ESSL LAR 2008: Strategic Goal #1, Priority #3
Earth and Sun Systems Laboratory endeavors are central to NCAR's Strategic Goal #1, Improve understanding of the atmosphere, the Earth system, and the Sun. This Strategic Goal encompasses four Strategic Priorities, each of which is dependent on the efforts and accomplishments of ESSL staff.
ESSL developed an action plan with seven priority themes which involve direct partnerships with the university community and contribute directly to the ESSL Strategic Vision and to several priority items of the NCAR Strategic Plan.
ESSL's seven priority themes:
- Climate projection, with emphasis on short-term prediction.
- Biosphere-Atmosphere-Hydrosphere interactions and specifically development of BEACHON Project (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, Hydrology, Organics and Nitrogen).
- Water system research, specifically the development of the Society, Water, Atmosphere and Natural Systems Project (SWANS).
- An advanced Weather Research and Forecasting system, specifically the development of the Hurricane Intensity and Forecasts (HiFi) Project.
- Space Weather, specifically the development of the Coronal Solar Magnetism Observatory Project (COSMO).
- Chemical Weather, including interpretation of observed data gathered during the Megacity Impact on Regional and Global Environments (MIRAGE) campaign, and the development of a capability for chemical data monitoring and prediction.
- Prediction across scales, specifically the development of an advanced next-generation, climate-weather modeling system and an integrated Earth system model of intermediate complexity.
Goal #1, Priority #3: Improving Prediction of Weather, Climate, and Other Atmospheric Phenomena, is described in the NCAR Strategic Plan as follows: "Understanding of the Earth system is a prerequisite to predicting its behavior, the latter being, however, of a more direct use to many components of society. In that context, for this priority, the key activities within NCAR's laboratories range from improving climate models, to exploring new approaches to prediction across scales, and global and local weather prediction."
This NCAR priority, driven by ESSL's themes 1, 3, 4 & 7, is critical to achieving NCAR's first strategic goal.
The section below describes specific research conducted by ESSL staff under projects relevant to Priority 3. The major ESSL activities in this area involve studies designed to improve prediction of weather, climate, and atmospheric chemistry. The activities center around the use and evaluation of the Weather Research and Forecasting/Advanced Research WRF (WRF/ARW) model, the Community Climate Systems Model (CCSM), and the Nested Regional Climate Model (NRCM).
- Weather Research and Forecasting/Advanced Research WRF (WRF/ARW) - MMM
- Community Climate Systems Model: Advancing Climate Science - CGD
- U.S. Weather Research Program/Short Term Explicity Prediction Program (USWRP/STEP) - MMM
- Data assimilation / ensembles - MMM
- The Observing-System research and predictability Experiment (THORPEX) - TIIMES
- Climate change and regional air quality implications - ACD
- Model physics - MMM
- Chemistry-climate coupling: Past and future - ACD
- Prediction across scales - CGD
- Climate and tropical cyclones - MMM
The overall goal of the WRF model project is to develop a next-generation mesoscale forecast model and data-assimilation system that will advance both the understanding and prediction of mesoscale weather and accelerate the transfer of research advances into operations. WRF has been developed as a collaborative effort among NCAR (ESSL, MMM Division), NOAA's National Centers for Environmental Prediction (NCEP) and Earth System Research Laboratory (ESRL), the Department of Defense's Air Force Weather Agency (AFWA) and Naval Research Laboratory (NRL), the Center for the Analysis and Prediction of Storms (CAPS) at the University of Oklahoma, and the Federal Aviation Administration (FAA), along with the participation of numerous university scientists. WRF is intended to improve the forecast accuracy of significant weather features across scales ranging from cloud to synoptic, with priority emphasis on horizontal grids of 1–10 kilometers. The model incorporates advanced numerics and data-assimilation techniques, a nesting capability supporting multiple and moving grids, and a range of physics options, particularly for treatment of convection and mesoscale precipitation systems. It is well-suited for a wide range of applications, from idealized simulations to operational forecasting, with the flexibility to accommodate a range of potential enhancements.
MMM scientists instigated the WRF endeavor a decade ago to promote closer ties between research- and operational-model development. Since then, WRF has matured to become the most popular mesoscale model in the world. MMM has led the development of the WRF software infrastructure and the Advanced Research WRF (ARW) dynamic core and maintains and supports the system for the research community. The WRF effort provides the primary facility for supporting the NCAR strategic priority of investigation of the dynamics and predictability of weather systems on time scales of 0–48 h. In addition, it furthers NCAR’s mission to provide and support state-of-the-art modeling systems for broad use in the research community.
Within MMM, project activities are distributed across three areas: 1) development and enhancement of WRF capabilities to meet the needs of MMM and community-research objectives; 2) research to advance the understanding and prediction of high-impact weather systems; and 3) model support to the research community. The effort is ongoing as the WRF system evolves to meet future requirements for advanced weather research and forecasting, while timelines attend deliverables in specific funded projects and in commitments to provide modeling capabilities for MMM and the research community.
During the past year, NCAR continued to develop new capabilities for the
ARW and support it to the community. Over 2000 new users registered to download
the code, bringing the total number of registered users to over 7,600. Over
half of this total is non-US users, and 113 countries are represented. In
June 2008 MMM organized and conducted the 9th Annual WRF Users’ Workshop,
with over 225 participants attending from many different countries. MMM personnel
also conducted three user tutorials on the ARW and WRF-VAR. Two ARW tutorials
were in Boulder, with approximately 60 persons, while another was in Seoul,
Korea. Operational forecasting with the ARW continued at NCEP and AFWA (worldwide
regional theatres), as well as a number of international operational applications.
MMM manages the WRF code repository, assists community researchers in development, coordinates additions to the repository, and oversees the code integration and testing for new releases. This past year, MMM released WRF Version 3.0 (April 2008). Key features of V3.0 included:
1. Global ARW;
2. Unified WRF and WRF-Var codes;
4. New and modified microphysics and cumulus schemes;
5. Streamlined infrastructure and memory utilization;
6. New and modified land-surface and PBL schemes;
7. Upper-boundary gravity-wave-absorbing layer; and
8. Simple ocean mixed-layer model.
Improvements were made to the WPS (WRF Preprocessing System) and numerous
bugfixes and enhanced support for a range of computing platforms were included.
As part of the ARW V3.0, a new technique has been developed and implemented to mitigate the artificial reflection of gravity-wave energy from the upper boundary of the model domain, which is well suited for NWP applications. In this method, an implicit Rayleigh damping term is applied only to the vertical velocity in a split-explicit time integration, as a final adjustment at the end of each small (acoustic) time step. The adjustment is equivalent to including an implicit Rayleigh damping term in the vertical momentum equation together with an implicit vertical diffusion of w. This implicit damping for the vertical velocity is unconditionally stable and remains effective even for hydrostatic gravity waves. The good absorption characteristics of this absorbing layer across a wide range of horizontal scales is confirmed though analysis of the linear wave equations, simulations of idealized mountain-waves, and through NWP applications, as reflected by the simulation of mountain waves over the Colorado Rocky Mountains shown in Figure1.
MMM continued to apply the ARW in the Antarctic Mesoscale Prediction System (AMPS) for real-time NWP support for the United States Antarctic Program. Over the past year MMM personnel have incorporated WRF polar modifications developed with collaborator The Ohio State University into WRF V3.0. “Polar WRF” has been tested and found to be superior to regular WRF and to Polar MM5, and MMM has now switched to using the Polar WRF in its AMPS forecasts. The modifications include fractional sea-ice representation and changes to surface characteristics to better capture the conditions of ice sheets. Figure 2 presents an example of a 5-day forecast of surface temperature over Antarctica (20-km grid) using Polar WRF. Polar WRF 3.0.1 is now being implemented into the current version of AMPS. The AMPS group at NCAR has a plan to incorporate the ARW polar mods into the WRF repository, and thus to make Polar WRF available to the community in the next major release (Spring 2009).
MMM has continued to assess and enhance the accuracy of forecasting convective weather systems through real-time convection-resolving forecast experiments with WRF. In support of the NOAA Hazardous Weather Testbed (HWT) 2008 Spring Experiment , MMM ran daily, convection-permitting (3-km grid), real-time forecasts over the central US for the 10 April–6 June period. This year, for the first time, the runs were initialized using WRF-Var, a 3-dimensional variational data assimilation system, with the goal of evaluating the potential benefits of using WRF-Var for initializing the high-resolution ARW runs, as opposed to initializing from gridded operational analyses. To this end, a 9-km ARW run was initialized at 1200 UTC using the GFS, and then cycled every 3 h to produce initial conditions at 0000 UTC (interpolated from 9 km to 3 km). An example of an ARW forecast from this spring experiment is shown in Figure 3. One of the more significant factors in the new approach is that explicit precipitation from the 9-km cycled forecast is now included in the initialization, which was not possible in the “cold start” procedures used in prior years. For many of the cases, this explicit precipitation initialization improved the forecast over the first six hours, as the model did not have to spin up precipitation starting from 0000 UTC. However, the approach also contributed to a number of forecast failures, particularly when the 12-h forecast precipitation features from the 9-km grid did not sufficiently reflect the observed features. This revealed a significant weakness of 3DVAR cycling in the absence of assimilating radar data, which could not be incorporated this year due to time and computer resource constraints. These experiences with WRF-Var will help guide plans for next year’s real-time forecast exercise, in support of the VORTEX2 field program.
Last year’s goals for the ARW effort included assisting domestic and international users of the ARW, conducting the 9th WRF Users Workshop in June 2008 and tutorials in January and July 2008, and a major new release, V3.0. All of these were accomplished. In addition, Global ARW was not only tested, but also released in V3.0, and a new tech note for V3.0 was published. For better management of the WRF code, MMM finalized and published procedures for the administration of the repository and of releases. It also published information for code contributors. Plans for next year include a major release in Spring 2009, the 10th WRF Users’ Workshop, tutorials in Winter and Summer, and continued community support.
The WRF modeling system will continue to serve as a versatile scientific tool for the weather- and climate-research communities. It is a high-performance computational model that scales well from single-processor environments to massively parallel petascale applications. In addition to being a state-of–the-art weather prediction model, it has been adapted to atmospheric chemistry, air quality, and nested regional-climate applications. The successful migration of WRF into operational forecasting yields significant economic and societal benefits. Supporting WRF for widespread community use greatly leverages resources by allowing researchers access to a sophisticated atmospheric tool without a large resource investment, but with the opportunity to contribute to, and benefit from, the advancement of a common modeling system.
The WRF effort within MMM is supported by NCAR/NSF base funds through the MMM budget and USWRP resources, from the NSF Office of Polar Programs, and from outside-funded projects with AFWA, the FAA, and CWB and CAA (Taiwan).
Each year much effort is devoted to further development of the Community Climate Systems Model (CCSM) and those efforts in and of themselves can lead to discoveries about the processes that contribute to climate and its fluctuations. Beyond this, even more is learned about the climate system by applying the CCSM to various outstanding problems concerning the character of the climate and the mechanisms that control its behavior. To this end, members in every section of CGD use the CCSM to investigate a broad range of issues. Below are examples that demonstrate the breadth of topics considered in FY2008.
CAM3, the atmospheric component of CCSM, was been used to attribute the causes of observed atmospheric circulation trends during the second half of the 20th century, in particular the relative roles of direct atmospheric radiative forcing (due to observed changes in greenhouse gases, tropospheric and stratospheric ozone, sulfate and volcanic aerosols, and solar output) and observed sea surface temperature (SST) forcing. CAM3 realistically simulated the observed sea level pressure trends when both types of forcing were considered (upper panels of Fig. 1). Additional experiments showed that direct radiative forcing and observed SST forcing drive distinctive circulation responses that contribute about equally to the global pattern of observed circulation trends (lower panels of figure below). In particular, radiative forcing accounted for much of the observed sea level pressure trends in the high latitude southern hemisphere while SST forcing accounted for the observed sea level pressure trends over the north Pacific and tropics.
CCSM: Polar Regions
The CCSM project continued to take a lead on model developments for polar regions and on studies related to polar climate variability and change. This included the investigation of mechanisms leading to rapid summer Arctic ice loss in CCSM simulations, the potential that these represent "tipping point" or threshold behavior, and the effect that these events have on terrestrial warming and permafrost conditions. Studies using CCSM also assessed Arctic freshwater budget change, with indications that the Arctic hydrological cycle is and will continue to intensify in a warming climate. In related work, CCSM was used to assess the impact that large freshwater discharge has on thermohaline circulation change under present-day and Last Glacial Maximum climate states. Additionally, CCSM simulations were used to study ecosystem impacts in polar regions. Most notably, the CCSM project contributed to studies that resulted in the listing of the polar bear as a threatened species under the Endangered Species Act.
Past investigations of climate change often focused on century timescales, but nearer term changes are of equal interest to society and scientifically distinct in that the initial state of the system may influence its evolution. To estimate the predictability of climate on decadal time scales an ensemble of integrations was performed with CCSM in which the years 2000 to 2062 were simulated. Each realization was forced by the same SRES A1b sequence of climate forcings, but each had a different initial atmospheric state. Due to the chaotic nature of the climate system, the evolution of the state of all model components varied markedly from one realization to another, but there were indications of predictable phenomena in the experiment. For example, the ensemble mean of the Pacific Decadal Oscillation had a predictable signal for more than 40 years.
2009 and Beyond
Applications of CCSM will continue on a wide range of topics. Examples related to the investigations outlined above include:
Attribution of atmosphric circulation: The work on attribution of atmospheric circulation trends with CAM will be continued in FY09 to include future climate states simulated by the CCSM model under the SRES A1B scenario. In addition to prescribing the full SST and atmospheric radiative forcings in CAM for the next 50-100 years, the forcings will also be decomposed into their natural and anthropogenic components for enhanced attribution.
Continuted terrestrial carbon cycle model development: There will be continued development of the terrestrial carbon cycle model, including additional capabilities to simulate dynamic vegetation, anthropogenic land cover change, croplands, wildfire, and biogeochemical cycles. As the model matures, a primary scientific theme will be to examine natural and human-mediated changes in land cover and ecosystem functions and their effects on climate, water resources, and biogeochemistry.
Polar region model development: Numerous model improvements targeted at polar regions will be included in the next generation CCSM model. These include improved sea ice albedo parameterizations, permafrost dynamics, dynamic vegetation processes, and cloud microphysics, among others. This will allow for more reliable polar climate simulations. Additionally, it will enable new research on the role of these processes in climate variability and change. For example, the incorporation of black carbon cycling within the sea ice and terrestrial snow components will permit us to assess the role that increased soot deposition has played in the warming Arctic climate. In the longer-term, the incorporation of an ice sheet model within the CCSM system, which is currently underway through a collaborative effort with the Los Alamos National Laboratory, will allow improved simulations of sea level rise and the influence of ice sheet change on climate.
Predictability signatures: The ensemble of SRES A1b scenario integrations will be further expanded so that signatures of predictability can be detected with greater levels of significance. And the dynamical mechanisms and atmosphere-ocean interactions that contribute to the decadal predictability will be diagnosed and compared to existing theories of intrinsic modes of North Pacific variability. Moreover, studies of decadal predictability in other basins will be furthered.
The Short Term Explicit Prediction (STEP) Program (http://www.mmm.ucar.edu/STEP) is a multi-NCAR-Laboratory activity to improve the short-term forecasting of high-impact weather such as severe thunderstorms, winter storms, and hurricanes. Improving short-term forecasts of such weather can have significant societal and economic benefits, including: (1) reduced fatalities and injuries due to weather hazards; (2) reduced private, public, and industrial property damage; and (3) improved efficiency and savings for industry, transportation, and agriculture. The STEP Program is also being stimulated by the significant advancement in a number of fields that are required to make progress in this area. These include the ability to observe the four-dimensional structure of the atmosphere, the development of new data-assimilation techniques, such as 3DVar/4DVar and the Ensemble Kalman Filter (EnKF), and the continuing development of numerical-modeling systems, such as the Advanced Research/Weather Research and Forecasting model (WRF/ARW), which can be run at grid resolutions that properly represent the physical processes critical to the production of such hazardous weather. The program includes research into basic understanding of high-impact weather systems, development of forecast techniques, real-time testing of forecast systems, verification, and interaction with users. This collaborative effort incorporates national and international scientists, engineers, and operational personnel from universities, government institutions and the private sector.
The primary activity for STEP this year was the collaborative effort on an IHOP retrospective study. STEP scientists specializing in various topics, ranging from mesoscale observation analysis, automated nowcasting, high-resolution data assimilation, high-resolution WRF-ARW modeling, and convective precipitation verification, participated in the study. A workshop was conducted in July 2008 to report on progress for each project and to discuss future coordination and publication of the results. In order to better accomplish the STEP goal as stated in the STEP strategic plan, a process to redistribute the STEP funds for FY08 and 09 funding cycle was conducted. On the research level, a wide range of activities which are central to STEP research goals, and which involve MMM, RAL and EOL scientists have been ongoing over the past year(s). Within MMM, WRF/ARW development efforts continued to be a critical component of STEP, offering a range of new capabilities, from improved numerics and physics to new data-assimilation systems that can address the short-term forecast problem. The data-assimilation systems based on 3DVar, 4DVar, and EnKF techniques continued to be developed, and research on the inclusion of radar observations into these systems was emphasized for the STEP program.
Other than the variety of basic research and development, one of the major themes in STEP is to demonstrate high-resolution forecasting systems in real time. In collaboration with the Spring 2008 SPC/NSSL Hazardous Weather Testbed experiment, WRF/ARW was run at a 3-km horizontal grid resolution over the central U.S. to produce explicit 0-36 hour convective-weather forecasts. The WRF/ARW run was initialized by the 3DVAR data-assimilation system with a 9-km resolution. These forecasts were evaluated by forecasters and researchers from across the country, and exhibited noticeable improvements over past years, especially as regards the representation of convective precipitation. STEP's nowcasting system and the radar data assimilation system VDRAS were demonstrated in Beijing during the Olympics 2008 as part of the WMO sponsored Olympics forecasting demonstration project. VDRAS produced 3-km wind, temperature, and humidity analyses updated every 12 minutes. A number of STEP scientists participated in the planning and the actual execution of the Terrain-induced Monsoon Rainfall Experiment (TiMREX) which was conducted in southwest Taiwan.
In the coming year, the IHOP retrospective studies will be completed and a number of publications will be written to summarize the results. A workshop will be held in December to present findings from these studies. Comparisons will be made to evaluate strengths and weaknesses of each data assimilation, nowcasting, and forecasting systems and the impact of including radar in the assimilation. Efforts at developing new techniques for verifying high-resolution forecast guidance will be continued. Future development of verification will focus on this inter-comparison to understand the strengths and weaknesses of different approaches. Efforts on studies of convective weather dynamics based on observations and model results will also be continued.
Data assimilation is the process of combining observations and a previous forecast to provide a gridded estimate of the atmospheric state at a certain time. These estimates can then be used as initial conditions for subsequent forecasts or as tools to analyze and understand the atmosphere. While much progress has been made at global scales, data assimilation for scales of less than a few hundred kilometers (the "mesoscale," where most severe and damaging weather occurs) remains a significant open problem in atmospheric science. Mesoscale data assimilation is especially challenging for two reasons. First, mesoscale motions are intimately coupled to complex physical processes such as those involving moisture, cloud and rain or interaction with the land or ocean surface. These processes are difficult to represent accurately in numerical models. They also lead to distinct and strongly nonlinear dynamics at the mesoscale, so that balances between mass and wind, which pertain at large scales in the atmosphere and underlie global data assimilation schemes, are questionable at the mesoscale. Second, observations that are plentiful (e.g., Doppler radar measurements of wind and reflectivity) involve only a subset of atmospheric variables, while observing platforms that measure all relevant variables (i.e., radiosondes) are sparse and resolve mesoscale motions poorly. To overcome these difficulties, there has been substantial effort within ESSL/MMM to advance mesoscale data assimilation.
A significant component of these efforts has been to build, and support for the community, a data assimilation facility for WRF based on variational assimilation techniques, known as WRF-Var. The WRF-Var system continues to be widely used in research at universities and as the basis for operational assimilation system development at the U.S. Air Force Weather Agency (AFWA) and several other operational centers internationally. WRF-Var has been extended from three to four dimensions (WRF 4D-Var) to meet the increasing demand for improving initial model states in multi-scale and time-dependent numerical simulations and forecasts. WRF 4D-Var uses the WRF model adjoint as a constraint to impose a dynamic balance on the assimilation. It has been demonstrated to evolve the background error covariance and produce the flow-dependent analysis increments. Recent experiments with Doppler-radar observations have shown the potential of WRF 4D-Var for high-resolution assimilation with explicit representation of moist convection (Fig. 1). These results illustrate clear advantages of 4D-Var over the existing 3D-Var for this problem.
ESSL/MMM also has a strong research program in the area of ensemble-based data assimilation. In collaboration with the Data Assimilation Research Section within CISL/IMAGe, an ensemble Kalman filter for WRF has been developed within the Data Assimilation Research Testbed; this assimilation system is known as WRF/DART. Assimilation of Doppler-radar observations is also an emphasis of WRF/DART research and multiple case studies using WSR-88D observations of severe convective storms have been completed. These case studies indicate an overall analysis quality comparable to or better than traditional dual-Doppler retrievals, besides providing gridded analysis of WRF’s microphysical and thermodynamic variables. Several areas important for continued improvement of radar assimilation have also been identified. Most crucial are better representations of forecast-model errors in the assimilation process and the extension to larger domains to include multiple spatial scales, spanning both meso- and convective-scale motions.
THORPEX seeks to reduce and mitigate the effects of natural disasters on society by transforming timely and accurate weather forecasts into specific and definite information in support of decisions that produce the desired benefits.
One aspect of the TIIMES mission is to be the administrative home of programs that cut across the divisional and laboratory structure of NCAR. One such effort is THORPEX (The Observing-System Research and Predictability Experiment), which is a long-term effort within the World Meteorological Organization’s World Weather Research Program (WMO/WWRP). The overarching goals of THORPEX are to accelerate both the forecast skill of high impact weather events on the 1 to 14-day time scale and utilization of forecast information. THORPEX research is meant to benefit society, the economy and the environment with one focus to mitigation of disasters in the developing world. While THORPEX was designed to concentrate on the 1 to 14-day time-scale, THORPEX is also developing collaborations with the World Climate Research Program for time-scales that fall between the time-scales of numerical weather prediction and climate projections. These time-scales include seasonal prediction and longer subseasonal time-scales, such as the Madden Julian Oscillations. The THORPEX and the WCRP collaboration includes research on topics of mutual interest (e.g., improving the characterization in numerical models of a variety of processes that include tropical convection, polar precipitation events and the triggering and enhancements of Rossby wave trains).
TIIMES has hosted both the US THORPEX Project and the co-chair of the North American THORPEX Regional Committee until 28 February 2008. David Parsons held both these posts. He is now on a Collaborative Visit to the WMO to become the Chief of the WWRP and Manager of the THORPEX International Project Office. The THORPEX research effort in the US already has significant participation within the university community and the effort has the potential to involve weather and climate researchers within ESSL at NCAR and the activities of CISL, RAL and SERE. One aspect of THORPEX is to move the user and research community from relying on deterministic forecasts to ensemble forecast systems that better represent the uncertainty in simulations of the non-linear, partly chaotic nature of the atmosphere. During the past year, NCAR CISL initiated an archive of the ensemble members of the ensemble global forecasts of the major operational forecast centers, which when fully operational will include ~256 ensemble members produced daily for forecast periods from 1 to 14-days. The archive includes the basic model derived parameters as well as derived parameters that are of interest to researchers. This ensemble archive is called TIGGE (THORPEX Interactive Grand Global Ensemble). TIGGE is well utilized by the research community as, for example, over hundred users have registered.
Parsons was also the Principal Investigator for two major international field experiments with accompanying numerical modeling efforts called THORPEX Pacific Asian Regional Campaign (T-PARC) and CONCORDIASI until he took on the position of international oversight of THORPEX and the WWRP. The goals of T-PARC are to advance understanding and improve prediction of i) high impact weather over the western Pacific and east Asia with a focus tropical cyclones from genesis to extratropical transition (ET) or decay; ii) downstream high impact weather events over North America, the Arctic and Europe whose dynamical roots and forecast errors are over the western Pacific and east Asia. The tropical cyclone and ET phases of T-PARC took place from August to early October 2008. A winter phase planned for January to March 2009. T-PARC, and a collaborative Office of Naval Research project called TCS-08 (Tropical Cyclone Structure) experiment is one of the largest coordinated efforts of the international research and operational community to address tropical cyclones in the Pacific and their impacts on downstream flow.
The CONCORDIASI project has begun and will end in early October 2009. This program has multi-disciplinary goals, such as i) more accurate representation of the atmosphere over Antarctica through advancing satellite data assimilation for weather prediction and the climate record, ii) advancing prediction of precipitation events near Antarctica and the impact of these events on lower latitude circulations; iii) more accurate prediction of ozone concentrations through Lagrangian measurements of ozone depletion and the microphysics of stratospheric NAT clouds.
A new THORPEX effort that involves significant collaboration with the World Climate Research Program (WCRP) is called the Year of Tropical Convection (YOTC - see below).
Mitch Moncrieff (MMM) and Duane Waliser (JPL-CalTech) are leading a major new international project described as follows. Incomplete knowledge and practical issues severely disadvantage the skill of numerical weather prediction models and climate models, for example, the reliable representation of prominent tropical phenomena such as the InterTropical Convergence Zone (ITCZ), El Nino/Southern Oscillation (ENSO), monsoons and their active/break periods, the Madden-Julian Oscillation (MJO), tropical-subtropical transition, and easterly waves/ tropical cyclones Furthermore, tropical convection has long-range effects on stratospheric-tropospheric exchange, the large-scale circulation of the upper-atmosphere, and the variability of weather and climate around the world. Convective organization is involved at a basic level.
In order to address this major challenge, WCRP and WWRP-THORPEX proposed a year of coordinated observing, modeling, and forecasting, which led to the Year of Tropical Convection, YOTC. The focal theme of YOTC is the role of organized tropical convection at large scales. Together with accompanying research activities, the YOTC seeks to advance knowledge, diagnosis, modeling, parameterization, and prediction of multi-scale tropical convection and two-way interaction between the tropics and extra-tropics. The YOTC project will exploit the vast amounts of existing and emerging observations, the expanding computational resources, the new, high-resolution modeling frameworks, and theoretical insights (see Figure 3). This activity involves unprecedented collaboration between international programmatic activities, the operational prediction, research laboratory, and academic communities. Global databases of satellite data, in-situ data, and high-resolution model analysis and forecasts will be constructed. Emphasis is on timescales ranging from days-to-months; that is, the intersection of weather and climate.
The following objectives were achieved this year:
i. the ECMWF T799 (25 km) global analysis, forecast products, and special diagnostics being archived at ECMWF will be available to the community;
ii. the YOTC Science Plan was drafted;
iii. the YOTC Implementation Plan is in the first stage of development.
Started in May 2008, YOTC will contribute to the Asian Monsoon Year (AMY), the THORPEX Pacific Area Regional Campaign (TPARC), the United Nations Year of Planet Earth, and the International Polar Year. The scientific basis for YOTC is published in Moncrieff et al (2007), and a brief summary is published in Waliser and Moncrieff (2007).
Globally, secondary organic aerosol (SOA) from biogenic precursors surpasses those from anthropogenic sources. These organic particles impact climate directly by scattering and absorbing of radiation, and indirectly through the modification of clouds and precipitation. These processes exert a substantial influence back upon the earth system through links to the terrestrial carbon and water cycles (e.g., precipitation regulates plant growth and thus emissions of organic compounds). Understanding the feedbacks between the atmosphere and terrestrial environment is key to estimating the impact of climate change on regional air quality.
In the past year, ACD scientists collaborated with Jack Chen, Jeremey Avise, and Brian Lamb (Wash. State U.), Cliff Mass (U. Washington), Donald McKenzie and Susan Fergusen (US Forest Service) to investigate the impact of future climate and land cover on regional air quality in the Pacific Northwest and North Central U.S. The results indicate that U.S. regional air quality (e.g., ozone and particles) will degrade even if U.S. anthropogenic emissions remain the same. The changes are due to a combination of pollutant transport from other countries (primarily China, Mexico and Canada), changes in wildfire emissions, and changes in biogenic emissions. The increased pollution transport is due to predicted increases in emissions in these countries. Wildfire activity is predicted to increase due to a warming and drying climate. Biogenic VOC emissions are expected to increase in response to higher temperatures. Land use change (i.e. tree plantations, agriculture, and urbanization) scenarios result in dramatic increases in some regions and decreases in other areas.
ACD scientists, collaborating with researchers from the University of Colorado, have also created a new emissions inventory of sesquiterpenes from vegetation using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). These emissions were input to a regional chemical transport model so that the impact of these compounds on secondary organic aerosol (SOA) concentrations could be evaluated. The results, plotted in Figure 1, show that sesquiterpenes from vegetation roughly doubled the amount of SOA simulated when compared to simulations without sesquiterpenes; however, the model still underpredicted particulate organic matter when compared to observations.
Other modeling efforts in ACD have focused on investigating the role of dust aerosol in the heterogeneous removal of reactive nitrogen species in the vicinity of Mexico City. Changes in pollutant concentrations (i.e. nitric acid, nitrates) including the impact on ozone at the regional scale were quantified using WRF-chem model and observations from the MILAGRO field campaign. During the next year, modeling efforts relating to the roles of aerosol in coupling atmospheric chemistry with climate include work on characterizing carbonaceous aerosols observed in the Mexico City area in terms of their chemical composition, origin (i.e. anthropogenic, biogenic, biomass burning) and spatio-temporal variability. The predictions of these models will then be compared with measurements using the Aerosol Mass Spectrometer (AMS) at several sites from MILAGRO.
In order to improve on uncertainties relating to the indirect effects of aerosols on climate, ACD scientists have added a new aerosol scheme using a modal approach to the global models. Current evaluations of this scheme focus on evaluating warm cloud indirect effects, and on adding ice cloud formation to the models.
The Weather Research and Forecasting (WRF) Model is being used in an increasingly wider set of applications as computing power improves. WRF was developed as a community mesoscale model for numerical weather prediction, case studies, and idealized simulations, and as a tool for related applications such as air-quality research and forecasting. Some examples of newer applications that have resulted from improved computing resources are real-time cloud-resolving forecasting, including moving-nest hurricane forecasting, and nested regional-climate modeling. With these applications come new priorities in physics development to enable better hurricane and regional-climate modeling. These priorities fit with several of ESSL's priorities, including those of weather prediction and simulation across scales. Furthermore the aim of providing the university research community with a relevant up-to-date modeling system is met by continually updating the model to make use of the new capabilities in the current computing era, and improvements in model physics form one critical aspect of this development.
WRF already has a large set of physics options designed for its range of uses, from fast-physics packages for operational uses, to more complex packages for scientific studies. The table shown summarizes the current WRF physics options available to the ARW dynamical core as of its last release (Version 3.0) in April 2008. Version 3.0 also included a new global model capability, and extended the large-eddy simulation (LES) PBL capability to interact with land-surface fluxes.
Ongoing physics collaborations exist with NCEP, NASA Goddard, the EPA, NRL, NOAA/ESRL, the Pacific Northwest National Laboratory, Colorado State University, UCLA, the University of South Florida, University of New Mexico, and YonSei University (Seoul, Korea), as well as across the NCAR Divisions and Laboratories. Many of these reached fruition with more options for the WRF user community in the Version 3.0 release. Support for this work included NSF, KMA, AFWA, ARO, and the FAA.
Plans for FY09 include further collaboration with the CCSM modeling group to include some CCSM physics options and capabilities for regional-climate simulations. Also gravity-wave drag and spectral-nudging capabilities are being developed in addition to more physics options including sub-grid turbulence, radiation and microphysics development in a variety of collaborative projects.
1. Lower stratospheric trends
In continuation of the work performed under FY2008, we have expanded our analysis of the lower stratospheric as simulated by CAM-chem (paper published in Journal of Geophysical Research, 2008). In this subsequent analysis, we focus on the understanding of the trend in the lower stratospheric tropical (20°S-20°N); using different simulations with different subsets of forcing agents we show that, based on this model, climate change (as identified here by changes in CO2 and sea-surface temperatures) is the largest contributor to the ozone trend in that region, much larger than the contribution of ozone-depleting substances; this work is submitted to Geophysical Research Letters. Additional studies will be performed during FY2009; in particular, focus will be given on changes in the width of the tropics and changes in tropospheric composition. This work was funded by DOE.
2. Impact of sectoral emission change
In support of the US Climate Change Science Program (DOE), we have performed and analyzed in collaboration with NASA-GISS and NOAA-GFDL a series of simulations where emissions from specific sectors (transportation for example) are reduced by 30% over a specific region. This is to identify the potential chemistry and climate impact regional pollution control measures; in particular, over the United States, transportation is the sector which has the largest impact. This work in submitted to Atmospheric Chemistry and Physics Discussions. This work was funded by DOE.
3. Methane clathrates
In continuation of the work performed under FY2008, we have furthered our investigation of the potential role for methane clathrates to act as a strong methane source during the 21st century. Using a combination of model simulations from IPCC AR4 and model results for under the seafloor methane destabilization, we show that it is unlikely that methane from clathrate destabilization will be a strong source of methane by the time CO2 as doubled over pre-industrial conditions (i.e. second half of 21st century). This work is in press in Geophysical Research Letters. This work was funded by DOE.
The Prediction Across Scales initiative is a collaborative effort between CGD and MMM to coordinate research and system development activities across weather and climate scales. Recent major advances in petascale computing coupled with rapid advances in scientific understanding are enabling progress in simulating a wide range of physical and dynamical phenomena with associated physical, biological and chemical feedbacks that collectively cross the traditional weather-climate divide. Such simulations and predictions are essential to a society that is becoming much more sophisticated in its requirements for weather, air quality and climate predictions and that is able to make useful economic and social use of such improvements. Moreover, fundamental barriers to advancing such prediction on time scales from days to years, as well as long-standing systematic errors in weather and climate models, are partly attributable to our limited understanding and capability to simulate the complex, multiscale interactions intrinsic to atmospheric and oceanic fluid motions. The scientific and societal questions and issues to be addressed are many. A limited sample includes better understanding of
- The water cycle and its predictability, particularly the limitations of available water and the impacts on food production;
- The limits of weather, air quality and climate predictability including the impacts of mega-cities and the stressed Earth's capacity to sustain quality of life;
- The interaction of hydrological, chemical and biogeochemical cycles and their feedback on weather/climate processes;
- The mechanisms by which solar variations influence the chemistry and dynamics of the upper atmosphere, and how these effects are manifested in the lower atmosphere;
- The interactions between climate change, ENSO and other natural modes of variability, including changes to the behavior of phenomena like hurricanes; and
- The mechanisms of abrupt climate change and potential tipping points.
The enabling tool for much of this research will be a community Nested Regional Climate Model (NRCM). The result of this ambitious effort to combine high resolution regional atmosphere and ocean models with a state-of-the-science climate model will be fundamental progress on the understanding and prediction of regional climate variability and change. In particular, embedding Advanced Research WRF (ARW) and a Regional Ocean Model System (ROMS) within CCSM will allow scientists to resolve processes that occur at the regional scale, as well as the influence of those processes on the large-scale climate, thereby improving the fidelity of climate change simulations and their utility for local and regional planning.
As a first step toward the development of NRCM, NCAR and community scientists completed a 1995-2005 simulation of the tropical circulation with the NRCM configured in a channel mode at 36 km resolution using NCEP/NCAR reanalysis data on the poleward boundaries and specified surface conditions. A set of comparative simulations were also made using the atmospheric component of CCSM at T170 resolution configured in a similar channel mode with relaxation towards reanalysis in the polar regions. In addition, several high resolution two-way interactive simulations inside the channel model were completed, including high resolution nested domains over the Maritime Continent and the North Atlantic. These simulations utilized NCAR, NASA and DOE computing resources, and they are currently being analyzed by a number of NCAR and external scientists. The results will be featured in a special issue of Climate Dynamics in 2009.
In addition, progress was made over the past year nesting of ROMS within CCSM in two-way interactive mode. Initial experiments were conducted in the eastern Pacific Ocean with the goal of improving the poor performance of climate models in this region. This work will also provide a platform to include higher trophic level marine ecosystem models into CCSM.
2009 and Beyond
A new set of simulations began in FY2008 and will continue into FY2009 through the support of CISL. These experiments are designed to study the potential impacts of climate change on North Atlantic hurricane activity and on water resources over the intermountain West. They consist of a series of one-way nested simulations with interior ARW domains at ~4 km resolution over the intermountain West and the Gulf of Mexico. A coarser resolution (36 km) domain encompasses both regions, as does a higher resolution 12 km domain (Figure 1). The large-scale forcing data is provided from A1B and A2 scenario CCSM-3 T85 integrations using a time-slice approach, which will allow an examination of the fidelity of the simulation against current climate as well as project likely future changes in regional weather statistics. The results will be used to advise two communities on potential climate changes:
- vulnerable coastal communities and the offshore oil industry on potential changes in hurricane intensity and frequency in the Gulf of Mexico over approximately the next 50 years; and,
- a diverse group of stakeholders (government planners, water managers, terrestrial ecologists, etc.) on the changes in water resources in the western Intermountain states.
More generally, the experiments will:
- allow a further assessment of the skill of ARW for climate applications at high resolution over both tropical and extratropical domains, which is important for future model development as well as the ultimate NRCM goal of two-way nesting ARW within CCSM;
- draw into NRCM a much larger base of "earth system scientists", all of whom require climate data on scales of a few kilometers (or less); and,
- produce unique data sets of a climate change scenario that would be of immense interest to many stakeholders.
The impact of climate change on hurricanes has continued to be investigated and expanded to include the upscale influence of hurricanes on climate. An earlier study that showed a marked increase of 50% in the global proportion of the most intense hurricanes, which caused considerable controversy, has been validated by a new study using a completely independent data set. A further study has shown that the North Atlantic is now experiencing 2-3 times the proportion of category 5 hurricanes compared to previous activity. A major new modeling study with the NRCM to investigate future hurricane changes and variability has commenced with support from the Willis Research Network and the Research Partnership to Secure Energy for America. This includes NRCM projections at resolutions of 12 and 4 km, sufficient for the first time to resolve the intensity and structure of major hurricanes. A new study has provided a strong indication that hurricanes may have a substantial upscale role on climate through their vertical and horizontal transports of energy.