently finalized. Associated activities completed in FY08 included (1) enhancement of the operational radiative transfer model to reflect actual in-orbit instrumental parameters and to better handle extremely polluted atmospheres and (2) determination of appropriate radiance bias correction factors. Product evaluation activities included analysis of V4 results at validation sites where aircraft in-situ profiles and surface measurements are available throughout the mission (since 2000). Overall, validation results indicate very small retrieval biases at all levels and demonstrate significantly weaker long-term drift than was observed in the current MOPITT Version 3 Product.

Long-term goals for the MOPITT Team include the incorporation of MOPITT's near-infrared measurements (i.e., 'solar channels') to provide additional information with respect to the CO total column measurement. Neither the current MOPITT Version 3 product nor the upcoming Version 4 products exploit these measurements because of challenges in understanding apparent instrument noise specific to these channels. During FY08, however, MOPITT retrievals based on these measurements were demonstrated for the first time, and clearly indicate the promise of combined thermal-infrared/near-infrared (TIR/NIR) CO retrievals for future products. Figure 1 presents global monthly-mean CO total column retrievals based solely on MOPITT NIR measurements during March, 2006. Regions of biomass burning in Equatorial Africa as well as anthropogenic emissions in China (principally from fossil fuel burning) are both clearly evident in the figure. Compared to current retrievals based purely on TIR measurements, the new NIR retrieval product is more sensitive to CO in the boundary layer and therefore should be much more capable of identifying sources at the surface.

Reference: "CO retrievals based on MOPITT near-infrared observations," by M. N. Deeter, D. P. Edwards, J. C. Gille, and James R. Drummond, submitted to J. Geophys. Res.

Field Campaign Support

The NCAR MOPITT Team produced and provided near real-time imagery and CO data products to support the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) field campaign during Spring and Summer phases in FY08. Analyses of these data are ongoing.

Plans for FY09

Production and Release of V4

Operational processing of the MOPITT Version 4 product will begin in early FY09. The acquisition of new linux servers should allow processing of the entire MOPITT mission within several months, however the prerequisite task of porting all of the associated software to the new hardware may itself take several months. This process has begun. In preparation for the release of the new product, a new User's Guide is being drafted. Also, as the official release date approaches (possibly around the end of 2008), the new product will be publicized within the community. This effort will include a presentation at the Fall AGU meeting.

Version 5 Development

As operational processing of the Version 4 product becomes routine, initial steps to define and develop the Version 5 product will begin. While preliminary, current objectives for V5 development include the incorporation of MOPITT's solar channels and an evaluation of alternative sources for meteorological data.

Continued Analysis of Operational MOPITT Products

The MOPITT Science Team will continue to evaluate operational products both in the context of traditional validation (e.g., using available in-situ data from aircraft and ground-based spectroscopic measurements) and in comparison to models.

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Atmospheric chemistry instrumentation

Figure 1. The new, compact PAN-CIGARette instrument was used for fast (1-2 sec), continuous measurements of PAN and related species on the C-130 for the MIRAGE and INTEX-B programs.

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Figure 2. Zenith and nadir optics and instrument rack on the NASA DC-8 aircraft during ARCTAS.

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Figure 3. CAFS measured and TUV (clear sky) modeled j(NO2) during the ARCTAS/CARB deployment. The measurement/model differences are due to clouds and aerosol layers.

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ACD scientists are involved in ongoing efforts to develop, improve, operate, and maintain a number of instruments designed to measure trace gases, radicals, optical properties, and aerosols in the atmosphere.

CARI Instrumentation

Aside from the community chemistry instruments and HIAPER instruments the CARI Group maintains and continued to improve a four channel chemiluminescence (CL) instrument for the simultaneous measurement of NO, NO2, NOy, and Ozone with a time resolution of 1 second or better. This instrument can be configured to fly on a variety of aircraft such as the NCAR C-130, the NASA WB-57, the NASA DC-8, and others. It can be flown unattended or with an operator and was deployed successfully during the NASA led ARCTAS experiment in 2008. CARI also maintains a compact chemical ionization mass spectrometer (PAN-CIGARette, Figure 1) which measures PAN at up to 4 Hz frequency or a number of different PAN species at 0.5Hz or better depending on number of species. We are planning to add this instrument to the pool of community instruments maintained by CARI . The PAN CIGARette would then become requestable for use on the NCAR/NSF aircraft. Both the four channel CL and the PAN CIGARette will be deployed during the OASIS field mission planned for early 2009 in Barrow, AK.

Ultrafine Aerosols

During 2008 the Ultrafine Aerosols group developed new instruments to study the formation of atmospheric aerosols and their impacts on climate. An ion trap mass spectrometer was built by visiting German Research Foundation postdoc Andreas Held and interfaced with a redesigned electrostatic nanoparticle sampler for measuring nanoparticle chemical composition by the thermal desorption chemical ionization mass spectrometry (TDCIMS). Dr. Held also completed the design of a conditional sampling inlet which works with the TDCIMS to obtain size-resolved nanoparticle chemical flux. This instrument was deployed at Marshall Field Site and at the BEACHON Southern Rocky Mountain experimental site in 2008. Work continued on developing a scanning mobility particle sizer for the GV aircraft. Design of the instrument is nearing completion with the goal of flight testing the system in 2009. Finally, a hygroscopicity and volatility tandem differential mobility analyzer was designed and assembled that can measure size-resolved aerosol hygroscopic growth factors at 90% RH at user selectable residence times of 1, 2, 5 and 28 s as well as size-resolved aerosol volatility at user selectable temperatures from room temperature to 300 °C and at user selectable residence times of 0.8 and 10.5 s. This instrument operates autonomously and will be used in the 2009 OASIS field study in Barrow, AK.

Photochemical Oxidation and Products

In the Photochemical Oxidation and Products Group (POP), instrumentation for the measurement of HOx has been present in ACD since the late 1980s when an improved chemical amplifier was developed and deployed during MLOPEX II (1991-1992) (Cantrell et al., 1984; Cantrell et al., 1996). This instrument provided valuable information in this ground-based study. Follow-on studies saw further improvements. The presence of the NCAR chemical amplifier was instrumental in assessing the status of HOx measurements during the PRICE-I campaign in southern Germany. While useful, the chemical amplifier has a number of limitations. After MLOPEX II, Fred Eisele moved from the Georgia Institute of Technology bringing his mass spectrometric-based method for measurement of tropospheric OH and sulfuric acid (H2SO4) (Eisele et al., 1996). This enhancement to the measurement capability at NCAR also offered the opportunity to develop a new technique for quantification of peroxy radicals (HO2 and RO2). In addition, through internal and external support, the previous ground-based instrumentation was improved to allow deployment aboard aircraft platforms (Mauldin et al., 2001). Improvements continue with the development of smaller, lighter single channel OH and HO2 instruments, which were deployed during the recent NASA-sponsored ARCTAS campaign (spring & summer 2008). Currently, instrumentation for deployment on the NSF Gulfstream-V aircraft is under development, and University of Colorado graduate student, Josh McGrath, is developing a new tool to measure the reactivity of OH in the ambient troposphere. In the past, mass spectrometric-based instrumentation was used to measure DMSO and DMSO2 (DMS oxidation products, Nowak et al., 2002), HNO3 (Zondlo et al., 2003), and NH3.

Atmospheric Radiation Investigations and Measurements

The Atmospheric Radiation Investigations and Measurements (ARIM) group maintains Charged-coupled device Actinic Flux Spectroradiometers (CAFS) and Scanning Actinic Flux Spectroradiometers (SAFS) to measure up and down-welling wavelength dependent actinic flux in the UV and visible wavelengths. The measurements are based on a 2π steradian hemispherical zenith and nadir optical collectors coupled with UV enhanced fiber optic bundles to small, lightweight, monolithic CCD monochromators and double monochromator with photomultiplier tube detection, respectively. The instruments have an excellent record of performance on the NCAR HIAPER GV and C-130, the NASA DC-8, WB-57 and P-3B, the NOAA WP-3D and at numerous ground stations.

The ARIM optical calibration facility is equipped with precision radiometric power supplies and multiple NIST traceable 1000W quartz tungsten halogen lamps to determine the spectral response of each instrument. Secondary lamp standards are applied in the field. Mercury line calibrations are also performed to track the wavelength accuracy.


The 2008 ARCTAS (funded by NASA) mission investigated the transport and transformation of gases and aerosols affecting the Arctic. The winter phase was based in Fairbanks, AK, and explored the transport of pollution across the Arctic, with a focus on arctic haze, tropospheric ozone and surface deposited black carbon. The summer phase was based in Cold Lake, Alberta, and concentrated on the contribution of boreal fires to the atmospheric composition and climate of the Arctic region.

CAFS instruments were deployed on the NASA DC-8 aircraft for the full campaign to provide photolysis frequencies for the critical chemical constituents of the arctic. In particular, the photolysis contributes to the study of the evolution of pollution plumes and the tropospheric oxidant chemistry. Several factors specific to the arctic affected the actinic flux. The scattering in arctic haze tends to increase the flux while absorption in boreal fire emissions decreases the flux. Surface deposited black carbon also decreases the flux by reducing the surface albedo. Thus, the in situ measurements were critical to assessing the local radiation field.

Prior to the summer phase in Cold Lake, Alberta, the California Air Resources Board funded a series of flights based from the NASA Palmdale facility to study the dynamics of the transport of Asian pollution into California, local anthropogenic pollution and greenhouse gas emissions. Again, the actinic flux measurements were critical to understand the local chemistry and evolution of the emissions.

The extensive California wildfires were also studied. The actinic flux was often dramatically reduced within the fire plumes, slowing the photolysis chemistry.

The CAFS instruments were redesigned for DC-8 installation, including new instrument housings, PC-104 computers and electronics, and upgrades to the data acquisition and control software. Data coverage was near 100% for the entire mission.

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Community Spectro-Polarimetric Analysis Center (CSAC)

Figure 1: Results from a MERLIN inversion of Hinode data obtained on 11 December 2007 are shown. The continuum intensity showing the sunspots is at upper left. This active region shows a channel of (upper right)horizontal (inclination &126;90° lower right) magnetic flux running from lower left to upper right, corresponding to a filament in the chromosphere above. The fields are oriented roughly along the channel (field azimuth, lower left). These data suggest that the flux forming the filament results from the emergence of a rope of magnetic flux.

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The Community Spectro-Polarimetric Analysis Center (CSAC) Strategic Initiative was conceived to strengthen HAO's position in the rapidly growing spectro-polarimetry community and also to transfer its 30+ years of heritage and leadership in the field to the broader community. CSAC is providing support for a host of new instruments for measuring vector magnetic fields in a range of solar atmospheric layers. Its most significant contribution to the broader community is the development and distribution of a modular suite of "standardized" (numerically robust, accessible, well-documented, and portable) computer analysis and data visualization codes that will be applicable to past and future spectro-polarimetric instrumentation.

During FY08 CSAC implemented the MERLIN (Milne-Eddington gRid Inversion Network) code as the workhorse analysis tool for data from the SOT/SP instrument on board of the Japan/US/UK Hinode spacecraft. These data receive the highest visibility and usage in the solar community. MERLIN output for SOT/SP is now being released through the CSAC web client. In FY2008 CSAC also begun standardizing the next-generation analysis tool LILIA (LTE Inversion based on the Lorien Iterative Algorithm) which will allows users to derive more detailed information about physical conditions in three dimensions within the Sun's magnetic photosphere by utilizing a more realistic atmospheric model.

In addition, work has begun on development of CAZAM (CSAC AZimuth AMbiguity utility), to visualize the vector magnetic field information produced by these codes. Current User Group: The CSAC user group currently consists of researchers from twenty institutes across the world.

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Instrument and experimental meteorology

Figure: Effect of shattering of large ice on the slopes of particle size distributions derived in ice cloud layers from several field programs. The uncorrected slopes have been shown to level off at about 9 cm-1 from many field programs (y axis). By removing shattering events from particle interarrival times, corrected values of the slopes have been obtained (x axis). It is noted that in fact the slopes continue to diminish (x axis) to as low as 4 cm-1. This shows that physical processes such as collisional breakup of large aggregates as has been theorized based on the earlier measurements is not a valid explanation for the earlier results but that shattering of large ice is.

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A central issue in the cloud physics community is the recognition that after three decades of measurements of particle size distributions we are not yet able to accurately measure the concentrations of ice crystals in clouds. The cause of these overestimates is shattering of large particles that impact the leading edge of the probes, with the resulting fragments passing through the probe’s inlets and being sensed as real particles. Overestimates of ice concentrations lead to smaller, more slowly falling crystals that do not sublimate readily in climate models in the middle troposphere through to the lower stratosphere and in these models ice-cloud albedos are significantly overestimated. This can result in major errors in the earth’s net radiation budget that requires other non-physical model changes to correct.

In an to attempt to rectify deficiencies in the measurement of ice crystal concentrations, we wrote an article this year that has pointed to errors in past interpretations of ice-particle-growth processes as a result of the shattering issue. Measurements of particle-size distributions (PSD) over more than two decades have shown that the slopes of exponential functions used to represent ice PSD’s in deep stratiform cloud layers reach a lower limit and then remain there. By correcting ice PSD for shattering based on measurements of particle interarrival times, this article shows that the reason why this lower limit was reached was due to shattering. Large particles impacting the leading edges of 2D imaging probes shattered, producing small particles. Broad size distributions, therefore, produced anomalous (shattered) numbers of small ones, maintaining the slopes at this lower limit. By removing the artifacts, this lower limit disappears (see figure).

Our efforts to understand and characterize ice PSD’s have extended to particles 50 microns and below, an area particularly troublesome to measure. We have acquired a new type of probe that has been designed to reduce known problems with the earlier probes. The small ice detector (SID-2) probe, an open path instrument that sizes in the range 1 to 60 microns, flew on the NCAR C130 aircraft during the Ice in Clouds Experiment (ICE-L [layer]) in November and December 2007. The ICE-L research flights included repeated penetrations through mountain-induced lenticular clouds. Three other probes that were designed to remove the shattering problem were deployed in the experiment. We have developed new knowledge on the presence and amount of small ice particles in clouds from these measurements.

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Development of Instrumentation for the Solar Dynamics Observatory (SDO)

Figure 1: Engineering drawing of the HMI Instrument. Light enters through the primary lens at the lower left and is images on the CCD cameras (light green, upper left). Click high resolution image for image with part names.

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The Helioseismic and Magnetic Imager (HMI) is one of the primary instruments to be flown on board NASA's Solar Dynamics Observatory spacecraft which will launch in June 2009 or January 2010. The HMI will record images of the Sun with 4096 by 4096 pixel detectors in wavelengths around the Fe spectrum line at 617.3 nm in various polarization states. These will allow us to construct images of the velocity and magnetic field over the entire solar surface with a spatial resolution of 2 arcseconds at a cadence of 90 seconds. The instrument development is led by researchers at Stanford University and the instrument is being constructed at Lockheed Martin. The construction phase was completed in 2008 and the instrument is now undergoing final testing at NASA's Goddard Space Flight Facility. Our role at HAO is to assist with the calibration of the instrument and to develop tools to convert the observations into physical parameters, such as the magnetic field strength and orientation. One challenging aspect will be to analyze the enormous volume of data in real time. In 2008, we completed the development of a computer code VFISV (Very Fast Inversion of the Stokes Vector) which can determine magnetic field parameters from polarization measurements significantly faster than any previous code. This code is now being incorporated into the HMI processing pipeline and is available for use by the community through the NCAR sponsored Community Spectro-Polarimetric Analysis Center (CSAC).

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Fundamental Physics of Radiative Processes

Figure 1: Convective patterns in a simulation of solar convection. Shown are (a) the radial velocity (b) the radial vorticity, (c) the horizontal divergence and (d) the temperature perturbation near the outer surface.

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Figure 1: The ProMag Calibration linear solver uses a 4-point calibration sequence of the form αΡ(i) = (i — 1)&deltaΡ and αR(i) = (i = 1, 2, 3, 4), where αΡ and αR are the positions of the calibration polarizer and retarder, repectively. The figure shows contour plots of the calibration success rate (above 90%) on the (&deltaΡ, δR) plane, for the three wavelengths of operation of ProMag (left to right: 587.6 nm, 635.3 nm 1083.0 nm). We see that, for ProMagsís specific design, there is a restricted set of optimal step pairs that maximize the success rate of the calibration procedure.

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Almost everything we know about the Sun comes from our interpretation of its radiative output. The study of the intensity and polarization of the radiation that we receive from solar regions allows us to infer the thermo-dynamical and magnetic properties of the emitting plasma, if we are able to formulate adequate models of the origin and transport of polarized radiation in the solar atmosphere. In the deeper and denser layers of the visible atmosphere (photosphere), plasma collisions typically ensure that, at each point in the plasma, the ratio of radiation emissivity to absorptivity (source function) is only determined by the local thermal properties of the plasma (local thermodynamic equilibrium, or LTE). Under these special conditions, the mechanisms for the production and transport of polarized radiation are very well understood, and reliable models have been available for at least half a century.

As we move outward in the solar atmosphere (chromosphere and corona), the plasma density rapidly decreases, while at the same time the radiation becomes increasingly anisotropic. Both conditions determine significant departures from LTE, as the atomic equilibrium is now driven mainly by optical pumping by the underlying photospheric radiation. These are also the regions of the solar atmosphere where the topology of the magnetic fields that permeate the heliosphere - finally interacting with the Earth's magnetosphere - takes shape. So the development of adequate models of polarized radiative transfer in these regions, in order to determine the correct magnetic boundary conditions of the heliosphere, is of primary importance for our understanding of solar drivers of Space Weather.

*FY08 achievements*

  1. R. Casini and M. Landi Degl'Innocenti and M. Landolfi (both of the Observatorio Atrofisico di Arcetri, Italy) resumed work on the derivation of a higher-order master equation for the description of atom+radiation evolution, based on a Feynman-diagram approach. The goal is to arrive at a self-consistent treatment of partial redistribution of photon frequency in the polarized scattering of radiation from complex atoms. This is a much needed advancement in order to achieve a full understanding of the many enigmatic polarization signatures observed in the solar spectrum. Progress in this long-term effort had come to a halt when Casini and collaborators were confronted with problems of non-conservation of probability in the atomic system. A delicate point in the derivation of the formalism is in the handling of the (unknown) initial conditions. In the past, this has been dealt with by resorting to heuristic arguments. This recent work has shown instead that it is possible to remove all references to the initial conditions in a systematic way. In the process, new terms appear in the formalism, which had not been considered before. Casini and co-workers have also initiated a systematic study of the implications of partial resummation of self-energy diagrams, through Dyson's equation, for the non-unitarity of the S-matrix in this type of radiation problems. The goal is to see if weak non-unitarity can be tolerated without compromising the correct physical picture of coherent radiation scattering.
  2. Casini worked on the creation of a calibration package for the Prominence Magnetometer (ProMag). A linear solver was built that can work on a restricted set of configurations of the calibration optics, optimized for the specific optical characteristics of ProMag's polarimeter. Numerical tests have shown that the linear solver gives stable, reproducible results in the determination of the polarimeter matrix. This linear approach is going to be much faster than typical non-linear optimization schemes applied to a redundant set of calibration configurations. The code has also been tested during the laboratory characterization of ProMag, and it has been instrumental to identify design and assembly issues with the polarimeter. Because of the ensuing delay in the field deployment of ProMag at the NSO Evans Coronal Facility, unfortunately the code has not yet been tested on real solar data from that telescope.

*FY09 plans**

  1. To progress on the theory of the polarized line formation in the presence of coherent scattering (partial redistribution in frequency), by evaluating the newly found terms, and by assessing the significance of the identified problems of non-unitarity of the S-matrix for the description of radiation processes in a dressed atom.
  2. To devise plasma diagnostic techniques exploiting the polarization effects of micro-turbulent electric fields on hydrogen lines (e.g., the role of electric-induced dichroism in optically thick plasmas), and to apply them to the joint determination of vector magnetic fields and plasma density in solar regions. (Collaborators: Rafael Manso Sainz, Arturo Lopez Ariste. Instituto de Astrofisica de Canarias.)
  3. To start the rewriting of the HANLE codes for scattering polarization in the chromosphere and corona to modern software standards, within the effort of the NCAR-funded Community Spectro-polarimetric Analysis Center (CSAC) strategic initiative.

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Virtual remote sensing facility

Figure 1. ACRESP Activities are grouped in two main areas: Satellite instrument design and future mission planning for atmospheric composition and air quality, and chemical weather forecasting, satellite data assimilation and field campaign support.

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Figure 2. The OSSE framework comprises the following key elements: (1) a science-driven requirement for a chemical species observation, (2) a satellite instrument simulator and observing strategy that might be capable of making a useful measurement, (3) a simulated data retrieval of the species with "nature" defined by an appropriate chemical transport Model 1, (4) a forecast of the species distribution using an assimilation of the retrieval in the "distorted" model 2, and (5) a quantitative assessment of the value of the measurement.

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Figure 3. WRF-Chem and MOZART simulated change in surface ozone (Maximum change for May 3-10) over Washington State with changes in Asian emissions.

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Figure 4. An example of the success of the ARCTAS chemical forecasts in predicting pollution plumes subsequently confirmed by aircraft measurements.

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ACRESP activities build on our current satellite missions and our expertise and leadership in satellite remote sensing science, Earth System modeling, and data assimilation. Recent advances in tropospheric remote sensing have opened the way for measuring, monitoring, and understanding processes that lead to atmospheric pollution. As part of an integrated observing strategy, satellite measurements provide a context for localized observations and help to extend these observations to continental and global scales. The challenge for future space-borne missions will be directly accessing the local scale and facilitating the use of remotely sensed information for improving local- and regional-scale air quality (AQ) forecasts. Achieving this goal will provide important societal dividends for public health, for policy applications related to managing national AQ, and for assessing the impact of daily human activity on the distributions of important trace gases and aerosols and their short-timescale variability - known as "chemical weather" - as well as on climate.

Satellite Instrument Design:

If a satellite mission related to atmospheric composition and air quality is to become a reality within the next decade, the atmospheric chemistry community will need to establish clear scientific motivation for the new measurements. For this, there is considerable interest in using chemical observing system simulation experiment (OSSE) studies to help define quantitative measurement requirements for satellite missions and to evaluate the expected performance of proposed observing strategies. These experiments will hopefully provide a practical way of defining a traceability matrix to map science requirements through measurement requirements onto instrument requirements.

OSSEs must be driven by well-defined scientific questions and the experiment formulation constructed accordingly. We have completed an example OSSE motivated by the desire to measure the distribution and time evolution of carbon monoxide in the lower-most troposphere for air quality applications using candidate satellite multispectral measurements in the thermal and near infrared.

Future Satellite Missions:

The ACRESP group is involved in the planning of The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission that has been recommended for launch in the 2013-2016 time frame by the National Research Council. The mission's purpose is to gather science that identifies human versus natural sources of aerosols and ozone precursors, tracks air pollution transport, and studies the dynamics of coastal ecosystems, river plumes and tidal fronts. Continuous observation from GEO-CAPE's geostationary platform will allow for more adequate monitoring of population exposure and the ability to relate pollutant concentrations to their sources or transport, thereby providing data to improve air quality forecasts.

ACRESP is a partner on a carbon monoxide instrument, the Compact Imaging Spectroradiometer (CISR), that builds on MOPITT experience and that has been specifically designed for geostationary deployment. CISR is candidate technology for GEO-CAPE and is currently under development as part of the NASA Instrument Incubator Program (IIP).

A longer-term goal of the ACRESP OSSE activity is to develop a community facility at NCAR. This would be used by researchers from the universities and agency centers for building and testing instrument simulators as part of the proposal and design of the next generation of satellite instruments.

Air Quality "Chemical Weather" Forecasting:

The Chemical Weather: Local, regional, and global distributions of important trace gases and aerosols and their variation on time scales of minutes to hours to days, particularly in light of their various impacts, such as on human health, ecosystems, the meteorological weather, and climate. (Lawrence et al., Environ. Chem. 2005, 2, 6-8, doi:10.1071/EN05014)

The ACRESP Program is developing an air quality "chemical weather" forecasting capability based on existing satellite observations. Chemical weather is a priority research theme for ESSL. The characterization of global and regional scale air quality involves field campaigns, chemical transport modeling, and remote sensing. The goal is a scientific and observing framework analogous to that used for weather forecasting with a model assimilation of observations from satellite, aircraft and surface platforms to derive a 4-dimensional view (3 spatial plus temporal) of the physical state of the atmosphere.

This analysis will be used in air quality basic research: the quantification of emissions of ozone and aerosol precursors and the examination of the long-range transport of pollutants extending from regional to global scales. The general tools and methodologies developed will also be used for studies examining the connections between climate change and regional air quality, and the roles of anthropogenic and natural processes in changing atmospheric composition. The predictive capability will provide a powerful tool to support field campaign activities such as those involving HAIPER chemical instrumentation. There also exists the possibility of demonstrating schemes for future operational applications elsewhere in the community related to air quality management and health advisories.

Increasingly, there is interest in accessing finer spatial scales to quantify both the wider impact of local pollution sources such as wildfires and mega-cities and assessing the contribution of transported pollution. We are conducting a chemical weather case study for the MIRAGE and INTEX-B spring 2006 period. This involves global model simulations using analyzed meteorology and the best possible chemical sources with fire emissions based on satellite fire products. A nested regional model simulation concentrating on Mexico and parts of the INTEX-B Pacific region are also being performed using WRF-Chem.

One of the open questions in AQ policy management is to what degree Asian industrialization and the associated transpacific transport of pollution could hinder improvements in AQ in the US from domestic emission controls. We have used the data set collected during the April/May 2006 phase of INTEX-B to look into the impacts of the long-range transport of pollutants across the Pacific on the U.S. West Coast. The study used global model simulations with altered Asian emission scenarios as boundary conditions for WRF-Chem simulations to examine the changes in concentration fields in both the global and the regional model. In another study, we focused on a direct application to AQ and quantified the impact of the fires in California in fall 2007 on regional air quality and especially on surface ozone by analyzing surface observations of ozone concentrations together with model simulations. It was found that the frequency of violations in the public health standards nearly tripled because of the fires.

Assimilation of available satellite data sets such as Terra/Aqua/MODIS aerosol optical depth, ENVISAT/SCIAMACHY and Aura/OMI NO2, OMI O3 tropospheric column, and Terra/MOPITT, Aura/TES, and METOP/IASI CO and O3 are being explored. This exercise will impose constraints on the modeled chemical fields and can be evaluated by compaing with actual field measurements. We have been working on a pre-cursor study with idealized satellite retrievals to examine the benefits and shortcomings in the assimilation of chemically active species. Largest improvements in predicting surface ozone were found when O3 or also NO2 fields throughout the atmosphere are available with high temporal resolution (3hrs) and for the online inversion of NO emission. However, the latter had the tendency for increasing biases in outflow regions. Work is ongoing on the assimilation of concentrations fields on a daily basis.

These projects involve the collaborative efforts between ACD and the DART initiative in IMAGe. We will also aim to foster collaboration with other efforts in the development of chemical weather forecast capability both within U.S. Universities, NOAA and NASA, and internationally, particularly with the GEMS project ( ) in Europe.

Field Campaign Support and Data Analysis:

ACRESP supported the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign with a combination of model simulations and satellite observations. Measurements were made from the NASA DC8 aircraft in the Spring and Summer of 2008, and were coordinated with several other field experiments as part of the International Polar Year (IPY). The Spring Phase of ARCTAS was April 1-19, based in Fairbanks, AK, and the Summer Phase was in Cold Lake, Alberta, June 26-July 14. In addition, several DC8 flights were made from Palmdale, CA, June 18-24, in coordination with the California Air Resources Board (CARB).

Retrievals of carbon monoxide (CO) from observations by Terra/MOPITT were produced in near-real-time. Chemical forecasts were produced using Ensemble Kalman Filter Data Assimilation of meteorological observations, MOPITT CO, and MODIS aerosol optical depth (AOD) with the NCAR Community Atmosphere Model with Chemistry (CAM-Chem). The data assimilation was performed in the Data Assimilation Research Testbed (DART) framework. Forecasts were also run with MOZART-4 driven by NCEP/GFS meteorology. The satellite retrievals and chemical forecasts were used to assist in the planning of the DC8 flights during the campaign by identifying features of interest for the aircraft to sample, such as pollution plumes from fires in Siberia and Canada.

Analysis of the ARCTAS measurements will continue in the coming year using a combination of satellite and model simulations. The assimilation of MOPITT CO and MODIS AOD in CAM-Chem/DART will be refined and evaluated with the aircraft observations, and, in turn, used to assist in the interpretation of the observations. Discrepancies between the model and observations will be used to improve the model and the emissions used to drive the model.

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Analysis of data from TIMED and COSMIC

Figure 1: Comparison of longitudinal variations of the F2 layer peak height in km (top) and magnetic meridional winds in m/s, positive equatorward (bottom), as a function of local time at 40° N during winter. Left: measurements by the COSMIC mission. Right: model results from the NCAR TIE-GCM.

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Figure 2: Development of the Weddell Sea ionization anomaly during southern hemisphere summer as seen in these constant-local-time plots of COSMIC data. The peak density of the F2 region of the ionosphere exhibits a possible connection to the equatorial ionization anomaly.

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Figure 3: Ionospheric electron content integrated between (a) 100-500 km altitude range and (b) 300-350 km altitude range of the COSMIC electron density observation at 2000-2200 local time during September equinox, 2006. 1 TECu = 1012 electrons/cm2.

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HAO conducts data analysis activities for several space-based observing missions, and uses the results to validate and improve models of the upper atmosphere and magnetosphere. One of the most important new activities is analysis of ionospheric results from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission, also known as FORMOSAT-3, which is a partnership between the U.S. and Taiwan and is managed by the University Corporation for Atmospheric Research.

HAO scientists and colleagues at National Central University in Taiwan have conducted several studies using data from COSMIC in the past year. Initial work during the first year of the mission focused on data validation and climatology, but during the second year, with the constellation fully deployed and dispersed, it has been possible to explore ionospheric phenomena, and to measure other quantities such as thermospheric neutral winds near 250 km altitude. This is done by measuring the effect of winds on the height of the maximum of the main ionospheric layer, the F2 peak. A study by Luan and Solomon [2008] compared peak heights and inferred meridional winds measured by COSMIC to simulations by the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), demonstrating the longitudinal variation of the wind pattern, controlled by the declination of the geomagnetic field (figure 1).

Work by Burns et al. [2008] revealed the global connections of a once-forgotten feature of the southern ionosphere, the tendency of the late evening ionosphere to increase its density over mid-day levels during summer originally observed by the Halley Bay ionosonde and hence called the Weddell Sea anomaly. With global measurements by COSMIC (figure 2), this feature is seen to be a large region near the Antarctic peninsula, and its formation appears to be connected to the better-known equatorial ionization anomaly. Thermosphere-ionosphere models cannot yet reproduce this feature, even with magnetospheric coupling, so what it is telling us about the extended nature of the ionosphere-plasmasphere interaction remains a curious challenge for ionospheric physics.

COSMIC data also have a key function in mapping the longitudinal variation of the equatorial ionization anomaly, which is thought to be influenced by the eastward propagating zonal wavenumber-3 diurnal tide that is excited by latent heat release in the tropical troposphere [Hagan et al., 2007]. Work by Lin et al. [2007] in collaboration with NCAR scientists examined the structure of this effect using COSMIC data during September equinox. The global three-dimensional ionospheric electron density shows a prominent four-peaked wave-like longitudinal enhancement, and the vertical electron density structures reveal that the feature exists mainly above 250 km altitude (figure 3).


Burns, A. G., Z. Zeng, W. Wang, J. Lei, S. C. Solomon, A. D. Richmond, T. L. Killeen, and Y.-H. Kuo (2008), The behavior of the F2 peak ionosphere over the South Pacific at dusk during quiet summer conditions from COSMIC data, J. Geophys. Res., in press.

Hagan, M. E., A. Maute, R. G. Roble, A. D. Richmond, T. J. Immel, and S. L. England (2007), Connections between deep tropical clouds and the Earth's ionosphere, Geophys. Res. Lett., 34, L20109, doi:10.1029/2007GL030142.

Lin, C. H., W. Wang, M. E. Hagan, C. C. Hsiao, T. J. Immel, M. L. Hsu, J. Y. Liu, L. J. Paxton, T. W. Fang, and C. H. Liu (2007), Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3/COSMIC: Three-dimensional electron density structures, Geophys. Res. Lett., 34, L11112, doi:10.1029/2007GL029265.

Luan, X., and S. C. Solomon (2008), Meridional winds derived from COSMIC radio occultation measurements in winter, J. Geophys. Res., 113, A08302, doi:10.1029/2008JA013089.

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