Poster PDF

Abstract

Accurate modeling of mid-latitude cyclones is a key to making relevant and informative forecasts, as well as understanding climate-induced changes in the Earth’s hydrologic cycle. While current models realistically simulate extratropical cyclone structure at the synoptic scale, these cyclones are also affected by processes at the meso- and microscales, such as the absorption and release of latent heat during the evaporation and condensation of water vapor. Although localized on shorter time scales, these smaller processes affect the cyclone as a whole through upscale linkages. These effects are not immediately obvious, and must be deconvolved with the help of research models, which provide a virtual laboratory to explore both intra- and interscale linkages. And, though models are significant as a standalone tool, a better sense of the entire system is possible when model results are used in combination with observational results.

Our study utilizes this dual perspective to examine the effect of latent heat release in a winter storm off the East Coast of the United States between 21-26 November 2006. This storm was sampled multiple times by various satellites in NASA’s A-Train constellation, as it remained stationary for approximately 3 days. During this time, it drew in significant amounts of warm moist air from the tropics. Given the condensation and subsequent latent heat release of the tropical air as it was drawn northward, this storm is an optimal case to isolate the effects of latent heat release on cyclone and frontal structure. To deconvolve these effects, we modeled this case with the Weather Research and Forecasting (WRF) model run at a cloud system resolving horizontal grid spacing of 4 km, under both control conditions and with latent heat release removed.  Furthermore, we have leveraged the observations of NASA’s A-Train suite of satellites in order to verify and enlighten our control model results. Using these resources, we undertook three analysis methods: Firstly, a traditional synoptic analysis, allowing for direct comparison with reanalysis and observations of the event. Secondly, we compare the differences between model runs and observations via simulated satellite data, allowing for comparison to space-borne observations such as those on the A-Train. Thirdly, we probe cyclone dynamics by conducting a potential vorticity analysis, focusing on the anomalous areas, and specific changes due to the presence of latent heat release.

We find that the surface-level pressure gradient around the low pressure center is stronger when the effects of latent heat release are removed from the model run. While the potential vorticity anomalies associated with the system are both weakened and more isolated in the no-latent heat release run, the minimum sea level pressure in both model runs is similar. Our results indicate that latent heat may not have had a large role in strengthening this particular storm. The implication is that cyclogenesis may be more sensitive to placement of latent heat release than to the total integrated amount. 

Back to top