Wet Q Vector Interpretation Technique with Its Application to Quantitative Precipitation Forecast

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.