Barbara Pirscher

Atmospheric temperature change detection with GPS radio occultation 1995 to 2008

[1] Existing upper air records of radiosonde and operational satellite data recently showed a reconciliation of temperature trends but structural uncertainties remain. GPS radio occultation (RO) provides a new high-quality record, profiling the upper troposphere and lower stratosphere with stability and homogeneity. Here we show that climate trends are since recently detected by RO data, consistent with earliest detection times estimated by simulations. Based on a temperature change detection study using the RO record within 1995―2008 we found a significant cooling trend in the tropical lower stratosphere in February while in the upper troposphere an emerging warming trend is obscured by El Nino variability. The observed trends and warming/cooling contrast across the tropopause agree well with radiosonde data and basically with climate model simulations, the latter tentatively showing less contrast. The performance of the short RO record to date underpins its capability to become a climate benchmark record in the future.

Exploration of Climate Data Using Interactive Visualization

In atmospheric and climate research, the increasing amount of data available from climate models and observations provides new challenges for data analysis. The authors present interactive visual exploration as an innovative approach to handle large datasets. Visual exploration does not require any previous knowledge about the data, as is usually the case with classical statistics. It facilitates iterative and interactive browsing of the parameter space to quickly understand the data characteristics, to identify deficiencies, to easily focus on interesting features, and to come up with new hypotheses about the data. These properties extend the common statistical treatment of data, and provide a fundamentally different approach. The authors demonstrate the potential of this technology by exploring atmospheric climate data from different sources including reanalysis datasets, climate models, and radio occultation satellite data. Results are compared to those from classical statistics, revealing the complementary advantages of visual exploration. Combining both the analytical precision of classical statistics and the holistic power of interactive visual exploration, the usual workflow of studying climate data can be enhanced.

New Horizons in Occultation Research

Several GPS Radio Occultation (RO) missions (GRACE-A (GRavity And Climate Experiment), FORMOSAT-3/COSMIC (FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate), and MetOp) started data provision in 2006 and 2007. Together with the measurements from CHAMP (CHAllenging Minisatellite Payload, since 2001) and the recently launched (June 15, 2007) TerraSAR-X an operational multi-satellite constellation for precise GPS based atmospheric sounding became reality. The data base is supplemented by measurements from SAC-C (Satelite de Aplicaciones Cientificas-C). Our contribution briefly reviews current GFZ activities regarding processing and application of GPS RO data from different satellites. These activities include precise satellite orbit determination and the provision of near-real time analysis results for weather forecast centers within 2 h after measurement. Available satellite data are used for climatological investigations of global gravity wave characteristics.

Climatologies Based on Radio Occultation Data from CHAMP and Formosat-3/COSMIC

Radio Occultation (RO) data using Global Navigation Satellite System (GNSS) signals have the potential to deliver climate benchmark measurements, since they can be traced, at least in principle, to the international standard for the second. The special climate utility of RO data arises from their accuracy and long-term stability due to self-calibration. The German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) provided the first opportunity to create RO based climatologies over more than 6 years. Overlap with data from the Taiwan/US Formosat-3/COSMIC (Formosa Satellite Mission 3/Constellation Observing System for Meteorology, Ionosphere, and Climate, F3C) mission allows testing the consistency of climatologies derived from different satellites. We show results for altitude- and latitude-resolved seasonal zonal mean dry temperature climatologies. Our results indicate excellent agreement between RO climatologies from different F3C satellites: After subtraction of the estimated respective sampling errors, differences are smaller than 0.1 K almost everywhere in the considered domain between 8 km and 35 km altitude. Mean differences (over the same domain) are smaller than 0.03 K in any case and can be as small as 0.003 K. Differences between F3C and CHAMP are only slightly larger. The assimilation of RO data at ECMWF (European Centre for Medium-Range Weather Forecasts) considerably improved operational analyses in regions where the data coverage and/or the vertical resolution and accuracy of RO data is superior to traditional data sources.

Correction to “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008”

Citation: Steiner, A. K., G. Kirchengast, B. C. Lackner, B. Pirscher, M. Borsche, and U. Foelsche (2010), Correction to “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008,” Geophys. Res. Lett., 37, L03704, doi:10.1029/2010GL042427. [1] In the paper “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008” by A. K. Steiner et al. (Geophys. Res. Lett., 36, L18702, doi:10.1029/2009GL039777), Figure S7 of the auxiliary material is incorrect and the corrected version appears here.

The GPS radio occultation record – a novel dataset for atmospheric change detection

Fig. 1: Radio signals from a GPS satellite are received onboard a LEO satellite such as CHAMP. An occultation occurs whenever a GPS satellite sets (or rises from) behind the horizon and is occulted by the Earth’s limb as viewed from the receiver. The relative movement of the satellites provides a scan through the atmosphere. Inserts illustrate a retrieved RO CHAMP temperature profile for a particular RO event (A), a distribution of RO events in February 2004 (B), and a monthly mean temperature field for February 2004 (C). TRANSMITTER A