Sunday, 22 January 2012
Moisture Transport Measurements Using Ground Based GPS and Their Relation to Topographically Modified Sea Breeze Circulation At Mayaguez, Puerto Rico
Hall E (New Orleans Convention Center )
analysis of sea breeze occurrences was done during the SEAR (Senior Experience in Atmospheric Research) campaign in Mayaguez, Puerto Rico from March 15th through the 31st 2011 to consider the unique topographic influences on moisture advection. This study used surface observations in combination with ground based GPS measurements of precipitable water and Weather Research and Forecasting (WRF) model forecasts. Both of these were statistically verified to quantify their accuracy. It was found through analysis of observations and the WRF model streamlines that local wind patterns are often a result of a balancing between thermally driven sea breeze circulations and island wake in the form of dual rotating gyres on the leeward side of the island. Either sea breeze or the gyres may cause westerly wind shifts leading to onshore flow. Thermally driven sea breeze occurs only when the synoptic scale winds are oriented favorably to produce the gyres, however on shore flow can occur when gyres are present even when the thermally driven sea breeze does not reach the coast. We investigate the improvement in forecasting on shore flow that can be achieved by considering the Froude number in addition to the Sea Breeze Index (SBI). Precipitable water measurements indicated moisture increases by more than 1cm in the on shore flow period due to synoptic scale changes that allow moisture from lower latitudes to reach Puerto Rico. There is some indication that the peak in the diurnal variation of PW is higher for sites on the western side of Puerto Rico during times with high SBI compared to periods of on shore flow when gyres are the dominant forcing. There is a large variation in the vertical moisture due to elevation differences in the steep topography of Puerto Rico that must be considered in order to see clear variations due to advection.