Passive microwave imager data from the NASA TRMM and Aqua satellites can be used to diagnose storms with potential for heavy rainfall, damaging hail, or frequent lightning. Direct records of flash flood or hail events are spatially limited by the need for either stream gauges or people to observe them. Hail records in particular are biased toward populated areas and effective reporting procedures. Passive microwave ice scattering in the 37 GHz and sometimes 18 / 19 GHz channels suggests which storms do have particularly large ice hydrometeors. Strong scattering signatures, also in the 85 / 89 GHz channels, are also associated with extreme convective-scale rain rates and frequent lightning. As such, flash flood, damaging hail, and frequent lightning hazards can be inferred. Microwave-based criteria will be set to identify the storms that do pose a substantial hazard from damaging hail, heavy rainfall, or lightning. Measurements from TMI (aboard TRMM), AMSR-E (aboard Aqua), and possibly SSM/I (aboard multiple DMSP satellites) will be compiled to objectively map potential hazardous convective weather events on a nearly global basis. Methods include simply identifying extremely low brightness temperatures in convective systems, and also applying a more detailed "Virtual Radar" algorithm to retrieve radar-like properties from microwave imager data. The Virtual Radar algorithm has been developed from TRMM data and will be expanded here to apply to other microwave imagers. This will prepare for possible application to the various microwave imagers of the future Global Precipitation Mission. Environmental conditions taken from the NCAR / NCEP Reanalysis will be associated with each event, and with events which fail to meet the criteria for hazardous convective weather. Following the approach of previous studies that have relied upon reports of significant severe weather in the United States, environmental conditions that favor hazardous convective weather will be objectively identified. While this satellite-based study introduces uncertainty by inferring characteristics from a column-integrated measure over a relatively large (by convective standards) footprint, it allows consideration of storms in areas without effective reporting networks for hazardous weather. Ultimately, this objective identification of environmental conditions associated with hazardous convective weather can suggest whether regional climate changes should be expected to increase or decrease the hazards from flash flooding, hailstorms, or lightning.
