Using satellite observed total lightning and overshooting tops to diagnose convectively-induced aviation hazards over the ocean

Since there are few surface-based radar and/or other meteorological observations covering most of the oceans, convective intensity and associated aviation hazard potential (i.e., turbulence, icing, lightning) are typically evaluated using satellites. With the planned launch (2015) of the Geostationary Observational Environmental Satellite Series-R (GOES-R) satellite, two new instruments with enhanced capabilities will be available for the detection of aviation hazards in typically data spare regions: the Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM). GLM will provide the first continuous geostationary satellite-based observations of total lightning for operational applications. Ultimately, the goal is a combined GOES-R GLM/ABI algorithm for the detection of aviation hazards associated with convection. Such an algorithm should improve aviation routing and safety in the vicinity of thunderstorms, thus reducing the number of related incident reports (e.g., severe turbulence and passenger injuries during United Flight 967 over the Midwest on 20 July 2010) and suspected storm-related accidents (e.g., crash of Air France Flight 447 over the Atlantic on 1 June 2009).

As a preliminary step toward a combined GLM/ABI aviation hazard algorithm, the objective of this study is to improve our understanding of the relationships between infrared (IR) and total lightning proxies of convective intensity and hazard potential. For GOES-R ABI and GLM proxy data, we employ low-earth orbit satellite observations from the Visible and Infrared Scanner (VIRS) and Lightning Imaging Sensor (LIS) instruments, respectively, aboard the NASA Tropical Rainfall Measuring Mission (TRMM). To get a broader picture and independent validation of convective intensity, observations from the TRMM Microwave Imager (TMI) and Precipitation Radar (PR) instruments are also used.

Overshooting tops (OTs), which are traditional geostationary satellite proxies of convective intensity, are detected using a new infrared-only technique (Bedka et al. 2010) applied to VIRS 10.8 μm channel cloud-top temperatures. Past research indicates that OTs occur above strong convective updrafts: the wider and deeper the OT, the stronger the updraft. The total lightning data from LIS, which is the legacy instrument upon which GLM is based, provides another well studied metric of updraft intensity. Strong updrafts within the mixed-phase zone provide the necessary conditions within a storm for the production of lightning. Total lightning flash rates are closely associated with convective vigor and severe weather. However, the relationships between these two convective intensity metrics (OTs and total lightning) and, more importantly, aviation hazards are less well understood, especially over the oceans.

The integration of VIRS data into a new TRMM convective cell database (Leroy and Petersen; also presented at this conference) that uses TMI, PR, and LIS provides the necessary satellite data with which to characterize these relationships. The cell database includes 5 years of data from 2002 to 2006 and will be employed over a variety of ocean (Gulf of Mexico, Caribbean, North Atlantic, and South Atlantic) and land (Southeast United States, South-central US, Central America, and northern portion of South America) regions in the overlap between TRMM and GOES-R domains. When available, OT- and lightning-based intensity metrics will be compared to turbulence occurrence as determined by Eddy Dissipation Rate (EDR) data from the NCAR turbulence algorithm applied to United Airlines Boeing 757 navigation data. Pilot reports (PIREPS) of convective hazards (turbulence, icing, thunderstorms) will also be used to evaluate the utility of OT- and lightning-based convective intensity metrics. Regional, land-ocean and seasonal variability in these relationships will be explored.