The Weather Research and Forecasting (WRF) model is used to test the sensitivity of simulations of Hurricane Ivan (2004) to changes in horizontal grid spacing for grid lengths from 8 to 1 km. As resolution is increased, minimum central pressure decreases significantly (by 30 hPa from 8- to 1-km grid spacing), although this increase in intensity is not uniform across similar reductions in grid spacing, even when pressure fields are interpolated to a common grid. This implies that the additional strengthening of the simulated tropical cyclone (TC) at higher resolution is not attributable to sampling, but is due to changes in the representation of physical processes important to TC intensity. The most apparent changes in simulated TC structure with resolution occur near a grid length of 4 km. At 4-km grid spacing and below, polygonal eyewall segments appear, suggestive of breaking vortex Rossby waves. With sub-4-km grid lengths, localized, intense updraft cores within the eyewall are numerous and both polygonal and circular eyewall shapes appear regularly. Higher-resolution simulations produce a greater variety of shapes, transitioning more frequently between polygonal and circular eyewalls relative to lower-resolution simulations. It is hypothesized that this is because of the ability to resolve a greater range of wavenumbers in high-resolution simulations. Also, as resolution is increased, a broader range of updraft and downdraft velocities is present in the eyewall. These results suggest that grid spacing of 2 km or less is needed for representation of important physical processes in the TC eyewall. Grid-length and domain size suggestions for operational prediction are provided; for operational prediction, a grid length of 3 km or less is recommended.

The respiratory epithelium is a dynamic interface between the outside environment and the interior of the host (20, 56). Protection against respiratory infection is provided by the physical barrier formed by alveolar epithelial cells (AECs), which also are vital for maintaining lung homeostasis. AECs are abundant in number and line the pulmonary airways and alveoli. Alveolar type I (ATI) cells are the epithelial component of the thin air-blood barrier and comprise Ͼ95% of the alveolar surface area (57). Alveolar type II (ATII) cells cover approximately 4% of the mammalian alveolar surface but constitute 15% of all lung cells (8,9,20,35,57).

One of the important goals of NASA's Cirrus Regional Study of Tropical Anvils and Cirrus LayersFlorida Area Cirrus Experiment (CRYSTAL-FACE) was to further the understanding of the evolution of tropical anvil clouds generated by deep convective systems. An important step toward understanding the radiative properties of convectively generated anvil clouds is to study their life cycle. Observations from ground-based radar, geostationary satellite radiometers, aircraft, and radiosondes during CRYSTAL-FACE provided a comprehensive look at the generation of anvil clouds by convective systems over South Florida during July 2002. This study focused on the relationship between convective rainfall and the evolution of the anvil cloud shield associated with convective systems over South Florida on 23 July 2002, during the CRYSTAL-FACE experiment. Anvil clouds emanating from convective cells grew downwind (to the southwest), reaching their maximum area at all temperature thresholds 1-2 h after the active convective cells collapsed. Radar reflectivity data revealed that precipitation-sized anvil particles extended downwind with the cloud tops. The time lag between maximum rainfall and maximum anvil cloud area increased with system size and rainfall. Observations from airborne radar and analysis of in situ cloud particle size distribution measurements in the anvil region suggested that gravitational size sorting of cloud particles dispersed downshear was a likely mechanism in the evolution of the anvil region. Linear regression analysis suggested a positive trend between this time lag and maximum convective rainfall for this case, as well as between the time lag and maximum system cloud cover. The injection of condensate into the anvil region by large areas of intense cells and dispersal in the upper-level winds was a likely explanation to cause the anvil cloud-top area to grow for 1-2 h after the surface convective rainfall began to weaken. In future work these relationships should be evaluated in differing regimes of shear, stability, or precipitation efficiency, such as over the tropical oceans, in order to generalize the results. The results of this study implied that for these cloud systems, the maximum in latent heating (proportional to rainfall) may precede the peak radiative forcing (related to anvil cloud height and area) by a lead time that was proportional to system size and strength. Mesoscale modeling simulations of convective systems on this day are under way to examine anvil evolution and growth mechanisms.

No abstract