Contribution of intraseasonal oscillation to long-duration summer precipitation events over southern China

Precipitation events spanning multiple days may have consequences different from those limited to a single day.In the present paper,the authors analyze circulation anomalies and precursory signals associated with long-duration（over 14 days） summer precipitation events over southern China.The results show that the over-14-day precipitation events are induced by an anomalous lowertropospheric（850-hPa） cyclone over the South China Sea（SCS） and southern China.The anomalous westerly winds to the south of the anomalous cyclone can be traced to north of New Guinea 30 days before.To the north of anomalous westerly winds,anomalous easterly winds appear later.The anomalous westerly and easterly winds form a cyclonic anomaly,moving northward and slightly westward during the following days and eventually controlling the SCS and southern China.The northward movement of anomalous westerly and easterly winds can also be found in the 30-60-day filtered wind field.This implies that the northward propagating 30-60-day intraseasonal oscillation from the equatorial western Pacific has an important contribution to over-14-day precipitation events over southern China.

Origins of intraseasonal rainfall variations over the southern South China Sea in boreal winter

This study investigates the origins of intraseasonal rainfall variations over the southern South China Sea（SCS） region in boreal winter.It is found that intraseasonal rainfall variations over the southern SCS have different origins on the 10-20-day and 30-60-day time scales.On the 10-20-day time scale,large rainfall anomalies over the southern SCS are preceded by strong northerly wind anomalies associated with the East Asian winter monsoon（EAWM）,by about two days.On the 30-60-day time scale,the strong EAWM-related northerly wind anomalies almost appear simultaneously with large rainfall anomalies over the southern SCS.In addition,obvious large rainfall anomalies occur over the southeastern tropical Indian Ocean about one week before the peak southern SCS rainfall anomalies.It indicates that the convection and related circulation anomalies with origins over the tropical Indian Ocean may play an important role in inducing intraseasonal rainfall variations over the southern SCS on the 30-60-day time scale,but not on the 10-20-day time scale.

Persistence of Snow Cover Anomalies over the Tibetan Plateau and the Implications for Forecasting Summer Precipitation over the Meiyu-Baiu Region

The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.

Variability of Surface Sensible Heat Flux over Northwest China

The present study documents the variability of surface sensible heat flux over Northwest China using station observations for the period 1961 2000.It is found that the afternoon and nighttime sensible heat flux variations are remarkably different.The variability of the instant flux in the afternoon is much larger than in the nighttime.The afternoon and nighttime flux anomalies tend to be opposite.The diurnal and seasonal dependence of sensible heat flux variations is closely related to the diurnal cycle of mean land-air temperature difference.The relationship of sensible heat flux with land-air temperature difference based on the instant value differs from that based on the daily mean.The present study indicates the importance for the models to properly simulate mean land-air temperature difference and its diurnal and seasonal variations in order to capture surface sensible heat flux variability over Northwest China and predicts its plausible impacts on climate.

Perspectives on the non-stationarity of the relationship between Indian and East Asian summer rainfall variations

The relationship between Indian and East Asian summer rainfall variations is non-stationary in observations as well as in historical simulations of climate models.Is this non-stationarity due to changes in effects of external forcing or internal atmospheric processes？ Whilst ENSO is an important oceanic forcing of Indian and East Asian summer rainfall variations,its impacts cannot explain the observed long-term changes in the Indian-East Asian summer rainfall relationship.Monte Carlo test indicates that the role of random processes cannot be totally excluded in the observed longterm changes of the relationship.Analysis of climate model outputs shows that the Indian-North China summer rainfall relationship displays obvious temporal variations in both individual and ensemble mean model simulations and large differences among model simulations.This suggests an important role played by atmospheric internal variability in changes of the Indian-East Asian summer rainfall relationship.This point of view is supported by results from a 100-years AGCM simulation with climatological SST specified in the global ocean.The correlation between Indian and North China or southern Japan summer rainfall variations displays large fluctuations in the AGCM simulation