New Horizons in Occultation Research Studies in Atmosphere and Clima
This book presents carefully edited and peer-reviewed papers from the 3rd International Workshop on Occultations for Probing Atmosphere and Climate (OPAC-3), held in Graz, Austria. Starting with an overview on occultation methodology and its applications,
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Abstact The Formosat-3/COSMIC satellite constellation, performing radio occultation measurements, allows for an adequate measurement density in space and time to determine the temperature diurnal tide typical for one month, i.e., on a monthly basis. In this initial study on the topic we investigated the diurnal amplitude and phase between 4 km and 35 km altitude in different geographical regions in July 2007. The tropical diurnal tide shows a distinctive downward phase progression. The corresponding amplitude is increasing towards higher altitudes but it always remains smaller than 0.5 K up to an altitude of 35 km. Natural temperature variability within large latitudinal domains seems to interfere with the diurnal tide, which complicates the interpretation of our extratropical results. We found maximum temperature amplitude within a day in the afternoon at high latitudes with an increase in amplitude with altitude. The tide is more pronounced in the winter hemisphere.
1 Introduction Nearly continuous measurements at synoptic land stations, ships, and buoys allow an adequate determination of the diurnal tide of atmospheric parameters, e.g., temperature or humidity, at the surface. Some of these data are available since the end of the 19th century. From 1950 until 2004 a decrease in the diurnal surface temperature range occurred due to a steeper increase in daily minimum surface temperatures than in daily maximum surface temperatures (Vose et al. 2005; Easterling et al. 2006). Since 1979, however, no change in temperature range is observed (Trenberth et al. 2007). The number of measurements and the spatial density in the upper troposphere and lower stratosphere (UTLS) region was very sparse in the pre-satellite era (before B. Pirscher (B) Wegener Center for Climate and Global Change (WegCenter) and Institute for Geophysics, Astrophysics, and Meteorology (IGAM), University of Graz, Austria e-mail: [email protected] A. Steiner et al. (eds.), New Horizons in Occultation Research, C Springer-Verlag Berlin Heidelberg 2009 DOI 10.1007/978-3-642-00321-9 11,
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1979), since radiosonde, lidar, and radar data were the only measurements available in the free atmosphere. To estimate the diurnal tide in the free atmosphere it is necessary to analyze data from radiosonde measurement campaigns with at least four radiosonde ascends per day (e.g., Seidel et al. 2005; Alexander and Tsuda 2008), to examine lidar/radar data (e.g., Revathy et al. 2001; Riggin et al. 2002) or to investigate satellite data (e.g., Zeng et al. 2008). The lack of long term measurements in the UTLS region prevents the examination of a possible climate change impact on the diurnal tide in the free atmosphere. In the recent past, discussion about temperature trends in the free atmosphere derived from (Advanced) Microwave Sounding Unit (MSU/AMSU) satellite data received much attention. Discrepancies in sign and magnitude of the trends arose from incorrect inter-calibration and correction procedures between the different
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