This research focuses on enhancing understanding of the inter-relationships between the Geostationary Operational Environmental Satellite (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations, total lightning information, and polarimetric radar fields related to the mechanisms that initiate lightning within convective clouds (so-called first lightning). A hypothesis to be tested is that one can estimate the onset, intensity and character of lightning events (i.e. the relative amount of lightning expected, in terms of flash rates over time) in convective clouds across a region. Lightning within convective clouds is far from ubiquitous, and therefore considerable uncertainty exists as to why certain storms are prolific lightning producers, while others nearby may not be. The project goals are: (1) Perform basic research to relate GOES satellite-observed (infrared) convective cloud growth properties to the character (intra-cloud versus cloud-to-ground) and intensity of lightning in these clouds, and to the relationship to in-cloud dual-polarimetric Doppler radar-observed microphysical distributions; (2) Enhance understanding of convective regimes by describing the general characteristics of lightning and convective cloud development as observed by satellite and dual-polarimetric Doppler radar in various environments; (3) Extend current ability to nowcast (0-90 minutes) lightning events using GOES and MODIS.
Intellectual Merit: The research will lead to an improved understanding of the interrelationships between lightning, cloud microphysics, and of satellite observations of growing cumulus. This research will take advantage of an exiting meteorological testbed that includes dual-polarimetric radar, lightning mapping array, GOES, MODIS and Tropical Rainfall Measuring Mission (TRMM) observations, and a mobile radar. Density of lightning will be correlated in space and time to graupel, freezing altitudes and ice distributions (all inferred from polarimetric radar), and compared to GOES cloud-top cooling rates as an estimate of in-cloud vertical mass flux, cumulus cloud growth, and cloud-top microphysics. Insights into cumulus cloud electrification, recharge, and lightning types will be subsequently developed from this research.
Broader Impact: A current CI (convective initiation) forecasting technique developed by the Principal Investigators is already being evaluated within the Federal Aviation Administration's Aviation Weather Research Program and the National Weather Service. The mechanisms, therefore, are in place for this research to immediately impact a broad operational community. In addition, collaboration with other university scientists and graduate students will further extend this research to the larger academic and educational community.
Funding through NSF research grant 0813603 by PI Dr. John R. Mecikalski at the University of Alabama in Huntsville (UAHuntsville), "Collaborative Research: Understanding Relationships between First Lightning, In-cloud Microphysics and Satellite-Observed Cumulus Cloud-top Properties," has lead to the development a 0–1 hour nowcasting (short-term forecasting) capability for first–flash lightning occurrence, or also called, "lightning initiation." Lightning initiation (LI) nowcasting provides advanced notice of an initial flash of lightning from a growing convective cloud as it becomes a thunderstorm as might develop on a summer afternoon. The main method discovered to predict lightning involves processing 5–15 minute infrared satellite imagery from geostationary satellites like the Geostationary Operational Environmental Satellite (GOES) over North America or the Meteosat over Europe and Africa. The infrared fields evolve and change while cumulus clouds grow and deepen, and eventually form ice–filled anvils high in the troposphere. This evolution can be interpreted from space as strong updrafts within cumulus clouds that contain ice. The combination of strong updrafts and ice is what leads to charge separation in clouds, and the formation of lightning. Presently, lightning can only be predicted ~10-15 minutes in advance using radar data, whereas data from geostationary satellites now more than doubles this lead–time to 30–45 minutes or more. Figure 1 shows schematically how the GOES infrared fields change for clouds that eventually produce lightning flashes, from 60 min before a first flash ("LI–60" in Fig. 1) to the time of "lightning initiation" ("LI–0"). In Fig. 1, typically no cloud exists at 60 min ("LI–60" in figure) before lightning begins. Cumulus clouds appear 45 min in advance of lightning ("LI–45"), and precipitation (the gray shading) often forms within the cloud once the cloud–top temperature cools to about 273 K (or 0° C, 32° F). Lightning is denoted to initiate in clouds at LI–0. The 15–min trends in the GOES channels [3.9 µm reflectance, 6.5 µm temperature (Tb), 10.7 µm Tb and 13.3 µm Tb] are indicated by Δ. Channel differences are also used, such that the "Tb65107" to represent the 6.5–10.7 µm channel difference. Up to 10 unique infrared fields can be monitored using GOES and Meteosat data. On GOES over the U.S., these fields are various combinations of four wavelengths or channels within the infrared spectrum of radiation, specifically 3.9, 6.5, 10.7 and 13.3 microns (µm). Examples include the 13.3–10.7 µm and 3.9–10.7 µm brightness temperature (Tb) differences, and reflectance estimated from the 3.9 µm channel. These fields estimate aspects of cumulus clouds linked to thunderstorm occurrence, as noted above: cloud altitude, the presence of ice at cloud top, in–cloud updrafts.
