On the Relationships between TRMM-observed Quantities and Lightning Frequency

The availability of large samples of lightning observations from satellites provides strong motivation for quantifying relationships between satellite-observed lightning frequency and storm properties. Quantitative relationships between lightning and storm parameters, if robust, can potentially improve precipitation estimates and also help improve microphysics parameterizations in numerical models. This paper seeks relationships between TRMM-observed quantities and lightning frequency over specific weather regimes.

The advantage of using the Lightning Imaging Sensor (LIS) on TRMM is that many other parameters can be observed from the same satellite at the same time and location. These include measurements closely related to ice water content [minimum 37/85GHz polarization corrected brightness temperature (PCT)], and to the vertical profile of precipitation content (maximum radar reflectivity as a function of altitude, throughout the mixed phase region), and convective rain rate. Estimates of ice water mass (IWM) at 8 km (-20 oC) are examined for different weather regimes. This study further determines altitudes (temperatures) where radar reflectivity parameters such as maximum radar reflectivity, 35 dBZ area and 20 dBZ area are best correlated with lightning flash rate. Finally, thresholds of microwave brightness temperature and radar reflectivity related to lightning occurrence are examined.

Preliminary results for the East Asia Monsoon regime show that areas of 35 dBZ at 7-9 km, and 20 dBZ area at 10-12 km are highly correlated with lightning flash rate. Altitudes with the best correlation between radar reflectivity and lightning flash rate are slightly regime dependent. The correlation coefficient for the pre-monsoon regime peaks at a lower altitude than that for the active-monsoon/oceanic regime. In addition, the pre-monsoon regime has lower thresholds for lightning occurrence as the active-monsoon/oceanic regime, when normalized by probability of lightning.