National Aeronautics and Space Administration

National Climate Assessment

NASA National Climate Assessment (NCA) Activities

NASA Indicators Solicitation Proposals

Development and Testing of Potential Indicators for the National Climate Assessment

Lead PI and Center: William Koshak, Marshall Space Flight Center
Title: Indicators Derived From TRMM/LIS Satellite Lightning Observations

Lightning observations from the Tropical Rainfall Measuring Mission (TRMM) satellite Lightning Imaging Sensor (LIS) will be used to obtain important lightning-based indicators for the National Climate Assessment (NCA). This effort complements and expands upon a NCA effort already in progress by the PI (Koshak) that employs national ground-based lightning detection network data to track various characteristics of cloud-to-ground (CG) lightning, and its impacts. Because LIS observations provide total lightning (i.e., both CGs and cloud flashes) extending back to 1997, our proposed effort will provide a more comprehensive assessment of the coevolution of global temperature, lightning, and adverse lightning-caused impacts on the US. According to a conservative estimate in the literature, a 40 ± 14 % increase in total lightning is anticipated per 1 degree C average land wet-bulb temperature change. Moreover, increasing global temperatures have the potential to produce not only more thunderstorms, but more intense thunderstorms across the US. Total lightning observations provided by TRMM/LIS are well-suited to observe these fluctuations across the southern half of the country (the southeastern portion of which contains the most lightning in the US). In addition, lightning nitrogen oxides (LNOx) indirectly influences our climate since it controls the concentration of ozone and hydroxyl radicals in the atmosphere, and since it is the most important source of nitrogen oxides in the upper troposphere. In turn, the distribution of ozone forcing can have a substantial influence on regional rainfall patterns.

The LIS-based indicators that we will monitor and trend include the Lightning Frequency Indicator (LFI) and the Lightning NOx Indicator (LNI). The LNI depends on flash frequency, flash area, and flash brightness; increases in any of these three variables imply an increase in LNOx production. The information provided by the LNI will be augmented using detailed regional estimates of LNOx obtained from the NASA MSFC Lightning Nitrogen Oxides Model (LNOM) data archive. The application of these key indicators in this proposed effort represents a high priority to the NCA and is a "low hanging fruit."

We will also monitor/trend two additional indicators that are derived by combining national CG lightning data with rainfall measurements from the national radar mosaic. The first indicator is the Intense Convection Indicator (ICI). By definition, we say that "intense convection" occurs whenever the product of total rainfall (in millimeters) and total number of CG strokes exceed a certain threshold for a specified grid cell and period. It allows us to monitor, by proxy, the evolution of the number of intense thunderstorms that are often, but not necessarily, accompanied by floods, hailstones, and tornados. The second indicator is the Dry Lightning Indicator (DLI). It is computed for each grid cell and period by dividing the total number of CG strokes by the rainfall amount (when the rainfall amount is below a specified value). Since "dry lightning" (i.e., CG lightning accompanied by little or no rainfall) is important to wildfire ignition, the trending of the DLI will be of value to decision makers in the Forestry sector.