In the flood season (from June to August) of 2020, Gansu Province experienced intensive precipitation with long duration and wide ranges. The performances of three global models (ECMWF, GRAPES_GFS and NCEP_GFS) and four regional models (GRAPES_3 km, GRAPES_LZ10 km, GRAPES_LZ3 km and regional model SMS-WARMS in East China) for 24-hour accumulated precipitation forecast were evaluated in this paper. The main results are as follows: (1) The ECMWF model surpassed the other two global models in forecast performance, while among regional models, the GRAPES_3 km and the SMS-WARMS were better, and the latter was more stable. (2) The regional models had lower accuracy of rain probability forecast and TS, ETS, POD than those of global models for light and moderate rain, but for rainstorms they outperformed global models; the POD and Bias of regional models for heavy rain and rainstorms were significantly higher than those of global models. (3) According to the differences of 500 hPa circulation pattern, the precipitation in Gansu could be divided into two types including subtropical high marginal type and low trough type. Four subtropical high marginal precipitation processes and three low trough precipitation processes in flood season of 2020 were tested and evaluated. For global models and regional models, they all had better capability in predicting precipitation with different magnitudes for the former type than the latter one. The ECMWF model and regional models were better than the NCEP_GFS model and the GRAPES_GFS model in predicting heavy rain and rainstorm. Among global models, the ECMWF model had the best forecast effect for the two precipitation types, and the East China regional model had the best forecast effect for the two precipitation types among regional models. (4) All the seven models had good forecasting capability for the spatial orientation of moderate and heavy rain for both rainfall types, while the forecast effect of rainfall location for subtropical high marginal type was better than that of low-trough type, but the predicted precipitation intensity was stronger than observations, especially for the center of precipitation.
Based on meteorological data including monthly maximum snow depth, snow cover days and snowfall days, the beginning and ending snowfall date, and winter average temperature, the highest and the lowest temperature, precipitation (1961-2008) obtained from 7 weather stations in Altay region, the snow cover variation was analyzed using linear trend, Mann-kendall test and R/S analytical methods.The results indicated that winter mean temperature presented significantly increasing trend, especially for the minimum temperature, and precipitation also increased. Snowfall and snow cover occurred early in September or October and ended in next April or May in most areas of Altay.The yearly mean maximum snow depth and snow cover days presented a single peak variation, and the maximum snow cover depth was in Altay station, the minimum value is in Fuhai station, snow cover days was miniimum in Fuhai and maximum in Jimunai, while snowfall days decreased from west to east. The maximum snow depth increased obviously, and the variation of snow cover and snowfall days were not so obvious, but some difference existed in spatial distribution. The snow cover days and the snowfall days decreased obviously. The abrupt change test indicated that in regional mean, the maximum snow depth changed abruptly in about 1983, which was consistent with winter precipitation change. R/S analysis indicated that the maximum snow depth, snow cover days and snowfall days would be anti-persistence in future, and the anti-persistence characteristic of mean snowfall days, the maximum snow depth in Fuhai, snow cover days in Jimunai, snowfall days in Buerjin would be strongest relatively.
Based on theMicap s charts, the EC objective analysis field and the T213 physical quantity field, the strong cold wave weather p rocess occurred in Aletai area from February 11 to 13, 2009 was analyzed and focused on causes of strong temperature dropp ing and rainfall during thisweather p rocess. The results indicated that the strong cold air coming from Nova Island and Taymyr accumulated over the west Siberia along the northeast and the north wind zone before the UralMountain ridge. Due to the cold air from northwest of UralMountain ridge attacking, the ridge went southeast and impeled the Siberia cold air going south on a large scale, which resulted in this strong cold wave over the area. Northern cold air and the warm and moist air from south branch trough converged over this area caused the strong rainfallwith the dynamic condition and the water vapor condition.
Based on 20 cm pan evaporation data of7 weather stations inwarm seaon from 1964 to 2001 (May-September) inXinjiang Aletai area, the feature of evaporation changewas analyzed using the linear trend and correlation analysismethods. On average in this area, the pan evaporation inwarm season presented remarkable decreasing trend, while itwas increasing in Fuyun, and was no obvious change in Jimunai and Buerjing. Analysis on the complete correlation coefficients ofclimate factorswith pan evaporation on regionalaverage show that low cloud amount, averagewind speed and diurnal temperature rangewere themain influencing factors resulted in pan evaporation decrease, but for different station they were different. The decrease in solar radiation might relate to the increase of low cloud amount and aerosol aswell as the other pollutants, whichmade pan evaporation decrease. The lowering ofwind speedmightbe associated with theweakening of theAsian winter and summermonsoon under the background of globalwarming.
