Goal 1, Priority 3: Improving Prediction of Weather, Climate, and Other Atmospheric Phenomena
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.
FY2007 Accomplishments
Click to enlarge. Data is being analyzed from the T-AMMA project to investigate and improve the performance of the driftsonde, shown above, as a research tool. (Photo by Terry Hock)
To a large degree, improving prediction of atmospheric and related phenomena requires improved understanding of the underlying process drivers. Among the FY2007 highlights that address these capabilities are analyses of data gathered during the FY2006 THORPEX-African Monsoon Multidisciplinary Analyses (T-AMMA) field campaign, which investigated and improved the performance of driftsondes as a research tool, and investigated hurricane genesis and the genesis environment.
RAL continued to work with scientists from EOL in analyzing data from the 2005/06 Refractivity Experiment For H2O Research And Collaborative operational Technology Transfer (REFRACTT). Considerable effort has been spent on data quality control and re-calibration of the refractivity fields in preparation for case study analysis of convection initiation and assimilation of the refractivity data into a numerical model. Approximately six cases from REFRFACTT-2006 have been identified for detailed analysis on the variability of water vapor in the near-surface boundary layer in the pre-storm environment and its role in the initiation of new convection. One of the cases is highlighted in a paper on REFRACTT-2006 that we are preparing for submission to the Bulletin of the American Meteorological Society.
RAL, ESSL/MMM, and EOL conducted significant research within the NSF-sponsored Short-Term Explicit Prediction (STEP) program. This work, aimed at improving zero-to-six hour forecasts of high-impact weather provides funding to a number of scientists working to improve forecasting of convective weather, gain better understanding of the interaction of the land surface and the atmosphere, improve microphysical parameterizations, and develop better tools for evaluating weather forecasts.
A new bulk microphysical scheme for WRF has been developed at RAL, incorporating a new snow particle size distribution scheme based on aircraft observations that represents snow particles as a sum of exponential and gamma distributions. RAL scientists also conducted a detailed microphysical study of two winter storms occurring during the IMPROVE (Improvement of Microphysical PaRameterization through Observational Verification Experiment) II field program. An unexpected finding was that freezing drizzle formed outside convective updrafts and ice crystals formed in convective cores. These observations suggest that ice nuclei depletion and ice formation via supersaturation need to be included in microphysical parameterizations in order to properly simulate these types of storms.
Click to enlarge. Very high-resolution (150 meter) simulations of hurricanes under idealized conditions were run on NCAR's “blueice” computer. Initial results indicate increasing simulated intensity with higher resolution. A second important finding is that for fixed external conditions (under ambient environment sea-surface temperature, for example), the simulated internal variability of storm intensity is relatively small. The latter result gives rise to the hope that hurricane-intensity changes may result as a response to changes in external conditions, which are more easily predictable.
View AnimationNCAR’s dynamics and predictability work in FY2007 also focused on hurricanes with a special grant of computer time on NCAR's blueice, enabling testing of very high-resolution simulations of hurricanes under idealized conditions. Initial results indicate increasing simulated intensity with higher resolution. A second important finding is that for fixed external conditions (under ambient environment sea-surface temperature, for example), the simulated internal variability of storm intensity is relatively small (Figure left below, blue curve), even though the three-dimensionality of the flow is apparent (Figure right, below). The latter result gives rise to the hope that hurricane-intensity changes may result as a response to changes in external conditions, which are more easily predictable.
RAL scientist, Thomas Hopson, worked with Peter Webster and colleagues at the Georgia Institute of Technology, as well as with members of the Asian Disaster Preparedness Center, in developing Climate Forecasting Applications for Bangladesh. Using European Centre for Medium Range Weather Forecasts (ECMWF) forecast products and NASA and NOAA precipitation estimates, the group produced short-range (1- to 10-day) and long-range (1- to 6-month) forecasts of upper catchment discharges from the Brahmaputra and Ganges Rivers. Medium-range forecasts (20- to 25-day) were produced using a statistical model to bridge the short and long-range time scales. The operational flood forecasts they issued in July and August 2007, and disseminated through a network of local and regional organizations, has been credited with saving tens of thousands of lives.
Click to enlarge. Figure a shows the average January precipitation amount based on MM5 simulations, for the inner computational domain at 15 km horizontal grid spacing. The rain gauge data in Fig. b are consistent with the MM5 estimates, and the coastal amounts of precipitation from the satellite/gauge merged data set show a similar pattern (Fig. c). Visual comparison of the amount and geographic distribution of monthly rainfall between model and the observations reveals considerable skill in the model simulation.
A new Climatological Four Dimensional Data Assimilation (C-FDDA) System has been developed at RAL to facilitate climate downscaling using the MM5 or WRF models. In 2007, CFDDA was used to generate a climatography for a region of interest to the U.S. Department of Defense (DoD); typical boundary layer conditions were used to define likely directions and speeds of hazardous-material transport for different seasons and times of day. C-FDDA is also being used to create a global mosaic of moderate resolution (~40 km) climatographies for the 1979-2005 period. This database will be used by state, and local emergency managers for predicting the effects of accidental or intentional releases of hazardous material. And finally, C-FDDA is being used to study the hydro-climatology of the eastern Mediterranean and the adjacent countries of the Middle East, where the balance between water supply and demand could be significantly altered by climate change.
Investigations on the impact of future climate and land cover on regional air quality in the Pacific Northwest and north central U.S., performed by ESSL/ACD scientists, as well as several university partners, and the U.S. Forest Service also falls under this priority. Results indicate that U.S. regional air quality (e.g., ozone and particles) will degrade even if U.S. anthropogenic emissions remain the same. See the ESSL LAR for more details on this research.
The Pentagon, and its 25,000+ occupants, represents a potential target for a terrorist attack using chemical, biological, or radiological material released into the atmosphere. In response to this concern, DoD has engaged RAL to develop a building-protection system called Pentagon Shield (PS). The PS system assimilates meteorological and contaminant observations from remote and in-situ sensors into a complex linked system of models that operate together to represent processes–from mesoscale to building scale. In the event of a hazardous-material release, the system calculates the properties of the contaminant source (e.g., location), the current characteristics of the contaminant plume, and the future path of the plume. In 2007, the modeling domain of the system was expanded to cover all of Arlington County, Virginia. This new “Urban Shield” domain will support emergency response efforts in the area.
FY2008 Plans for Strategic Priority 3
NCAR’s labs have a variety of plans for improving prediction capabilities in FY2008, including:
- Scientists involved in the Short Term Explicit Prediction (STEP) program will conduct an International H2O Project (IHOP) retrospective study to evaluate and further develop NCAR's data assimilation, nowcasting, and short-term forecasting systems for high impact weather prediction. Some of these systems will be used and evaluated in a real-time forecasting demonstration during the 2008 Beijing Summer Olympics.
- ESSL/ACD scientists will continue field and laboratory studies of the impact of climate change on regional air quality.
Lastly, improving short-term climate simulations at regional scales requires finer (in both the horizontal and vertical) resolution models, and perhaps ultra-high resolution modeling through two-way regional nesting. Opportunities in this area in FY2008 and beyond include:
- Simulations with and without data assimilation between about 1980 and 2005, which can be used to address predictability of the climate system on decadal timescales.
- Examining the implications for hydrology and water supplies that are controlled by local mountainous topography (e.g., snowpack and runoff in the West)
- Developing better understanding of the likelihood of changes in extremes, such as extended heat waves, floods, droughts, and Atlantic hurricane frequency and intensity.
Initial results from RAL’s C-FDDA are a first step toward downscaling global model simulations of future climates for that region. The preliminary simulation will be repeated later without the use of observations but using “grid nudging” toward the driving analysis to keep the model analysis from drifting. This process of model verification and adaptation for the area will then be repeated with WRF for the entire winter season, when most precipitation occurs. The model that better represents the regional and local climate will be selected and run for the same period using lateral-boundary conditions from a simulation of the present global climate by the NCAR Community Atmospheric Model, driven by observed sea-surface temperatures and land use. Lastly, the regional model will be run with lateral-boundary conditions provided by future climate simulations conducted for the Fourth IPCC assessment report with the coupled ocean-land-atmosphere CCSM. This regional-model output will be compared with regional-model simulations of present climate in order to assess the impact of future climate forcing scenarios on the components of the water cycle in this geographic area.
The Urban Shield system will be enhanced during FY2008 by upgrading the transport and dispersion model to account for dense-gas effects and adding a variety of release source models–including Terminal Doppler Weather Radar data in the Variational Doppler Radar Assimilation Systems within Shield, and porting the transport model to run on high-speed Graphics Processing Unit hardware.
Related Lab Annual Report Sections:
Goal 1, Priority 3