Abstract
Lightning network data, considered as a useful supplement to radar observations, are a good indicator of severe convection, and has high temporal and spatial resolution. In Numerical Weather Prediction (NWP) models, lightning data are a new source of data to improve the forecasting of convective systems. In this case study, lightning data assimilation is conducted by converting lightning data to water vapor mixing ratio via a simple smooth continuous function, with input variables of total flash rate and simulated graupel mixing ratio at 9 km gridded resolution. Relative humidity converted from the retrieved water vapor mixing ratio is assimilated into the background field utilizing the three-dimensional variational (3DVAR) method in WRFDA (the Weather Research and Forecasting model Data Assimilation system). The benefits of assimilating lightning data are demonstrated in a series of experiments using data from a strong convection event that affected Beijing, Tianjin, Hebei and Shandong Province, on 31 July 2007. A nested domain with resolutions of 9 km and 3 km is implemented. For this case, assimilating lightning data shows some improvements in predictions of both reflectivity and neighboring precipitation, and in the temperature, dew-point temperature and relative humidity profile after seven hours.
Highlights
IntroductionElectric charges are carried by ions and hydrometeors
Lightning is a common discharge phenomenon in convective weather
The results showed that the nudging method had considerable promise for routinely improving short-term (≤6 h) forecasts of high-impact weather with convection-allowing forecast models
Summary
Electric charges are carried by ions and hydrometeors. It is well established that the non-inductive process is the dominant electrification mechanism in convective clouds [1,2]. In the supercooled environment in convective clouds, small ice crystals grow owing to vapor diffusion and accretion of supercooled water droplets. During elastic collisions between more or less rimed particles in the supercooled environment, charges are exchanged between the colliding particles. As the non-inductive process occupies the leading role, charges of opposite polarities separate in rebounding collisions between growing graupel pellets. (a); and and analyzed analyzedfields fields for(b) (b)Exp. Exp.Radar;(c). 1.5 km) at li_ra for wind li_ra for wind (m·s−1) (at level = 8, about 1.5 km) at 0300 UTC.
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