THE STUDY ON THE RELATIONS BETWEEN MOISTURE FLUX IN EAST ASIA AND THE SOUTH CHINA SEA SUMMER MONSOON

We analyze the pentad average moisture flux (qv) and the monsoon intensity and get some results:strengthening periods of monsoon are all accompanied by increasing of moisture flux and extending to the high level,and moving of moisture flux convergence from west to east in the bottom layer.There are two high value centers in South China Sea (SCS) and the Yangtze River Basin.In the last dekad of July,the high moisture flux centers in SCS alternates with the Yangtze River Basin,and it is the time for moving of rain band to the north.In the years of strong monsoon,the moisture flux anomalies are positive from Indian Ocean to SCS,and the others are negative from north of SCS to Yangtze River and the southeast of North China.The convergence area of moisture vector is in easterly.In the years of weak monsoon,the anomaly distribution is opposite to the years of strong monsoon.

Variability of Summer Atmospheric Moisture Flux and Its Effect on Precipitation over East China

Using the in-situ precipitation and NCEP/NCAR daily reanalysis data, we foundby studies of change of moisture flux and its effect that the northward water vapor transportrepresented by moisture flux in East China tends to retreat southward, and the eastward water vaportransport tends to weaken with weakening of the intensity of moisture flux. The north boundary ofmeridional moisture flux (50 kg m^(-1)s^(-1)) retreats 2.8 degrees in latitude per decade during1968-2003. The weakening of water vapor transport implies the weakening and southward retreat ofEast Asian monsoon, which leads to the tendency of decrease in moisture flux convergence over NorthChina and the middle and lower reaches of the Yellow River, and the tendency of decrease inprecipitation over those regions, but on the contrary the enhanced water vapor transport convergenceover the middle and lower reaches of the Yangtze River implies the tendency of increase inprecipitation to some extent. Indeed the long-term variability of precipitation in East China has aclose relation with that of atmospheric moisture flux.

Effect of Counter-Gradient in the Computation of Turbulent Fluxes of Heat and Moisture in a Regional Model

The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gradient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.

Moisture Transport over the Arabian Sea Associated with Summer Rainfall over Pakistan in 1994 and 2002

In this study, we aimed to elucidate the critical role of moisture transport affecting monsoon activity in two contrasting summers over the Arabian Sea during the years 1994, a relatively wet year, and 2002, a relatively dry year. A comprehensive diagnostic evaluation and comparisons of the moisture fields were con- ducted; we focused on the precipitation and evaporation as well as the moisture transport and its divergence or convergence in the atmosphere. Monthly mean reanalysis data were obtained from the National Centers for Environmental Prediction （NCEP-I and -II）. A detailed evaluation of the moisture budgets over Pak- istan during these two years was made by calculating the latent energy flux at the surface （E - P） from the divergence of the total moisture transport. Our results confirm the moisture supply over the Arabian Sea to be the major source of rainfall in Pakistan and neighboring regions. In 1994, Pakistan received more rainfall compared to 2002 during the summer monsoon. Moisture flow deepens and strengthens over Arabian Sea during the peak summer monsoon months of July and August. Our analysis shows that vertically integrated moisture transport flux have a significant role in supplying moisture to the convective centers over Pakistan and neighboring regions from the divergent regions of the Arabian Sea and the Bay of Bengal. Moreover, in 1994, a deeper vertically integrated moisture convergence progression occurred over Pakistan compared to that in 2002. Perhaps that deeper convergence resulted in a more intense moisture depression over Pakistan and also caused more rainfall in 1994 during the summer monsoon. Finally, from the water budget analysis, it has been surmised that the water budget was larger in 1994 than in 2002 during the summer monsoon.

Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Nino Events

The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.

Influence of the Eastern Pacific and Central Pacific Types of ENSO on the South Asian Summer Monsoon

Based on observational and reanalysis data,the relationships between the eastern Pacific(EP)and central Pacific(CP)types of El Niño−Southern Oscillation(ENSO)during the developing summer and the South Asian summer monsoon(SASM)are examined.The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s.While the inverse relationship between the EP type of ENSO and the SASM has weakened dramatically,the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s.The drought-producing El Niño warming of both the EP and CP types can excite anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line.Accordingly,compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent,leading to suppressed convection and decreased precipitation over these regions.Moreover,anomalously less moisture flux into South Asia associated with developing EP El Niño and significant northwesterly anomalies dominating over southern India accompanied by developing CP El Niño,may also have been responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods,respectively.El Niño events with the same“flavor”may not necessarily produce consistent Indian monsoon rainfall anomalies,while similar Indian monsoon droughts may be induced by different types of El Niño,implying high sensitivity of monsoonal precipitation to the detailed configuration of ENSO forcing imposed on the tropical Pacific.