Compact Intracloud Discharge Locations Compared To Thunderstorm Radar Echo Structure

Abstract:

In this presentation we study positive polarity Compact Intracloud Discharges (CIDs), which are also known as Narrow Bipolar Pulses (NBPs). Positive NBPs are classified according to their location, found using a three-dimensional time-of-arrival method, within the thundercloud radar echo. Using NEXRAD radar data, the NBPs are classified as occurring (1) in the Updraft region, (2) Outside of the Updraft region, or (3) in the Anvil region. Total of 177 positive NBPs found on one storm day in several Florida storms were analyzed and categorized into the above groups. A large majority of the NBPs occurred in the Updraft region (over 80%), while about 15% occurred in Outside of the updraft region and only few percent occurred in the Anvil region. The NBPs were more common in or above high radar reflectivity regions ≥ 30 dBZ, yet many were associated with ≤ 30 dBZ and even ≤ 20 dBZ regions. There are also cases of re-occurrence of an NBP in close proximity (within 500 m in x and y position) to previous NBP locations: 38 of these re-occurrences were doublets, and there were seven triplets present. One case with four very close (within about 350 m horizontally and with only 23 - 494 s time separation) proximate occurrences can be seen in our data set. Recently Karunarathne et al. [2014] have identified three main types of NBPs according to their electromagnetic wave shapes as (a) clean bipolar, (b) those with secondary peaks and (c) those with faster rise time and longer duration. In this study, the presence of these wave shape types within the updraft, outside of the updraft and the anvil region are analyzed. The majority (over 50 %) of the NBPs in the updraft region comprised with type (b) NBPs. Outside of the updraft and the anvil contained majority of type (c) NBPs. Outside of the updraft, only a very few type (a) NBPs are found among this set of 177 examples.