1.

Ensemble Forecasting on the Mesoscale: Storm-scale prediction with the ensemble Kalman filter (EnKF)

2.

Experimental numerical weather prediction: AMPS model serves Antarctic forecast needs

Powers, Manning, and Kuo, in collaboration with Bromwich (OSU), developed the Antarctic Mesoscale Prediction System (AMPS). AMPS is an experimental system generating twice-daily MM5 forecasts, at resolutions as high as 3.3-km, in support of the U.S. Antarctic Program. This past year, AMPS contributed to the success of yet another international emergency operation in Antarctica. In June 2002, the German supply ship Magdalena Oldendorff became trapped in thickening sea ice. South Africa dispatched its vessel Agulhas to retrieve the trapped personnel by helicopter. The South African Weather Service relied heavily on the AMPS forecasts during the event. AMPS accurately forecast both the poor weather hampering the Agulhas' voyage, as well as favorable conditions allowing the final helicopter airlifts. The figure presents an example of an AMPS forecast during the transit of the Agulhas (position marked by "X") to the Oldendorff (position marked by dot).

3.

Cloud microphysics and precipitation: Microphysical properties of storms during STEPS

4.

Advanced data assimilation systems for community use: Real-data applications of WRF 3DVAR

5.

WRF model numerics: High-order numerical methods in WRF

In an effort to improve the accuracy of numerical simulations over complex terrain, Klemp and Skamarock, in collaboration with Fuhrer (SFIT, Zurich), documented the presence of artificial disturbances that can arise in flow over small-scale terrain. They demonstrated that these errors are contained in the linear system of equations, and they explained their behavior through analytic solutions to the steady-state, finite-difference equations. This work has led to improvement of the numerics in the WRF Eulerian prototypes. The Eulerian, terrain-following mass coordinate, split-explicit, flux-form prototype has been chosen as the official WRF core to be supported for community use. The Eulerian mass and height coordinate WRF cores use the 3rd order timesplit Runge-Kutta scheme, which has proven to be both robust and efficient. For example, using daily operational forecasts produced at NCAR and FSL, Baldwin (NSSL) and Matt Wandishin (UA) produced power spectra for precipitation, and compared it with observationally-derived spectra and spectra derived from the operational Eta model. They found that the WRF model reproduced the observed spectra much better than even the much higher resolution operational Eta model (see figure) lending further evidence that high order numerical methods should be employed in high resolution NWP models.

6.

Software development: Advanced Software Framework

WRF's software is designed to be flexible, maintainable, extensible, efficient, and portable to a range of high-performance computing platforms. The software infrastructure is called the WRF Advanced Software Framework (ASF). This is the foundation for the WRF model itself and for the WRF 3DVAR system. With support through the NCAR Initiative program, development this past year has focused on computational and I/O performance enhancement, new dynamical core development, nesting, and model coupling.

7.

WRF testing and verification: WRF real-time CONUS forecasts

WRF real-time forecasts were used to evaluate the model under a variety of weather conditions, and to test the model's robustness. NSSL conducted precipitation verification for CONUS forecasts, and FSL (Loughe) verified precipitation forecasts from the central-U.S. 10-km domain during the field experiment IHOP. An exciting endeavor this past year was the running of a CONUS domain at 10-km resolution. This was facilitated by FSL, where the model is run on its computer "jet" twice daily. Hourly surface forecasts have been provided on the web since September, 2002.

8.

WRF case-study evaluation and testing: WRF forecasts for IHOP cases

9.

Organized cloud systems and large-scale dynamics: Diurnal cycle of precipitation

With the support of the NCAR Initiative program, Moncrieff and Liu sought to improve the understanding and prediction of the diurnal cycle of the water cycle across the Continental U. S. NWP models have difficulty predicting space-time distribution of precipitation originating from convection oSimulations suggest that the diurnal propagation of precipitation can be captured in a cloud system resolving model.

10.

Cloud systems and microphysical processes: Microphysical properties of optically thin clouds

11.

Entrainment rates in nocturnal marine stratocumulus: Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) experiment

Stratocumulus clouds are a persistent feature over subtropical oceans where the underlying ocean is colder than the atmosphere. CYCOM-II data was obtained as a basis for comparison with predicted entrainment rates. Initial analysis, by Lenschow, Moeng, and colleagues, indicates that observed entrainment rates are less than modeled rates when the cloud layer is observed to be unstable for mixing with free-tropospheric air. This is important in study of stratocumulus clouds over subtropical oceanic regions, since stratocumulus clouds have long been recognized as having a significant impact on the radiative balance of the Earth, and thus on the Earth's climate.

12.

Surface-Atmosphere Interactions: Influence of soil moisture heterogeneity on the planetary boundary layer (PBL)

An important goal in mesoscale research is to understand the influences of surface heterogeneity surface-atmosphere interactions. Edward Patton (long-term visitor, Penn State), Peter Sullivan, and Chin-Hoh Moeng used their clear-PBL large-eddy simulation (LES) code, which was recently coupled to the NOAH (National Center for Environmental Prediction/ Oregon State University/Air Force/Office of Hydrology) land-surface model, to study the PBL response to large-scale soil moisture heterogeneity (ranging from 2-30 km). In the presence of heterogeneity, the atmosphere transports moisture differently depending on the initial moisture state in the overlying atmosphere, wet versus dry. In both situations, land-surface heterogeneity induces organized motions that scale with the heterogeneity (see movies, above). However, depending on the moisture state of the overlying atmosphere, the phase-correlated component can either be the sole contributor to the vertical water vapor mixing ratio flux, or make zero contribution (see figure, above). One of the important findings of this study is that if researchers plan to use the eddy-correlation technique to measure vertical water vapor mixing ratio fluxes at a point within a region of large-scale moist or dry soil conditions, they could dramatically misestimate the vertical fluxes if they ignore the contributions to the flux from organized motions induced via heterogeneous surface forcing.

13.

Wildfire research: Atmosphere-fire simulations of wildland fires

Through the support of the NCAR Initiative program, Coen and collaborators analyzed coupled atmosphere-fire simulations of a wildland fire to show that the universally-observed elliptical shape arises from even simple experiments and are a direct consequence of fire-atmosphere interactions. As a fire, initialized as a line in 3 m/s winds, evolves it takes on a shape well-recognized in real fires, that of a bow or ellipse of fire surrounding the ignited and burned fuel. The heat produced by the fire rises in updrafts that the winds focus at the head. These updrafts draw warm air into their base from all directions, guiding the wind to flow along the flanks and focus the heat at the front. This creates a self-perpetuating shape, which interestingly is observed to be the same in grass, brush, or forest fires.

14.

Cloud chemistry process studies: Cloud chemistry photochemical box model