Long-range detection of sferics over the Pacific Ocean: Thunderstorm characteristics and data assimilation into NWP models.

摘要

The waveguide between the earth's surface and the ionosphere allows very low frequency emissions generated by lightning, called sferics, to propagate over long distances. The new Pacific Lightning Detection Network (PacNet) utilizes this attribute to monitor lightning activity over the North Pacific Ocean with a network of ground-based lightning detectors.;The performance of the PacNet was assessed. Lightning detection efficiency (DE) and location accuracy (LA) model calibration procedures are detailed, and comparisons of model results with lightning observations from the PacNet in correlation with Tropical Rainfall Measuring Mission (TRMM) satellite's Lightning Imaging Sensor (LIS) are presented.;The implications of this work are that the DE and LA model output can be used in quantitative applications of the PacNet over the Pacific Ocean. For example, storms over the North Pacific Ocean are often poorly forecast due to the lack of observations over the ocean and insufficient initial conditions in numerical weather prediction (NWP) models. By virtue of the relationship between lightning and convective rainfall rates, PacNet data hold promise as input for NWP models as a proxy for latent heat release in convection.;To investigate the relationships between lightning and other storm properties, lightning data from PacNet and LIS were compared to data from TRMM's precipitation radar and microwave imager. Three years of data over the North Pacific Ocean were analyzed.;The results of the data analysis show a consistent logarithmic increase in convective rainfall rate with increasing lightning rates. Moreover, other storm characteristics, such as radar reflectivity and ice water path, show a similar logarithmic increase.;These results were utilized to assimilate lightning data from PacNet into a NWP model. A lightning data assimilation (LDA) system was programmed, which nudged the model's latent heating rates according to rainfall derived from lightning observations.;Two cases were analyzed. A rapidly deepening extratropical cyclone approaching the west coast of the U.S. was poorly forecast initially. The use of LDA improved the storm central-pressure forecast significantly. In the second case, a squall line associated with a Kona low moved over Hawaii. The location and timing of the squall line was improved using LDA.