Integrated water vapor during active and break spells of monsoon and its relationship with temperature,precipitation and precipitation efficiency over a tropical site

Global Positioning System(GPS)measurements of integrated water vapor(IWV)for two years(2014 and 2015)are presented in this paper.Variation of IWV during active and break spells of Indian summer monsoon has been studied for a tropical station Hyderabad(17.4°N,78.46°E).The data is validated with ECMWF Re-Analysis(ERA)91 level data.Relationships of IWV with other atmospheric variables like surface temperature,rain,and precipitation efficiency have been established through cross-correlation studies.A positive correlation coefficient is observed between IWV and surface temperature over two years.But the coefficient becomes negative when only summer monsoon months(June,July,August,and September)are considered.Rainfall during these months cools down the surface and could be the reason for this change in the correlation coefficient.Correlation studies between IWV-precipitation,IWVprecipitation efficiency(P.E),and precipitation-P.E show that coefficients are-0.05,-0.10 and 0.983 with 95%confidence level respectively,which proves that the efficacy of rain does not depend only on the level of water vapor.A proper dynamic mechanism is necessary to convert water vapor into the rain.The diurnal variations of IWV during active and break spells have been analyzed.The amplitudes of diurnal oscillation and its harmonics of individual spell do not show clear trends but the mean amplitudes of the break spells are approximately double than those of the active spells.The amplitudes of diurnal,semidiurnal and ter-diurnal components during break spells are 1.08 kg/m^(2),0.52 kg/m;and 0.34 kg/m;respectively.The corresponding amplitudes during active spells are 0.68 kg/m^(2),0.41 kg/m;and 0.23 kg/m;.

THE APPROACH TO REMOTE SENSING OF WATER VAPOR BASED ON GPS AND LINEAR REGRESSION T_m IN EASTERN REGION OF CHINA

The approach to remote sensing of water vapor by using global positioning systems(GPS)is discussed.In order to retrieve the vertical integrated water vapor(IWV)or the precipitable water (PW),the weighted“mean temperature”of the atmosphere,T_m would be estimated to the specific area and season.T_m depends on surface temperature,tropospheric temperature profile,and the vertical distribution of water vapor.The surface temperature dependence is borne out by a comparison of T_m and the values of surface temperature T_s using radiosonde profiles of Beijing Station(No.54511)throughout 1992.The analysis of radiosonde profiles spanning a one-year interval(1992)from sites in eastern region of China with a latitude range of 20-50°N and a longitude range of 100-130°E yields the coefficients α and b of a linear regression equation T_m= α+bT_s.

Contrasting Impacts of Three Types of ENSO Event on Boreal Autumn Rainfall over Southwest China

The autumn precipitation over southwest China is one of the main causes of meteorological disasters. Using observed monthly station rainfall data and HadISST and NCEP/NCAR analysis data, the impacts of three types of El Niño-Southern Oscillation (ENSO) events on the boreal autumn rainfall over southwest China were determined. Over southwest China, autumn rainfall constitutes > 20% of the total annual rainfall and a marked decline in autumn rainfall commenced around 1990. During La Niña events, there is surplus (deficit) over the middle (northwest and southeast) of southwest China. In cnetral Pacific (CP) El Niño events, the autumn rainfall anomaly shows a deficiency over China. The large-scale atmospheric circulation anomalies in the three ENSO categories also exhibit distinct characteristics. During CP El Niño autumns, the pressure anomaly over the North Pacific Ocean displays a “” structure, with a high-pressure anomaly over the Asian continent. An anomalous cyclone appears over the western North Pacific (WNP). In EP El Niño autumns, the pressure anomaly over the North Pacific Ocean has a “” structure, with a low-pressure anomaly over the Asian continent. An anomalous anticyclone appears over the WNP and the 500-hPa anomalies are opposite to those of CP El Niño events. During La Niña autumns, the characteristics of circulation present the opposite structure to those of CP El Niño events. This work is of certain significance for an in-depth understanding of the impacts of ENSO on the autumn precipitation over southwest China.