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| Titel |
Advances and limitations of atmospheric boundary layer observations with GPS occultation over southeast Pacific Ocean |
| VerfasserIn |
F. Xie, D. L. Wu, C. O. Ao, A. J. Mannucci, E. R. Kursinski |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 2 ; Nr. 12, no. 2 (2012-01-19), S.903-918 |
| Datensatznummer |
250010538
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| Publikation (Nr.) |
 copernicus.org/acp-12-903-2012.pdf |
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| Zusammenfassung |
| The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific
Ocean is featured with a strong temperature inversion and a sharp moisture
gradient across the ABL top. The strong moisture and temperature gradients
result in a sharp refractivity gradient that can be precisely detected by
the Global Positioning System (GPS) radio occultation (RO) measurements. In
this paper, the Constellation Observing System for Meteorology, Ionosphere
& Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution
ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect
a wide range of ABL height variations (1–2 km) as observed from the
radiosondes. However, the ECMWF analysis systematically underestimates the
ABL heights. The sharp refractivity gradient at the ABL top frequently
exceeds the critical refraction (e.g., −157 N-unit km−1) and becomes
the so-called ducting condition, which results in a systematic RO
refractivity bias (or called N-bias) inside the ABL. Simulation study based
on radiosonde profiles reveals the magnitudes of the N-biases are vertical
resolution dependent. The $N$-bias is also the primary cause of the
systematically smaller refractivity gradient (rarely exceeding −110 N-unit km−1)
at the ABL top from RO measurement. However, the N-bias seems not
affect the ABL height detection. Instead, the very large RO bending angle
and the sharp refractivity gradient due to ducting allow reliable detection
of the ABL height from GPS RO. The seasonal mean climatology of ABL heights
derived from a nine-month composite of COSMIC RO soundings over the SE
Pacific reveals significant differences from the ECMWF analysis. Both show
an increase of ABL height from the shallow stratocumulus near the coast to a
much higher trade wind inversion further off the coast. However, COSMIC RO
shows an overall deeper ABL and reveals different locations of the minimum
and maximum ABL heights as compared to the ECMWF analysis. At low latitudes,
despite the decreasing number of COSMIC RO soundings and the lower
percentage of soundings that penetrate into the lowest 500-m above the
mean-sea-level, there are small sampling errors in the mean ABL height
climatology. The difference of ABL height climatology between COSMIC RO and
ECMWF analysis over SE Pacific is significant and requires further studies. |
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