Observations and trends of clouds based on GOES sounder data

Abstract

Abstract. A 26 month (November 1997 through December 1999) data set of Geostationary Operational Environmental Satellite (GOES) sounder-derived cloud parameters has been analyzed to discern annual and monthly trends. An important outcome of this study is the identification of diurnal trends made possible by the geostationary satellite frequent observations over specific locations. The area of coverage is 20øN to 50øN and 60øW to 160øW, which corresponds to the continental United States and the surrounding waters. The satellite cloud observations were compared to manually observed Pilot Reports (PIREPs) and were found to be, on average, 35 hPa lower. Comparing the frequency of GOES sounder observations of high cloudiness with observations from the National Oceanic and Atmospheric Administration (NOAA) series of polar orbiting weather satellites reveals a correlation coefficient of 0.79 and a bias of 3.4% for the frequency of occurrence (GOES with a mean higher height). The frequency of occurrence and distribution of clouds, cloud top pressure (CTOP), and effective cloud amount are based on a spatial resolution of -40 km (3 x 3 field of view box) and are shown for eight regions. High clouds (CTOP -<300 hPa) are found to be more prevalent during the Northern Hemisphere summer than winter for all regions. High clouds for 1998 comprise 8.5% of all observations. Also, in 1998 clear conditions are observed -34% of the time. Focusing on the strength of the hourly GOES sounder data, it is found that thin high clouds are most prevalent during the summer and fall seasons, occurring most frequently in the late morning and early afternoon. IntroductionThe current series of the Geostationary Operational Environmental Satellite (GOES) carry a sounder that observes 1 visible and 18 infrared channels and an imager that observes 1 visible and 4 infrared channels. The strength of a geostationary satellite is its ability to provide frequent observations over a specific location. Therefore an important outcome of this study is the characterization of diurnal trends. A region over the central United States is examined for diurnal fluctuations in cloud cover using the GOES sounder data.This paper also provides background on the sounder-derived cloud product by describing the techniques for determining cloudy fields of view (FOV) and how the cloud parameters are generated along with a description of the data set (section 2). Section 3 provides comparisons of the remotely sensed parameters to PIREPs of cloud top pressure. Sections 4 through 6 focus on annual distributions, monthly variations, and diurnal characteristics of the remotely sensed clouds, respectively. The results and future work are summarized in section 7. Background Detection of Cloud in a Field of ViewDetermining whether a FOV (the area over which the instrument takes instantaneous data) is clear or cloudy is a challenging task. A detailed explanation can be found in Appendix A. A short overview is presented here.The infrared bands (wavelengths) used from the GOES sound...

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