Lightning in the Region of the TOGA COARE

Abstract

In the fall of 1992 a lightning direction finder network was deployed in the western Pacific Ocean in the area of Papua New Guinea. Direction finders were installed on Kapingamarangi Atoll and near the towns of Rabaul and Kavieng, Papua New Guinea. The instruments were modified to detect cloud-to-ground lightning out to a distance of 900 km. Data were collected from cloud-to-ground lightning flashes for the period 26 November 1992?15 January 1994. The analyses are presented for the period 1 January 1993?31 December 1993. In addition, a waveform recorder was located at Kavieng to record both cloud-to-ground lightning and intracloud lightning in order to provide an estimate of the complete lightning activity. The data from these instruments are to be analyzed in conjunction with the data from ship and airborne radars, in-cloud microphysics, and electrical measurements from both the ER-2 and DC-8. The waveform instrumentation operated from approximately mid-January through February 1993. Over 150 000 waveforms were recorded. During the year, January?December 1993, the cloud-to-ground lightning location network recorded 857 000 first strokes of which 5.6% were of positive polarity. During the same period, 437 000 subsequent strokes were recorded. The peak annual flash density was measured to be 2.0 flashes km-2 centered on the western coastline of the island of New Britain, just southwest of Rabaul. The annual peak lightning flash density over the Intensive Flux Array of Tropical Oceans Global Atmosphere Coupled Ocean_Atmosphere Response Experiment was 0.1 flashes km-2, or more than an order of magnitude less than that measured near land. The diurnal lightning frequency peaked at 1600 UTC (0200 LT), perhaps in coincidence with the nighttime land-breeze convergence along the coast of New Britain. Median monthly negative peak currents are in the 20?30-kA range, with first stroke peak currents typically exceeding subsequent peak currents. Median monthly positive peak currents are typically 30 kA with one month (June) having a value of 60 kA. Positive polar conductivity was measured by an ER-2 flight from 40°N geomagnetic latitude to 28°S geomagnetic latitude. The measurements show that the air conductivity is about a factor of 0.6 lower in the Tropics than in the midlatitudes. Consequently, a tropical storm will produce higher field values aloft for the same rate of electrical current generation. An ER-2 overflight of tropical cyclone Oliver on 7 February 1993 measured electric fields and 85-GHz brightness temperatures. The measurements reveal electrification in the eye wall cloud region with ice, but no lightning was observed.