Application of three-dimensional triple nested mesoscale model for assessing the transport and boundary layer variability over the Indian Ocean during INDOEX

Abstract

A three-dimensional triple nested domain version of MM5 was applied for INDOEX region (40.12°N- 32.04°S; 32.10°E-117.90°E) to study the regional flow patterns and associated transport using backward and forward trajectories. The model was integrated for 48- h period starting 00 UTC 5 March 1999. From the simulations a mapping of the temporal and spatial variations in the marine boundary layer (MBL) heights were obtained. The boundary layer heights were verified using actual ship-based sounding from RV Ronald H. Brown and a good agreement was found. The model simulated significant variability in the MBL heights both spatially and temporally. During the daytime, the continental boundary layer was ~ 1500 m deep while over the ocean, the MBL was shallow (~ 300 m) near the coast, and it increased steadily towards the ITCZ where MBL heights of ~ 1000 m were encountered. During night there was a reversal with the continental boundary layer heights averaging less than 500 m while over the ocean, particularly over the ITCZ, the MBL heights were ~ 1000 to 1500 m. This variability in the MBL heights significantly affected the transport pattern over the INDOEX region. Both the backward and forward trajectories showed distinct characteristics depending on the source region (eastern or western coastal landmass, equator, or near ITCZ). Near the coast, there was an evidence for localized circulation in which the air parcels were trapped along the coast. For the open oceans (both near the ITCZ as well as equator) the air parcel trajectories continued over a significant distance. Results suggest that MM5 can be successfully applied for diagnostic studies related to INDOEX, and that the boundary layer heights and the variations in the air parcel transport need to be considered for interpreting the surface measurements.