Analysis of PWV Derived from the GNSS CORS Stations for Determining the Onset of the Southwest Monsoon in Thailand

Abstract

This research shows a new threshold for identifying the onset of southwest monsoons using Precipitable Water Vapor (PWV) obtained from GNSS Continuously Operating Reference Stations (CORS) in Thailand by analyzing data from 2007 to 2016. It was found that PWV values for rainy days are higher than non-rainy days. The average PWV for the years 2007-2016 of CHAN station in May was used to determine the new threshold. This new threshold is met when the average value of PWV in May exceeds 58.50 mm for three consecutive days. During the ten years of the study period, the onset date calculated from this method varies by no more than 1-3 days from that calculated by the Thai Meteorological Department (TMD) method, except for 2008 and 2010, when the variance is more than three days. As for other regions namely the central region, the northeast region, and the northern region, it was found that the calculation of the onset of the monsoon season typically varies by 3-5 days.