Second Annual AMS Student Conference


Sea Breeze and Local Wind Effects on Rainfall in South Florida

Ryan T. Ellis Sr., Univ. of Miami/RSMAS, Miami, FL

Sea breeze circulation plays a significant role in precipitation forecasting in South Florida. Current numerical forecast models are often deficient in recognizing a sea breeze signal due to relatively low grid resolution and inadequate model physics. The objective of this study is, to understand the physical processes associated with precipitation caused by sea breeze circulation by using a high-resolution nested grid model to resolve sea breeze and local wind patterns in the numerical model. This will allow us to better understand convection associated with the sea breeze and, finally, to improve local and quantitative precipitation forecasts. In this study, the impact of model grid resolution on precipitation forecasts in South Florida is evaluated. Using the nonhydrostatic, high resolution PSU/NCAR MM5 model, numerical simulations have been run at 2-km resolution for the month of June 1999 with a domain spanning the east and west coasts of South Florida including the Lake Okeechobee region. NEXRAD ground based radar imagery and the MM5 both depict that precipitation associated with sea breeze occurred on nearly half of the days for the month. At 2-km resolution, model runs indicate a clear sea breeze signal that propagates inland. Examining the wind perturbation fields, we found that the magnitude of the sea breeze composes nearly 20% of the daily mean. Perturbation fields also show that high-resolution MM5 is capable of resolving a lake breeze effect 15 to 20 km inland at a magnitude of close to 3 m s-1. Vertical wind profiles show that the vertical extent of sea breeze circulation is typically from the 15 to 2000-m level. Model images are compared against NEXRAD ground based radar-derived rainfall totals and surface observations at various points along both coasts as well as the lake region. Preliminary results show that the higher model resolution improves model forecasts with respect to patterns of rainfall associated with sea breeze and local winds. Quantitative precipitation forecasts are also very sensitive to model resolution as the 12-km resolution run of the MM5 was unable to sense sea breeze circulation patterns

Poster Session 2, Weather/Forecasting
Sunday, 9 February 2003, 5:30 PM-7:30 PM

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