With the unprecedented spaceborne precipitation radar(PR),the Tropical Rainfall Measuring Mission(TRMM) satellite has collected high-quality precipitation measurements for over ten years.The TRMM/PR data are nowadays extensively exploited in numerous meteorological and hydrological fields.Yet an artificial orbit boost of the TRMM satellite in August 2001 modulated the observation parameters,which inevitably affects climatological applications of the PR data and needs to be clarified.This study investigates the orbit boost effects of the TRMM satellite on the PR-derived precipitation characteristics.Both the potential impacts on precipitation frequency(PF) and precipitation intensity(PI) are carefully analyzed.The results show that the total PF decreases by 8.3% and PI increases by 4.0% over the tropics after the orbit boost.Such changes significantly exceed the natural variabilities and imply the strong effects of orbit boost on precipitation characteristics.The impacts on stratiform precipitation and convective precipitation are inconsistent,which is attributed to their distinct precipitation features.Further analysis reveal that the increased PI of stratiform precipitation is mainly due to the decreased frequencies of light precipitation,while the semi-constant PI of convective precipitation is caused by the concurrently decreased frequencies of light and heavy precipitation.A modification is applied to the post-boost PR precipitation data to retrieve the actual trends of tropical precipitation characteristics.It is found that the PI of total-precipitation approximately keeps invariable from 1998 to 2005.The total PF has no obvious trend over tropical oceans but decreases considerably over tropical lands.
The cloud variations under subtropical high（STH） conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.
The formation of the Kuroshio large meander in summer 2004 was investigated by using the cruise data,Argo profiles data,and satellite remote sensing data.The authors validated the point that cyclonic eddies contrib-uted to the large meander.Besides,.the impacts of ty-phoons on Kuroshio meanders were also studied.From 29 July to 4 August,the typhoons stirred the ocean and up-welled the deep water,which enhanced the existed cyc-lonic eddy,and immediately made a drastic meander of the Kuroshio.Moreover,the unexpected typhoons in June 2004 also contributed to the initial meander at the Tokara Strait.The result suggests an alternative meander mecha-nism of the Kuroshio path via the typhoon-eddy-Kuroshio interactions.It is argued that typhoons accompanied with cyclonic eddies,might play crucial roles in meanders of the Kuroshio.This will provide a more comprehensive understanding of the dynamics of the western boundary flows,like the Kuroshio and the Gulf Stream,and will be useful in eddy-resolution models.
