A New Method for Detecting and Monitoring Atmospheric Natural Hazards with GPS RO

Abstract:

Global Positioning System (GPS) Radio Occultation (RO) allows measurements in any meteorological condition, with global coverage, high vertical resolution, and high accuracy. With more than 13 years of data availability, RO also became a fundamental tool for studying climate change. We present here the application of RO for detecting and monitoring tropical cyclones (TCs), deep convective systems (CSs) and volcanic ash clouds (ACs).Deep CSs and TCs play a fundamental role in atmospheric circulation producing vertical transport, redistributing water vapor and trace gases, changing the thermal structure of the Upper Troposphere and Lower Stratosphere (UTLS) and affecting climate through overshooting into the stratosphere. Explosive volcanic eruptions produce large ACs dangerous for the aviation and they can impact climate when the ash is injected into the UTLS.

The detection of cloud top height, the determination of cloud extent, the discrimination of ACs from CSs clouds and the detection of overshooting are main challenges for atmospheric natural hazards study. We created a reference atmosphere with a resolution of 5° in latitude and longitude, sampled on a 1° x 1° grid, and a vertical sampling of 100 m. We then compared RO profiles acquired during TCs, CSs and ACs to the reference atmosphere and computed anomaly profiles.CSs, TCs and the ACs leave a clear signature in the atmosphere which can be detected by RO. Using RO temperature and bending angle profiles we gain insight into the vertical thermal structure and developed a new method for detecting the cloud top altitude with high accuracy.

We have characterized the TCs by ocean basins and intensities, showing that they have a different thermal structure and reach to different altitudes according to the basin. We provide statistics on overshooting frequency, achieving results consistent with patterns found in the literature and demonstrating that RO is well suited for this kind of study.

We have analyzed the Nabro 2010 eruption determining the AC top height and analyzing the long term impact of the eruption in the zonal UTLS thermal structure. The results show that there is a signature allowing the discrimination of ACs from CSs clouds. The comparison of AC top height with the tropopause altitude shows that during Nabro eruption the ash reached the UTLS.