Showing papers by "Christopher A. Davis published in 2003"

Coherence of Warm-Season Continental Rainfall in Numerical Weather Prediction Models

Abstract: A recent study by Carbone et al. revealed “episodes” of warm-season rainfall over North America characterized as coherently propagating signals often linking multiple mesoscale convective systems over spatial scales of 1000–3000 km and timescales of 1–3 days. The present study examines whether these propagating signals are found in two numerical weather prediction (NWP) models commonly used today, namely, the Eta Model from the National Centers for Environmental Prediction and the newly developed Weather Research and Forecast (WRF) model. The authors find that the diurnal cycle of rainfall over much of the United States east of the Rockies is poorly represented, particularly over the central United States, where a nocturnal rainfall maximum is observed. Associated with this nocturnal maximum is an axis of propagating rainfall emanating from the western High Plains in the late afternoon, extending across the Midwest overnight, and occasionally continuing to the Appalachians on the second day. This...

Baroclinically Induced Tropical Cyclogenesis

Abstract: The authors investigate the transition of numerous subtropical cyclones into late season tropical storms and hurricanes during the 2000 and 2001 Atlantic tropical cyclone seasons. In all transitioning cases (10), the 900–200-hPa wind shear was initially near or in excess of the upper limit of vertical shear deemed suitable for tropical cyclogenesis. In many of these cases, the vertical shear decreased markedly near or prior to the time of tropical cyclone formation. In cases that did not become named tropical cyclones, either the tropospheric vertical shear remained in excess of 15–20 m s−1 or the underlying sea surface temperature (SST) dropped below about 26°C prior to or during the weakening of the shear. Cases in which the shear remained large featured multiple, short-wave upper-tropospheric troughs interacting with the developing lower-tropospheric disturbance such that classical occlusion did not occur. Through detailed analysis and simulation of the development of Hurricane Michael in 2000...

Incorporating TOMS Ozone Measurements into the Prediction of the Washington, D.C., Winter Storm during 24–25 January 2000

Abstract: In this study, a methodology is proposed for incorporating total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) into the initial conditions of a mesoscale prediction model. Based on the strong correlation between vertical mean potential vorticity (MPV) and TOMS ozone (O3) that was found in middle latitudes at both 30- and 90-km resolutions, using either analyses or 24-h model forecasts, a statistical correlation model between O3 and MPV is employed for assimilating TOMS ozone in a four-dimensional variational data assimilation (4DVAR) procedure. A linear relationship between O3 and MPV is first assumed: O3 = α(MPV) + β. The constants α and β are then found by a regression method. The proposed approach of using this simple linear regression model for ozone assimilation is applied to the prediction of the 24–25 January 2000 East Coast winter storm. Three 4DVAR experiments are carried out assimilating TOMS ozone, radiosonde, or both types of observations. It is found that adjustm...