Abstract
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.
Highlights
Water vapor is the most important greenhouse gas in the troposphere, yet it is still the parameter with the highest uncertainty in weather and climate models
The radio occultation (RO) method does not suffer from these limitations, but water vapor information can only be derived by using a combination of RO data and information on temperature from another source
We found that many CONTRAST vs. RO profile pairs matched very closely, but some of the pairs showed relative humidity (RH) differences of more than 60 % at certain levels
Summary
Water vapor is the most important greenhouse gas in the troposphere, yet it is still the parameter with the highest uncertainty in weather and climate models. Cau et al (2005) investigated the radiative impact and origin of dry intrusions observed by RS profiles in the tropical western Pacific using 40-year European Centre for MediumRange Weather Forecasts (ECMWF) reanalysis (ERA-40) wind and humidity data They showed an outgoing longwave radiation increase of 3 W m−2 per 100 hPa for dry intrusions with relative humidities of less than 20 %, almost independent of altitude. Casey et al (2009) created a 5-year climatology on dry layers between 600 and 400 hPa over deep convective regions of the tropical oceans using AIRS (Atmospheric Infrared Sounder) data Their results show large spatial and seasonal variability for different ocean basins, pointing out the limits of applying case study trends to the whole basin.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
