Long-term evolution of stratospheric water vapour using TIMED/ SABER measurements

One of the most prevalent greenhouse gases in the atmosphere is water vapour, which exhibits significant variability both in space and time. The water vapour warms the troposphere whereas it cools the stratosphere through radiative cooling and thus regulates the thermal structure of the stratosphere impacting the stratosphere-troposphere coupling process. The ground based measurements of stratospheric water vapour (SWV) are limited across the globe and the space based observations provide global distribution, which is very important for accessing it role in climate. The present study focuses on investigating the long-term evolution of SWV using Sounding Atmospheric Broadband Emission Radiometry (SABER) measurements onboard Thermosphere-Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to December 2023. The results show that SWV magnitudes are extremely low in the lower stratosphere (3–5 ppmv) and relative high in the upper stratosphere (7–8 ppmv) owing to the methane oxidation in the upper stratosphere. The lower stratosphere exhibits relatively high variability as compared to upper stratosphere. The time series of water vapour shows robust increasing trend throughout the stratosphere. The analysis carried out separately for the period 2002–2012 and 2013–2023 show that the water vapour distribution peaks around 4.8 ppmv during 2002 to 2012 and around 5.0 ppmv during 2013 to 2023 at 30 km altitude. The frequency of distribution of SWV clearly shows a shift towards higher concentration. The long-term evolution of SWV shows an increasing trend in the entire stratosphere with a peak of 0.8ppmv/decade at 22 km altitude over the tropics. The analysis also has shown that the tropical latitude exhibits relatively large increasing trends as compared to global mean thus emphasizing the importance of focusing on tropical processes responsible for observed SWV enhancement and their impact on climate.