Atmospheric Water Budget Research Articles

Evaluation of the Atmospheric Water Budget Following an Intense Cold-Air Outbreak over the Gulf of Mexico—Application of a Regional Forecast Model and SSM/I Observations

Abstract The atmospheric water budget is examined for a 12-day period following an intense cold-air outbreak over the Gulf of Mexico. Budget terms are compared using analyses from the U.S. National Meteorological Center's operational Nested Grid Model (NGM) and using precipitable water and surface wind speed estimated from the Special Sensor Microwave/Imager (SSM/I) instrument aboard the defense meteorological satellite F8. The atmospheric-storage term, determined from the areal-averaged total precipitable water, does not differ significantly between that obtained from the NGM and that obtained from SSM/I data. The storage increases by a factor of more than 3 during the initial five days following the passage of the surface high over the Gulf. Horizontal flux divergence of water vapor computed from the full vertical structure in the NGM output is well approximated by the substitution of the surface-700-mb mean wind and the total precipitable water for the vertical profiles along the boundaries of the atmo...

High tropical winds

Strong and persistent low-level winds blowing over the Adriatic basin are often associated with intense precipitation events over Italy. Typically, in case of moist southeasterly wind (Sirocco), rainfall affects northeastern Italy and the Alpine chain, while with cold northeasterly currents (Bora) precipitations are localized along the eastern slopes of the Apennines and central Italy coastal areas. These events are favoured by intense air-sea interactions and it is reasonable to hypothesize that the Adriatic sea surface temperature (SST) can affect the amount and location of precipitation.High-resolution simulations of different Bora and Sirocco events leading to severe precipitation are performed using a convection-permitting model (MOLOCH). Sensitivity experiments varying the SST initialization field are performed with the aim of evaluating the impact of SST uncertainty on precipitation forecasts, which is a relevant topic for operational weather predictions, especially at local scales. Moreover, diagnostic tools to compute water vapour fluxes across the Italian coast and atmospheric water budget over the Adriatic Sea have been developed and applied in order to characterize the air mass that feeds the precipitating systems. Finally, the investigation of the processes through which the SST influences location and intensity of heavy precipitation allows to gain a better understanding on mechanisms conducive to severe weather in the Mediterranean area and in the Adriatic basin in particular.Results show that the effect of the Adriatic SST (uncertainty) on precipitation is complex and can vary considerably among different events. For both Bora and Sirocco events, SST does not influence markedly the atmospheric water budget or the degree of moistening of air that flows over the Adriatic Sea. SST mainly affects the stability of the atmospheric boundary layer, thus influencing the flow dynamics and the orographic flow regime, and in turn, the precipitation pattern.