Influence of South China Sea SST and the ENSO on Winter Rainfall over South China

The present study investigates the influence of South China Sea （SCS） SST and ENSO on winter （January-February-March; JFM） rainfall over South China and its dynamic processes by using station observations for the period 1951-2003, Met Office Hadley Center SST data for the period 1900-2008, and ERA-40 reanalysis data for the period 1958-2002. It is found that JFM rainfall over South China has a sig- nificant correlation with Nio-3 and SCS SST. Analyses show that in El Nio or positive SCS SST anomaly years, southwesterly anomalies at 700 hPa dominate over the South China Sea, which in turn transports more moisture into South China and favors increased rainfall. A partial regression analysis indicates that the independent ENSO influence on winter rainfall occurs mainly over South China, whereas SCS SST has a larger independent influence on winter rainfall in northern part of South China. The temperature over South China shows an obvious decrease at 300 hPa and an increase near the surface, with the former induced by Nio-3 and the latter SCS SST anomalies. This enhances the convective instability and weakens the potential vorticity （PV）, which explains the strengthening of ascending motion and the increase of JFM rainfall over South China.

Mesoscale Vortex Generation and Merging Process: A Case Study Associated with a Post-Landfall Tropical Depression

An observational analysis of satellite blackbody temperature （TBB） data and radar images suggests that the mesoscale vortex generation and merging process appeared to be essential for a tropical-depression-related heavy rain event in Shanghai, China. A numerical simulation reproduced the observed mesoscale vortex generation and merging process and the corresponding rain pattern, and then the model outputs were used to study the related dynamics through diagnosing the potential vorticity （PV） equation. The tropical depression （TD） was found to weaken first at lower levels and then at upper levels due to negative horizontal PV advection and diabatic heating effects. The meso-vortices developed gradually, also from the lower to the upper levels, as a result of positive horizontal PV advection and diabatic heating effects in the downshear left quadrant of the TD. One of these newly-generated vortices, V1, replaced the TD ultimately, while the other two, V2 and V3, merged due to the horizontal PV advection process. Together with the redevelopment of V1, the merging of V2 and V3 triggered the very heavy rain in Shanghai.

A Method for Diagnosing the Secondary Circulation with Saturated Moist Entropy Structure in a Mature Tropical Cyclone

Under the adiabatic, axisymmetric and steady assumption, a relationship between the saturated moist entropy structure and the secondary circulation in a tropical cyclone(TC) is derived from the continuity equation. It is found that the isentropic surfaces coincide with the streamlines, and the streamfunction can be expressed with saturated moist entropy. The secondary circulation and the saturated moist entropy structure depend on each other. Thus, a method for diagnosing the secondary circulation with the structure of saturated moist entropy is proposed. The method is verified with a simulated intense idealized TC with a highly axisymmetric structure. The diagnosed secondary circulation reproduces well the moist inflow in the boundary layer and the moist updraft in the eyewall. This method facilitates secondary circulation diagnosis in theoretical or mature TCs that satisfy the adiabatic, axisymmetric and steady approximations.

Effects of the Indo-China Peninsula Heat Fluxes on the 1998 South China Sea Summer Monsoon

Sensitivity experiments to investigate the role and importance of theIndo-China Peninsula (ICP) heat fluxes (sensible and latent heat fluxes) on the South China Seasummer monsoon (SCSSM) onset and its subsequent evolution have been carried out using a regionalclimate model. Two sensitivity experiments have been conducted: cutting off the sensible heat flux(noted as IChfx) and latent heat flux (noted as ICqfx). Results show that by cutting off theunderlying heat flux of the ICP, the precipitation decreases and low-level geopotential heightincreases over the local regions as well as the remote regions of the East China Sea, southernJapan, and western North Pacific. The westerly (easterly) zonal winds at 850 hPa (200 hPa) aregenerally weakened in May and June, especially before and during the onset of the SCSSM towards theend of May. It is worth noting that although the observed sensible heat flux is only about 1/3 ofthe latent heat flux, the differences between the control run and each of the two sensitivityexperiments are comparable.