Using GNSS Radio Occultation Data to Monitor Tropical Atmospheric Anomalies during the January-February 2009 Sudden Stratospheric Warming Event

We used Global Navigation Satellite System (GNSS) radio occultation (RO) temperature, density, and bending angle profiles to monitor tropical atmospheric anomalies during the January-February 2009 sudden stratospheric warming (SSW) event on a daily basis. We constructed RO anomaly profiles (tropical mean (30 degrees S-30 degrees N)) and gridded mean anomalies, as well as tropopause height and temperature anomalies. Based on the anomalies, we investigated the response time and region of the tropical atmosphere to SSW. It was found that the GNSS RO data were robust in monitoring tropical atmospheric anomalies during SSW. The tropical stratosphere revealed cooling simultaneously with polar stratospheric warming, although the magnitudes of the maximum tropical mean anomalies were 6-7 times smaller than the polar mean. Altitude variations showed that tropical stratospheric anomalies were largest within 35-40 km, which were 5 km higher than those in the polar region. On the onset day of 23 January, temperature anomalies over 0-30 degrees N were mostly more than -5 K, which were larger than those of -2 K detected over the 0-30 degrees S band, and the largest anomalies were detected over northern Africa with values more than -10 K. RO density and bending angle anomalies responded to SSW in a similar way as temperature but were 20 km higher. Following cooling, the tropical upper stratosphere and lower mesosphere revealed visible warming, with anomalies more than 10 K in the sector of 15 degrees S-15 degrees N. Tropopause anomalies revealed the largest variations over 20 degrees N-30 degrees N, further confirming that the extratropical region of the northern hemisphere is a key region for the dynamical coupling between the polar and tropical regions. Tropopause height anomalies had clear increase trends from 16 January to 8 February, with anomalies of the 20 degrees N-30 degrees N band that were -2 km on Jan 16 and increased to -0.5 km on Feb 6 with a variation of 1.5 km, while variations in other bands were within 0.5 km. Tropopause temperature anomalies had clear decrease trends over the same period, with anomalies at 20 degrees N-30 degrees N of 4 K on 16 January and decreasing to about -1 K on 8 February, while anomalies in other bands showed variations within 3 K.