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  1. null (Ed.)
  2. Abstract

    The satellite‐based Cloud Imaging and Particle Size (CIPS) instrument and Atmospheric Infrared Sounder (AIRS) observed concentric gravity waves (GWs) generated by Typhoon Yutu in late October 2018. This work compares CIPS and AIRS nadir viewing observations of GWs at altitudes of 50–55 and 30–40 km, respectively, to simulations from the high‐resolution European Centre for Medium‐Range Weather Forecasting Integrated Forecasting System (ECMWF‐IFS) and ECMWF reanalysis v5 (ERA5). Both ECMWF‐IFS with 9 km and ERA5 with 31 km horizontal resolution show concentric GWs at similar locations and timing as the AIRS and CIPS observations. The GW wavelengths are ∼225–236 km in ECMWF‐IFS simulations, which compares well with the wavelength inferred from the observations. After validation of ECMWF GWs, five category five typhoon events during 2018 are analyzed using ECMWF to obtain characteristics of concentric GWs in the Western Pacific regions. The amplitudes of GWs in the stratosphere are not strongly correlated with the strength of typhoons, but are controlled by background wind conditions. Our results confirm that amplitudes and shapes of concentric GWs observed in the stratosphere and lowermost mesosphere are heavily influenced by the background wind conditions.

     
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  3. Abstract

    It is well known that stratospheric sudden warmings (SSWs) are a result of the interaction between planetary waves (PWs) and the stratospheric polar vortex. SSWs occur when breaking PWs slow down or even reverse this zonal wind jet and induce a sinking motion that adiabatically warms the stratosphere and lowers the stratopause. In this paper we characterize this downward progression of stratospheric temperature anomalies using 18 years (2003–2020) of Sounding of the Atmosphere using Broadband Radiometry (SABER) observations. SABER temperatures, derived zonal winds, PW activity and gravity wave (GW) activity during January and February of each year indicate a high‐degree of year‐to‐year variability. From 11 stratospheric warming events (9 major and 2 minor events), the descent rate of the stratopause altitude varies from 0.5 to 2 km/day and the lowest altitude the stratopause descends to varies from <20 to ∼50 km (i.e., no descent). A composite analysis of temperature and squared GW amplitude anomalies indicate that the downward descent of temperature anomalies from 50 to ∼25 km lags the downward progression of increased GW activity. This increased GW activity coincides with the weakening and reversal of the westward zonal winds in agreement with previous studies. Our study suggests that although PWs drive the onset of SSWs at 30 km, GWs also play a role in contributing to the descent of temperature anomalies from the stratopause to the middle and lower stratosphere.

     
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