GPS radio occultation data from the CDAAC: COSMIC Data Analysis and Archive Centre

The GPS RO technique has a number of advantages over the traditional RS such as its global coverage, high vertical resolution, 24 hour availability, high accuracy, all weather capability and lack of bias effects. The RO data contains high resolution height, temperature, pressure, refractivity, bending angle and water vapour content at the tangent point locations. There are a number of satellite constellations that are capable of deriving RO measurements. In this project we utilised data from the FORMOSAT-3 (Taiwan's Formosa Satellite Missions # 3)/ COSMIC (Constellation Observing System for Meteorology Ionosphere and Climate) and CHAMP (CHAllenging Minisatellite Payload) satellites. These constellations are capable of producing many measurements daily, the Cosmic Data Analysis and Archive Centre (CDAAC) provides around 1800 neutral atmospheric profiles per day.

RS measurements have been the dominant method for the acquisition of upper air atmospheric information for the last 70 years. The RS monitoring technique measures atmospheric profiles of pressure, temperature and humidity using sensors attached to balloons. The data collected by the sensors is transmitted to the ground based weather station. The usual operational frequency is two times per day (0000 and 1200 UT). A global RS network of approximately 1500 stations is currently in operation. The RS monitoring method has a limited coverage, low spatial and temporal resolution and is normally restricted to land masses.

In the Antarctic region there are only 16 weather stations mainly distributed along the coastal fringe due to the environmental harshness and costs involved. As such this RS network is far from ideal for studying the atmosphere, meteorology and climatology in the Antarctic region. It does however provide excellent reference stations to test and validate the RO technique as a suitable meteorological data type in the Antarctic region.

These data were downloaded from the CDAAC: COSMIC Data Analysis and Archive Centre website.
http://cdaac-www.cosmic.ucar.edu/cdaac/index.html

These data are freely available.

We downloaded and used data from the CHAMP and COSMIC wetPrf, atmPrf and sonPrf data files.

The GPS RO data was tested against co-located radiosonde measurements from 16 radiosonde weather stations located in Antarctica. We investigated the spatial and temporal buffer required for a large and accurate data set. We found that a spatial and temporal buffer set of 300km and 3 hours to be appropriate to test the RO data sets. The RO data sets were found to match well with the radiosonde measurements in the Antarctic region.

We then used these data sets to investigate annual, bimonthly temperature trends at various heights (pressure levels) and at various locations.

These data were collected by the CDAAC: COSMIC Data Analysis and Archive Centre.
We used COSMIC data collected from 1st January 2007 to 31st December 2014.
We used CHAMP data collected from 2003 to 2008.