中亚5月土壤湿度异常对6月降水的影响

Influences of soil moisture anomalies in May on June precipitation in Central Asia

利用1980—2019年欧洲中期天气预报中心提供的ERA5月平均再分析数据和全球降水气候中心(GPCC)提供的逐月降水数据,分析中亚前期5月土壤湿度异常对后期6月局地降水变化的影响。结果表明:(1)中亚春季逐月土壤湿度总体表现为北部和中部高、西南和东南低的空间分布特征;3—4月土壤湿度年际变化的大值区主要位于中亚西南部;中亚北部土壤湿度在3月呈显著增加趋势,4—5月显著减少;中亚西南部3月土壤湿度显著减少。(2)中亚中部地区5月土壤湿度异常与当地6月的降水变化呈显著正相关,通过95%信度检验。5月土壤湿度正异常可以持续到6月,导致6月局地蒸发量增加,大气可降水量增多;同时地表向上潜热通量增加、感热通量减少、波恩比减小,进而导致大气边界层降低、低层大气湿熵增加、对流不稳定能量增大,有利于降水天气的发生。(3)前冬Ni?o3.4指数与中亚中部地区次年5月土壤湿度和6月降水异常都呈显著正相关,5月土壤湿度是厄尔尼诺-南方涛动(ENSO)影响次年6月中亚中部地区降水异常的重要媒介,但土壤湿度可独立于ENSO影响6月降水。

Using RA5 monthly reanalysis data from the European Centre for Medium-Range Weather Forecasts and monthly precipitation records from the Global Precipitation Climatology Centre spanning 1980 to 2019,this study examines the influence of May soil moisture anomalies on subsequent June precipitation variability in Central Asia.The findings unveil the following key insights:(1)The spatial distribution of springtime soil moisture exhibited elevated levels in Central Asia’s northern and central regions and lower levels in the southwest and southeast.Maximum standard deviations occurred in southwest Central Asia during March and April.In the north of Central Asia,soil moisture experiences a noteworthy increasing trend in March but displays a declining trend from April to May.Conversely,southwest Central Asia witnessed substantial decreases in March.(2)June precipitation in Central Asia positively correlates with local soil moisture in May.Persistent wet soil moisture anomalies from May to June contribute to increased atmospheric precipitable water,modifying regional evaporation patterns in June.Heightened evaporation leads to increased latent heat flux and reduced sensible heat flux.A small Bowen ratio indicates a relatively shallow boundary layer that promotes low-layer moist entropy and a heightened potential for convective activity.Consequently,June rainfall over the central regions of Central Asia increased.(3)A notable positive correlation exists between soil moisture in May and precipitation in June over middle Central Asia and the preceding winter Niño3.4 index.The influence of the preceding El Nino-Southern Oscillation(ENSO)on June precipitation in middle Central Asia is mediated by May soil moisture.Nonetheless,soil moisture anomalies can independently impact the variability of June precipitation,separate from the influence of ENSO.