Day-to-day variability of upper troposphere and lower stratosphere temperature in response to Taal volcanic eruption inferred from COSMIC-2 RO measurements

For the first time after 43 years of its previous eruption in 1977, the Taal volcano in the Philippines (14°N, 120°.59E) erupted in the afternoon of 12 January 2020. Due to the strong anticyclonic circulation in the upper troposphere (~150 hPa), the resultant volcanic ash and sulfur dioxide (SO₂) were transported to the downwind tropical central Pacific Ocean within a few days after the initial eruption. In this study, day-to-day variability of upper troposphere lower stratosphere (UTLS) temperature in response to the Taal volcanic eruption event over the source region (±5^o latitude and longitude around the volcano) and the downwind Pacific region (10-20^oN, 160-180°E) is delineated by using the recently launched Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)-2 radio occultation (RO) data. The daily mean temperature over the source and downwind regions were compared with the background long-term January mean temperature (obtained from 2007 to 2019 COSMIC-1 RO data) over the respective regions. Significant positive temperature anomalies in the lower stratosphere are evident over the source (between 12 and 14 January) and downwind (between 14 and 19 January) regions after the eruption. These positive anomalies may be due to the association of absorption and local radiative heating by volcanic aerosols. The Ozone Monitoring Instrument (OMI) measurements clearly show the presence of SO₂ in the UTLS region. The presence of sulfate aerosols in the UTLS region a few days after eruption is also supported by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) images. Furthermore, we also describe the temperature structure near the volcano and away from the volcano and found a quite different structure in the UTLS region. A significant temperature inversion at ~15 km altitude is evident near the volcano, whereas it is noticed at ~16 km away from the volcano. In conclusion, in line with the previous studies, the present study provides further insights to the UTLS temperature in response to volcanic eruptions.