Characteristics of lightning flashes with exceptional illuminated areas, durations, and optical powers and surrounding storm properties in the tropics and inner subtropics

摘要

Twelve years (1998-2009) of Lightning Imaging Sensor (LIS) observations are used to characterize lightning flashes by illuminated area, duration, and optical power, particularly for exceptional flashes defined as those above the 90th percentile of each parameter. Statistics of lightning are summarized over land, ocean, and coastal regions of the Tropical Rainfall Measuring Mission satellite's domain extending from 36°S to 36°N. The degree to which optical flash parameters are interrelated is discussed, as well as coincident environmental properties and the overall characteristics of parent thunderstorms. LIS flashes over the southern United States are also collocated to National Lightning Detection Network (NLDN) observations, and relationships between LIS optical flash properties and corresponding NLDN strengths are discussed. Daytime (nighttime) oceanic flashes are shown to be 31.7% (39.4%) larger and 55.2% (75.1%) brighter in terms of maximum event pixel radiance. At the same time, daytime (nighttime) coastal flashes have 22.1% (7.8%) longer durations than flashes over land and 15.6% (11.4%) longer durations than oceanic flashes. Particularly, large and bright flashes observed by LIS are typically centered in weak storm regions, but thunderstorms with exceptional flashes are, themselves, more intense overall than those with only small and dim flashes. Diurnally, the top 10% brightest lightning flashes peak about 2 h earlier than the top 10% largest and long-lasting flashes over land, implying that lightning flash characteristics vary with the life cycle of thunderstorms. Larger and more radiant flashes are also shown to be associated with stronger NLDN flashes of positive and negative polarity. Key Points Flashes over the ocean are larger and brighter than flashes over land. Large flashes often occur in weak storm regions. Storms with exceptional flashes are nonetheless larger and stronger.