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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 1093-1110, 2017
https://doi.org/10.5194/amt-10-1093-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Mar 2017
Tropospheric dry layers in the tropical western Pacific: comparisons of GPS radio occultation with multiple data sets
Therese Rieckh1,2, Richard Anthes1, William Randel3, Shu-Peng Ho1, and Ulrich Foelsche4,2 1COSMIC Program Office, University Corporation for Atmospheric Research, Boulder, Colorado, USA
2Wegener Center for Climate and Global Change, University of Graz, Graz, Austria
3National Center for Atmospheric Research, Boulder, Colorado, USA
4Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Austria
Abstract. We use GPS radio occultation (RO) data to investigate the structure and temporal behavior of extremely dry, high-ozone tropospheric air in the tropical western Pacific during the 6-week period of the CONTRAST (CONvective TRansport of Active Species in the Tropics) experiment (January and February 2014). Our analyses are aimed at testing whether the RO method is capable of detecting these extremely dry layers and evaluating comparisons with in situ measurements, satellite observations, and model analyses. We use multiple data sources as comparisons, including CONTRAST research aircraft profiles, radiosonde profiles, AIRS (Atmospheric Infrared Sounder) satellite retrievals, and profiles extracted from the ERA (ERA-Interim reanalysis) and the GFS (US National Weather Service Global Forecast System) analyses, as well as MTSAT-2 satellite images. The independent and complementary radiosonde, aircraft, and RO data provide high vertical resolution observations of the dry layers. However, they all have limitations. The coverage of the radiosonde data is limited by having only a single station in this oceanic region; the aircraft data are limited in their temporal and spatial coverage; and the RO data are limited in their number and horizontal resolution over this period. However, nearby observations from the three types of data are highly consistent with each other and with the lower-vertical-resolution AIRS profiles. They are also consistent with the ERA and GFS data. We show that the RO data, used here for the first time to study this phenomenon, contribute significant information on the water vapor content and are capable of detecting layers in the tropics and subtropics with extremely low humidity (less than 10 %), independent of the retrieval used to extract moisture information. Our results also verify the quality of the ERA and GFS data sets, giving confidence to the reanalyses and their use in diagnosing the full four-dimensional structure of the dry layers.

Citation: Rieckh, T., Anthes, R., Randel, W., Ho, S.-P., and Foelsche, U.: Tropospheric dry layers in the tropical western Pacific: comparisons of GPS radio occultation with multiple data sets, Atmos. Meas. Tech., 10, 1093-1110, https://doi.org/10.5194/amt-10-1093-2017, 2017.
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Short summary
We use GPS radio occultation (RO) data to investigate the structure and temporal behavior of extremely dry, high-ozone tropospheric air in the tropical western Pacific and compare them to various data sets (research aircraft, radiosonde, infrared sounder, and model reanalyses). All these data sets have limitations. We show that the RO data contribute significant information on the water vapor content. Our results also verify the quality of the reanalyses.
We use GPS radio occultation (RO) data to investigate the structure and temporal behavior of...
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