湿Q矢量释用技术及其在定量降水预报中的应用
Wet Q Vector Interpretation Technique with Its Application to Quantitative Precipitation Forecast
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摘要: 新发展了一种湿Q矢量释用技术:利用松弛法迭代求解以非地转干Q矢量散度为强迫项的方程得到垂直运动场ω 1, 然后由ω 1计算湿Q矢量散度场, 接着再利用松弛法迭代求解以湿Q矢量散度场为强迫项的ω方程得到垂直运动ω 2, 最后由ω 2结合水汽条件进行降水量计算, 得到湿Q矢量释用降水场。结合一次典型的江淮梅雨锋暴雨过程研究表明, 湿Q矢量释用降水场对同期观测降水场水平分布特征、极端降水强度都具有一定的反映能力, 反映出湿Q矢量释用技术具备实际应用的可行性和一定合理性。将此释用技术应用于华东区域数值预报模式 (基于MM5 V3.6而建立, 以下简称MM5) 产品, 得到湿Q矢量释用定量降水预报 (QPF) 场, 其独立于模式本身输出的QPF场, 但与模式QPF场具有相同的时空分辨率。针对2004年6—8月汛期华东地区一次梅雨锋降水过程和一次登陆台风降水过程, 结合实况雨量资料, 比较分析了湿Q矢量释用QPF场和MM5模式QPF场对实际观测降水场的反映能力, 结果表明, 前者对有无降水、10.0 mm/24 h以上明显降水的反映能力明显优于后者。进一步进行预报统计检验表明, 湿Q矢量释用预报有无降水、小雨及10.0 mm/24 h以上降水的TS评分、正确率都明显高于MM5模式, 而漏报率、空报率则是前者明显低于后者。这也充分反映出湿Q矢量释用技术应用于QPF研究的有效性。最后, 探讨了数值预报产品释用技术对数值预报模式性能的依赖性, 并指出未来对湿Q矢量释用技术进一步改进的方向及其广泛应用前景。
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关键词:
- 湿Q矢量释用技术;
- 定量降水预报;
- 华东区域数值预报模式
Abstract: A new kind of wet Q vector interpretation technique is developed for the first time.In the method, the vertical motion ω 1 can be obtained by solving omega equation whose forcing term is dry ageostrophic Q vector divergence based on iterative method, whereby the wet Q vector divergence is calculated. Then vertical motion ω 2 can be obtained by solving omega equation whose forcing term is wet Q vector divergence based on iterative method. Finally, precipitable water is calculated on the basis of ω 2 and vapor, whereby wet Q vector interpretation precipitation is produced. Using a typical Changjiang-Huaihe Meiyu front heavy rainfall, the analy tic results show that the wet Q vector interpretation precipitation field has a certain ability to reflect synchronous actual rain in the context of horizontal distribution characteristic and the extreme intensity, which manifests that wet Q vector interpretation technique is feasible and rational to some extent on the basis of practical application. The technique is applied to Eastern China regional numerical prediction model (which is based on MM5 V3.6, and hereafter termed as MM5) product, whereby wet Q vector interpretation quantitative precipitation fo recast (QPF) field is obtained, which is independent of QPF field output by the MM5 itself in such a way that it has the same spatial and temporal resolutions as the latter.In a Meiyu rainfall process and a landfall typhoon rain process occurring in eastern China during June to August 2004 and combining real rain data, the abilities of the wet Q vector interpretation QPF and MM5 QPF to reflect synchronous surface precipitation are compared and analyzed.The results indicate that the reflecting abilities of the former to fair weather or rain and the rain with intensity over 10 mm/24 h are all superior to that of the latter. Furthermore, the results of forecast statistical verification show that the test scores (TSs) and forecast accuracy of the wet Q vector interpretation fo recast are obviously higher than the counterparts of the MM5 in the context of fair weather or rain, light rain, and the rain with intensity over 10 mm/24 h, on average by 20%, 40% and 60% respectively for TSs and by 6%, 3% 11% respectively for accuracy. Meanw hile, the false-alarm and miss rates of wet Q vector interpretation forecast are evidently lower than those of the MM5, which all manifest sufficiently that the application of the wet Q vector interpretation technique to QPF research is effective. At last, the dependence of the numerical predictionproduct interpretation technique on the performance of the numerical prediction model is discussed, with further modifying directions to the wet Q vector interpretation technique.That is to say, it is necessary to take into consideration the roles of orographic lifting and surface friction, at the same time, the revised wet Q vector (QM) consisting of convective vapor condensational potential heating besides synoptic scale stable vapor condensational potential heating should be considered. Additionally, the wet Q vector interpretation technique introduced in this paper is not limited to apply to Eastern China regional numerical prediction product, it also has the interpretation ability to any model prediction product as long as temperature, wind and specific humidity at conventional layers are included. It has wide application prospects. -
图 1 1991年7月6日08:00各气象要素场
(a)1 h地面实况雨量场 (单位: mm), (b) 700 hPa湿Q矢量散度场 (虚/实线代表辐合/辐散, 单位: 10-15hPa-1·s-3), (c) 700 hPa湿Q矢量释用垂直速度场 (虚/实线代表上升/下沉, 单位:Pa·s-1), (d) 1 h湿Q矢量释用降水场 (单位:mm)
Fig. 1 Several kinds of meteorological fields at 08:00 on July 6, 1991
(a)1 h precipitation in situ (unit:mm), (b)700 hPa wet Q vector divergence (dashed/solid lines represent convergence/divergence, unit:10-15hPa-1·s-3), (c)700 hPa Q* vector inperpretation vertical velocity (dashed/solid lines represent upward/ downward, unit:Pa·s-1), (d)1 h Q*vector interpretation precipitation (unit:mm)
表 1 2004年6—8月MM5模式与湿Q矢量释用华东地区降水预报的平均TS评分结果对比 (单位:%)
Table 1 The comparison between MM5 and wet Q vector interpretation in the context of average TS of predicting precipitation over eastern China from June to August in 2004 (unit :%)
表 2 2004年6—8月MM5模式与湿Q矢量释用对华东地区晴雨预报的平均检验结果对比
Table 2 The comparison between MM5 and wet Q vector interpretation in the context of average test of predicting Eastern China fair or rain from June to August in 2004
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