Temperature trends in the tropical upper troposphere and lower stratosphere: Connections with sea surface temperatures and implications for water vapor and ozone

Abstract

[1] Satellite observations and chemistry-climate model experiments are used to understand the zonal structure of tropical lower stratospheric temperature, water vapor, and ozone trends. The warming in the tropical upper troposphere over the past 30 years is strongest near the Indo-Pacific warm pool, while the warming trend in the western and central Pacific is much weaker. In the lower stratosphere, these trends are reversed: the historical cooling trend is strongest over the Indo-Pacific warm pool and is weakest in the western and central Pacific. These zonal variations are stronger than the zonal-mean response in boreal winter. Targeted experiments with a chemistry-climate model are used to demonstrate that sea surface temperature (hereafter SST) trends are driving the zonal asymmetry in upper tropospheric and lower stratospheric tropical temperature trends. Warming SSTs in the Indian Ocean and in the warm pool region have led to enhanced moist heating in the upper troposphere, and in turn to a Gill-like response that extends into the lower stratosphere. The anomalous circulation has led to zonal structure in the ozone and water vapor trends near the tropopause, and subsequently to less water vapor entering the stratosphere. The radiative impact of these changes in trace gases is smaller than the direct impact of the moist heating. Projected future SSTs appear to drive a temperature and water vapor response whose zonal structure is similar to the historical response. In the lower stratosphere, the changes in water vapor and temperature due to projected future SSTs are of similar strength to, though slightly weaker than, that due directly to projected future CO 2 , ozone, and methane.

Nonlinear response of tropical lower stratospheric temperature and water vapor to ENSO

“…The evolution of cold point temperatures (defined in section 3) is overlaid on the water vapor evolution, and indicates that this drop in water vapor was due to a cooling of cold point temperatures. Hence, SST changes contributed to the drop (in agreement with Rosenlof and Reid, 2008), but were not the major forcing factor, consistent with Garfinkel et al (2013b) and Brinkop et al (2016). The rest of the drop is associated with the QBO and with BDC variability (Randel et al, 2006;Fueglistaler, 2012;15 Fueglistaler et al, 2014;Dessler et al, 2014).…”

“…Hence, an ENSO event that more efficiently warms the mid-troposphere (such as the 1997/1998 event) can more efficiently moisten the stratosphere. It has been suggested that SST changes in the Indo-Pacific contributed to some of the post-2000 drop in water vapor (Rosenlof and Reid, 2008;Garfinkel et al, 2013b) via ENSO (Brinkop et al, 2016), and here we consider whether the AGCM simulations simulate 8 Atmos. Chem.…”

Modifications of the quasi‐biennial oscillation by a geoengineering perturbation of the stratospheric aerosol layer

“…The increase in extends well above the level at which the diabatic heating ends, consistent with Holloway and Neelin [] and Garfinkel et al . [].…”

Seasonal evolution of the effects of the El Niño–Southern Oscillation on lower stratospheric water vapor: Delayed effects in late winter and early spring

“…Previous studies have demonstrated that El Niño events intensify the vertical propagation of ultra-long Rossby waves in the Northern Hemisphere during winter and thereby strengthen the BDC (Rao J et al, 2019a). This effect has been seen in observational records (Van Loon and Labitzke, 1987;Labitzke and Van Loon, 1989;Camp and Tung, 2007;Garfinkel and Hartmann, 2007;Free and Seidel, 2009) and has been reproduced in modeling studies (Hamilton, 1993;Sassi et al, 2004;García-Herrera et al, 2006;Manzini et al, 2006;Taguchi and Hartmann, 2006;Xie F et al, 2012;Garfinkel et al, 2013b;Rao J and Ren RC, 2016Rao J et al, 2019a, b, c). Therefore, we focused on the planetary wave activity during ENSO events that peak in the winter and decay in the spring.…”