Andrea K. Steiner

Prospects of the EPS GRAS Mission For Operational Atmospheric Applications

Abstract Global Navigation Satellite System (GNSS) Receiver for Atmospheric Sounding (GRAS) is a radio occultation instrument especially designed and built for operational meteorological missions. GRAS has been developed by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) in the framework of the EUMETSAT Polar System (EPS). The GRAS instrument is already flying on board the first MetOp satellite (MetOp-A) that was launched in October 2006. It will also be on board two other MetOp satellites (MetOp-B and MetOp-C) that will successively cover the total EPS mission lifetime of over 14 yr. GRAS provides daily about 600 globally distributed occultation measurements and the GRAS data products are disseminated to the users in near–real time (NRT) so that they can be assimilated into numerical weather prediction (NWP) systems. All GRAS data and products are permanently archived and made available to the users for climate applications and sc...

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.

GNSS Occultation Sounding for Climate Monitoring

Considerable efforts are currently invested into the setup of a Global Climate Observing System (GCOS) for monitoring climate change over the coming decades, which is of high relevance given concerns on increasing human influences. A promising potential contribution to the GCOS is a suite of spaceborne Global Navigation Satellite System (GNSS) occultation sensors for global long-term monitoring of atmospheric change in temperature and other variables with high vertical resolution and accuracy. Besides the great importance with respect to climate change, the provision of high quality data is essential for the improvement of numerical weather prediction and for reanalysis efforts. We review the significance of GNSS radio occultation sounding in the climate observations context. In order to investigate the climate change detection capability of GNSS occultation sensors, we are currently performing an end-to-end GNS

Hypothesis Generation in Climate Research with Interactive Visual Data Exploration

occultation observing system simulation experiment over the 25-year period 2001 to 2025. We report on this integrated analysis, which involves in a realistic manner all aspects from modeling the atmosphere via generating a significant set of simulated measurements to an objective statistical analysis and assessment of 2001-2025 temporal trends. Q 200 1 Elsevier

Gravity Wave Spectra from GPS/MET Occultation Observations

One of the most prominent topics in climate research is the investigation, detection, and allocation of climate change. In this paper, we aim at identifying regions in the atmosphere (e.g., certain height layers) which can act as sensitive and robust indicators for climate change. We demonstrate how interactive visual data exploration of large amounts of multi-variate and time-dependent climate data enables the steered generation of promising hypotheses for subsequent statistical evaluation. The use of new visualization and interaction technology-in the context of a coordinated multiple views framework-allows not only to identify these promising hypotheses, but also to efficiently narrow down parameters that are required in the process of computational data analysis. Two datasets, namely an ECHAM5 climate model run and the ERA-40 reanalysis incorporating observational data, are investigated. Higher-order information such as linear trends or signal-to-noise ratio is derived and interactively explored in order to detect and explore those regions which react most sensitively to climate change. As one conclusion from this study, we identify an excellent potential for usefully generalizing our approach to other, similar application cases, as well.

Occultations for Probing Atmosphere and Climate

Abstract The potential utility of radio occultation data in general, and of data from the Global Positioning System/Meteorology (GPS/MET) experiment in particular, for studying atmospheric gravity waves is discussed. Based on a validated set of ∼270 GPS/MET-derived temperature profiles, the authors produced and analyzed mean vertical wavenumber power spectra of normalized temperature fluctuations in three latitude bands (low, middle, high) within the lower stratosphere (∼15–30 km), where data accuracy was proven highest. The Fresnel diffraction limited vertical resolution and the limited height range of the dataset restricted this initial investigation to medium- to large-scale waves with vertical wavelengths of about 2–5 km. The deduced vertical wavenumber power spectra were compared with a saturation spectrum predicted by gravity wave saturation theory and generally found consistent with the theoretical saturation limit. The low-latitude power spectra exhibited almost saturation, with spectral power abo...

Exploration of Climate Data Using Interactive Visualization

Occultations for Probing Atmosphere and Climate: Setting the Scene.- 1. Occultation Methodology in General.- Wave Optics Algorithms for Processing Radio Occultation Data in the Lower Troposphere: A Review and Synthesis.- The Radio-Holography Approach for GNSS Occultation Data Analysis: Review and Application to Resolving Fine Structures in the Atmosphere and Mesosphere.- Open Loop Tracking and Inverting GPS Radio Occultation Signals: Simulation Study.- Fourier Analysis of GNSS-LEO Radio Occultation Signals, Resolution and Limitations.- Canonical Transform Methods for Radio Occultation Data.- Unfolding of Radio Occultation Multipath Behavior Using Phase Models.- Abel Integral Inversion in Occultation Measurements.- Does a Priori Information Improve Occultation Measurements?.- Retrieval of Atmospheric Refractivity Profiles from Ground-Based GPS Measurements.- 2. GNSS-LEO Occultation.- GRAS-SAF Radio Occultation Data from EPS/Metop.- Deviations from a Hydrostatic Atmosphere in Radio Occultation Data.- Sensitivity of GNSS Occultation Profiles to Horizontal Variability in the Troposphere: A Simulation Study.- Advancement of GNSS Radio Occultation Retrieval in the Upper Stratosphere.- Ensemble-Based Analysis of Errors in Atmospheric Profiles Retrieved from GNSS Occultation Data.- Refractivity Profiles Obtained by Abel Inversion from a Down Looking GPS Radio Occultation Experiment at Mt. Fuji: Preliminary Results and Future Plan.- 3. LEO-LEO Occultation.- An Active Microwave Limb Sounder for Profiling Water Vapor, Ozone, Temperature, Geopotential, Clouds, Isotopes and Stratospheric Winds.- An Overview of the University of Arizona ATOMS Project.- The ACE+ Mission: An Atmosphere and Climate Explorer Based on GPS, GALILEO, and LEO-LEO Radio Occultation.- Simulating the Influence of Horizontal Gradients on Retrieved Profiles from ATOMS Occultation Measurements - A Promising Approach for Data Assimilation.- Water Vapor Profiling Using Absorptive Occultation Measurements: A Comparison Between SAGE III and ATOMS.- The Genesis of the ACE+ Anti-Rotating Satellites Concept.- 4. Stellar and Solar Occultation.- The Stellar Occultation Technique: Past Achievements, Recent Developments, and Future Challenges.- Envisat/GOMOS Stellar Occultation: Inversion Schemes and First Analyses of Real Data.- Atmospheric Density, Pressure and Temperature Profile Reconstruction from Refractive Angle Measurements in Stellar Occultation.- Stratospheric Temperature and Ozone Sounding with ENVISAT/GOMOS Stellar Occultation.- Information Approach to Channel Selection for Stellar Occultation Measurements.- The Solar Occultation Mission ACE: An Overview.- Mesospheric Temperature and Ozone Sounding by the SMAS Solar Occultation Sensor.- 5. Use of Occultation Data.- Utility of Occultations for Atmospheric Wave Activity Studies: Results of GPS/MET Data Analyses and Future Plan.- Stratospheric Gravity Wave Fluctuations and Sporadic E at Mid-Latitudes with Focus on Possible Effects of the Andes.- The Detection of Upper Level Turbulence via GPS Occultation Methods.- Evaluation of Refractivity Profiles from CHAMP and SAC-C GPS Radio Occultation.- Ionospheric Radio Occultation Measurements and Space Weather.- The Mars Atmospheric Constellation Observatory (MACO) Concept.- Author Index.

Pre-Operational Retrieval of Radio Occultation Based Climatologies

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.

The CHAMPCLIM Project: An Overview

CHAMPCLIM is a joint project of WegCenter/UniGraz and GFZ Potsdam. The overall aim of the project is to exploit the CHAMP (CHAllenging Minisatellite Payload for geoscientific research) radio occultation (RO) data in the best possible manner for climate monitoring. This paper focuses on describing the pre-operational status and technical aspects of the CHAMPCLIM processing system at WegCenter/UniGraz. For creating RO based climatologies we ingest, on the one hand, the complete CHAMP RO dataset provided by GFZ at excess phase level (GFZ level 2, ∼180 profiles/day), which is processed to obtain atmospheric profiles of refractivity, geopotential height, and temperature (in future also humidity). On the other hand, we use operational atmospheric analysis fields from the European Centre for Medium-Range Weather Forecasts (ECMWF), at T42L60 resolution, as reference for quality control and evaluation. For delivering climatologies operationally, which will be prepared at monthly, seasonal, and annual time scales, our aim is to provide them with a delay of at most two weeks after the last measurement (e.g., JJA 2003 seasonal climatology available by September 14, 2003, latest). The climatologies are set up in overlapping equal-area and non-overlapping almost equal-area grids. In order to monitor the error characteristics of the climatologies, various types of error statistics (vs. ECMWF analyses) are performed. The main emphasis of this paper lies on processing the complete 2002–2004 data — starting from March 2002 when the CHAMP data stream became stable and quasi continuous — and on creation of climatologies including error estimates. The spatial set up of the climatologies, exemplary seasonal climatologies (as far as processed) as well as preliminary climatological error estimates are presented.

Connecting Atmospheric Blocking to European Temperature Extremes in Spring

The CHAMP radio occultation (RO) data provide the first opportunity to create real RO based climatologies on a longer term. CHAMPCLIM is a joint project of the Institute for Geophysics, Astrophysics, and Meteorology (IGAM) in Graz and the GeoForschungsZentrum (GFZ) in Potsdam. The overall aim of CHAMPCLIM is to ensure that the CHAMP RO data are exploited in the best possible manner, in particular for climate monitoring. The main objectives of the CHAMPCLIM project can be summarized in form of three areas of study as follows: RO data processing advancements for optimizing climate utility, RO data and algorithms validation based on CHAMP/GPS data, and global RO based climatologies for monitoring climate change. Here we show a summary of the current activities and exemplary results.