Numerical studies of the air-sea interaction processes in intense tropical systems using the Coupled Ocean/Atmosphere Mesoscale Prediction System.

摘要

The purpose of this study is to further our understanding of the air-sea interaction processes in intense tropical systems through numerical modeling. Three well-documented intense tropical systems are selected to study several aspects of the air-sea processes. First, the ocean response (one-way interaction) to an idealized representation of Hurricane Gilbert (1988) using the GFDL's Modular Ocean Model version 2 (MOM2) is given. Then the two-way interactions between a TOGA COARE squall line and the tropical ocean in an idealized setting using the NRL's original Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) are shown. Finally, the mutual responses between Hurricane Opal (1995) and a Warm Core Eddy (WCE) in the Gulf of Mexico using a more recent version of COAMPS, of which the MOM2 is used as an oceanic component, are presented.; Results show that the Hurricane Gilbert increases the local speed of Loop Current over 55%. The maximum increase of WCE F surface current speed is approximate 133%. The near-inertial oscillation in the WCE F persists for at least 7 IP and propagated downward to 400 m. With the effect of Gilbert, the simulated translation of WCE F to the Mexican coast is more realistic. With the WCE F effect, the storm-induced surface current speed reduces by about 50%. The near-inertial oscillation and the vertical structure in the along-track direction are also influenced. The storm-induced sea surface temperature (SST) decrease in Gilbert's wake is over 2.5{dollar}spcirc{dollar}C.; The simulated TOGA COARE squall line from idealized conditions reproduces most of the features as observed. The squall line-induced SST decrease is about 0.21{dollar}spcirc{dollar}C, resulting in about 10% less surface heat fluxes and weaker convective motions.; The coupled system using real data is capable of reproducing the observed Hurricane Opal intensity. The simulated track is located directly over the simulated WCE. Maximum induced SST cooling behind the storm is 2{dollar}spcirc{dollar}C, whereas this cooling is significantly less over the WCE due to deeper warmer layers. The induced surface currents with a maximum of 200 cm s{dollar}sp{lcub}-1{rcub}{dollar} are characterized by near-inertial oscillations superposed on the anticyclonic circulation around the WCE. In addition, other features of the response are: (1) The WCE is responsible for 60% of the Opal's intensification; (2) The maximum surface sensible and latent heat flux amounts to 2842 watt m{dollar}sp{lcub}-2{rcub}{dollar}; (3) Opal extracts 40% of the available heat capacity (temperature greater than 26{dollar}spcirc{dollar}C) from the WCE; and, (4) The negative feedback of the induced SST cooling to Hurricane Opal is smaller with the WCE than without the WCE due to the relatively large heat content in the WCE.; Overall, the results indicate that the ocean plays an important role in controlling the intensity of the tropical systems; and the tropical systems exert large forcing to the ocean and modify the ocean requiring a long time to recover. It is necessary to use a coupled modeling system in hurricane forecast, especially in the region with large spatial variations of upper ocean thermal content. The results also indicate the needs of the development of advanced ocean data assimilation procedures in the future version of COAMPS.