Observing and Understanding the Variability of Water in Weather and Climate
17TH Conference on Hydrology


Satellite Derived Convective Cloud-Top Heights using NOGAPS data


Robert H. Wade, SAIC, Monterey, CA; and S. D. Miller

The cloud-top heights product at the Naval Research Laboratory (NRL) in Monterey California provides a useful tool to the operational community by assessing convection. Convection is an important process on earth and is a major component of the water cycle as it drives water in its various forms deep into the atmosphere. Deep convection is the source of stratospheric water vapor that is significant in the Earth's radiation budget. Convection in its many forms may create substantial hazards to the aviation community. Namely, the presence of turbulence, hail, lightning, and icing are potential concerns for the safe operation of aircraft in the presence of convection. In a naval environment, thorough understanding of the convection process can assist tactical planning and the deployment of resources. For example, convection has great implications for aircraft launching from carriers as well as land-based sites.

In order to determine cloud-top heights, knowledge of the cloud top temperature and the temperature structure in the atmosphere is required. Instruments that utilize the infrared (IR) window channel (11.0 um ) only provide estimates of the cloud-top temperatures. On the other hand, data from Rawinsondes, Climatologies and Standard Atmospheres provide the relationships needed to convert such temperatures to heights. However, the major difficulty with the use of these methods arises from the fact that the atmosphere is neither spatially nor temporally constant. Accordingly, errors in excess of 10,000 feet can result. A more accurate means of relating temperature to heights occurs through the use of numerical weather prediction model (NWP) data.

One such method of estimating cloud-top heights currently used at NRL utilizes IR data from geostationary satellites for cloud-top temperatures and standard pressure level air temperatures derived from the Naval Operational Global Atmospheric Prediction System (NOGAPS). The cloud-top temperatures from the IR data are related to model heights by finding the height at which the model derived air temperature matches that of the cloud-top temperature. The resulting heights are real heights above sea level and are then related to the observed Standard Atmosphere altimeter readings used by pilots.

Several examples of the differences between the NRL method and those using Standard Atmospheres highlight the large discrepancies that are possible. The final products produced by NRL methods demonstrate their applicability to tropical weather and their usefulness during Global Hawk flights, Ocean Convection Nowcast Demonstration and Operation Enduring Freedom.

Joint Poster Session 2, Instrumentation and Remote Sensing (Joint with the Symposium on Observing and Understanding the Variability of Water in Weather and Climate and the 17th Conference on Hydrology)
Tuesday, 11 February 2003, 9:45 AM-9:45 AM

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