Initial Studies with the Lightning Detector on the C/NOFS Satellite, and Cross Validation with WWLLN

Abstract

he lightning detector (LD) on the Communications/Navigation Outage Forecast System (C/NOFS) satellite uses a pair of silicon photodiodes, viewing each flank at right angles to the satellite track over an extended field of view. The data product is a report every ½ s of the number of digitizer cycles (125 ?s each) for which the detected power was in predefined ranges. The performance of this system over the first 2.5 years of the C/NOFS mission is discussed, statistics of its lightning observations are presented, and a statistical cross validation using the World-Wide Lightning Location Network (WWLLN) as a ground truth is provided. It is found that the LD reports of lightning, despite their blunt timing (½ s), show correlation with strokes detected and located by WWLLN. The irradiance of these strokes lies on the high-power flank of the irradiance distribution seen earlier by the FORTE satellite. Thus, the LD thresholds favor high-power lightning; it is shown that the closest portion of the field of view is more likely to provide WWLLN coincidences than is the furthest portion of the field of view. Statistics of lightning incidence are examined at low latitudes, versus longitude, and distributions that are consistent with those established earlier by the OTD and LIS instruments are retrieved. Finally, the longitude dependence of the irradiance per stroke is examined and the ways in which it differs between the three major lightning ?hot spots? is explored. It is observed that the radiance per stroke over the Congo Basin is lower than that over the other two hot spots (Maritime Continent/South Asia and the Americas), consistent with earlier observations by the OTD imager.