Brief Communication An electrifying atmospheric river – understanding the thunderstorm event in Santa Barbara County during March 2019

摘要

On 5?March 2019 12:00UTC, an atmospheric river (AR) made landfall in Santa Barbara, CA, and lastedapproximately 30h. While ARs are typical winter storms in the area, the extraordinarynumber of lightning strikes observed near coastal Santa Barbara made this event unique. The EarthNetworks Global Lightning Network (ENGLN) detected 8811 lightning flashes around southernCalifornia (30 to 37°N and 130 to 115°W) in 24h, which is roughly2500 times the climatological flash rate in this region. The AR-related thunderstorm resulted inapproximately 23.18mm accumulated precipitation in 30h in Santa Barbara. Thisarticle examines synoptic and mesoscale features conducive to this electrifying AR event,characterizing its uniqueness in the context of previous March events that made landfall in theregion. We show that this AR was characterized by an unusual deep moist layer extending fromthe low to mid-troposphere in an environment with potential instability and low-elevation freezinglevel. Despite the negligible convective available potential energy (CAPE) during the peak of thethunderstorm near Santa Barbara, the lifting of layers with high water vapor content in the AR viawarm conveyor belt and orographic forcing in a convectively unstable atmosphere resulted in theformation of hail and enhanced electrification.