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| Titel |
Upper Tropospheric and Lower Stratospheric Diurnal Tides of Temperature Derived from Radio Occultation Measurements |
| VerfasserIn |
B. Pirscher, U. Foelsche, M. Borsche, G. Kirchengast, Y.-H. Kuo |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030559
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| Zusammenfassung |
| We investigate the diurnal tide of temperature derived from Global Positioning
System (GPS) radio occultation (RO) data of the Formosat-3/COSMIC (Constellation
Observing System for Meteorology Ionosphere and Climate) satellite constellation. The
constellation consists of six satellites, which were launched in April 2006. Since
mid-2007 local time coverage is sufficient to allow the observation of the diurnal tide
typical for one month at almost all latitudes. Only at high latitudes (beyond 70-),
where ascending and descending branch of the satellite orbit move together (in
terms of local time), local time sampling is insufficient and irregular within one
month.
We use retrieved dry temperature profiles of Formosat-3/COSMIC RO measurements
provided by UCAR/CDAAC (University Corporation for Atmospheric Research/COSMIC
Data Analysis and Archive Center). We estimate the diurnal tide of temperature in 5- zonal
bands between an altitude of 4Â km and 35Â km on a monthly scale. We compare the diurnal
tides for northern hemispheric summer months June, July, and August 2007 and 2008 and
show also results from the northern hemispheric winter months December, January, and
February 2007/08.
At low latitudes, where seasonal variability is negligible, we find a downward propagating
phase in all months. It is most pronounced between 15-N and 15-S and may be attributed to
an upward propagating diurnal tide. Amplitude and phase observations are in excellent
agreement with the tropical diurnal tide determined from ECMWF (European Centre for
Medium-Range Weather Forecasts) short-term forecast fields (24Â h to 48Â h forecasts,
temporal resolution of 3Â hours).
Comparing the diurnal tides from ECMWF forecasts and Formosat-3/COSMIC
measurements at latitudes beyond 20-, similarities become smaller and turn into disparities.
On the one hand, the diurnal tide of the ECMWF model is very weakly pronounced and
maximum temperatures are always observed in the afternoon. Formosat-3/COSMIC data, on
the other hand, show a more strongly pronounced diurnal tide at mid- and high latitudes and
the local time of maximum temperatures varies with latitude, height, and season. The
measurement results are consistent between the northern hemispheric summer months of
2007 and 2008.
We also discuss results of space-time spectral analysis performed to specify the
characteristics of the diurnal tides—the zonal wavenumbers, the directions (east or west), and
the periods of the waves. |
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