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

Abstract

Water vapor in the stratosphere makes a significant contribution to global climate change by altering the radiative energy budget of the Earth's climate system. Although many previous studies have shown that the El Niño–Southern Oscillation (ENSO) has significant effects on the water vapor content of the stratosphere in terms of the annual or seasonal mean, a comprehensive analysis of the seasonal evolution of these effects is still required. Using reanalysis data and satellite observations, we carried out a composite analysis of the seasonal evolution of stratospheric water vapor during El Niño/La Niña peaks in winter and decays in spring. The ENSO has a distinct hysteresis effect on water vapor in the tropical lower stratosphere. The El Niño/La Niña events moisten/dry out the tropical lower stratosphere in both winter and spring, whereas this wetting/dehydration effect is more significant in spring. This pattern is due to a warmer temperature in the upper troposphere and lower stratosphere during the El Niño spring phase, which causes more water vapor to enter the stratosphere, and vice versa for La Niña. This delayed warming/cooling in the lower stratosphere during the El Niño/La Niña decay in spring leads to the seasonal evolution of ENSO effects on water vapor in the lower stratosphere.

Significant Stratospheric Moistening Following Extreme El Niño Events

“…On the contrary, during moderate El Niño winters, dipole-shaped wet and dry regions of comparable intensity are observed in the Indo-Western Pacific and Central-Eastern Pacific, respectively. This is similar to the previously observed annual average distribution of 100 hPa water vapor in response to the El Niño signal [30,31,43], i.e., cooling in the tropical central-eastern Pacific at 100 hPa is accompanied by negative water vapor anomalies, while warming in the western Pacific corresponds to positive water vapor anomalies. However, unlike the distribution of annual mean water vapor anomalies, the wetness of the western Pacific is comparable to the dryness of the central-eastern Pacific during the winter of moderate El Niño; thus, the net impact of water vapor in the lower stratosphere tends to be zero after zonally averaged.…”

“…Furthermore, our previous study [43] proposed that the impact of ENSO on stratospheric water vapor is more pronounced in spring as a result of the lag in stratospheric response to ENSO signals. In this study, we found that only moderate El Niño events exhibit a lagged effect, while extreme events elicit a strong response in the stratosphere regardless of the season, which provides new insights for future research on extreme climate events.…”

“…Scaife et al [28] proposed as early as 2003 that El Niño causes a 10% increase in the concentration of water vapor entering the stratosphere. In contrast, during La Niña activity (the cold phase of ENSO), the relatively colder temperature in the upper troposphere may have a drying effect on the lower stratosphere in the tropics [42,43]. It is worth noting that a 2011 study by Xie et al [31] noted that this drying effect of La Niña on the lower stratosphere occurs primarily in a narrow band of 5 • S-5 • N in the tropics, whereas the entire stratosphere is wet for the wider tropics (25 • S-25 • N), which also serves as a reminder to pay attention to the zonal mean heterogeneity when analyzing the effect of La Niña activity on stratospheric water vapor.…”

Opposite Impacts of Interannual and Decadal Pacific Variability in the Extratropics

“…El Niño warms the cold point (Calvo et al, 2010;Free & Seidel, 2009;García-Herrera et al, 2006; W. J. Randel, Garcia, et al, 2009;Scaife et al, 2003) leading to an increase in SWV (Fueglistaler & Haynes, 2005;Garfinkel et al, 2013;Gettelman et al, 2001;Konopka et al, 2016;Liao et al, 2019;Lu et al, 2020;Randel et al, 2004;Scaife et al, 2003). Consistent with this, cold point temperatures (Figures 3b and 3c) and SWV (Figure 4a) both increase throughout the 10 year simulations.…”

“…The concentration of water vapor in the stratosphere varies on both interannual and multi‐decadal timescales (W. J. Randel, Garcia, et al., 2009; W. J. Randel, Shine, et al., 2009; Solomon et al., 2010; Yu et al., 2022). El Niño warms the cold point (Calvo et al., 2010; Free & Seidel, 2009; García‐Herrera et al., 2006; W. J. Randel, Garcia, et al., 2009; Scaife et al., 2003) leading to an increase in SWV (Fueglistaler & Haynes, 2005; Garfinkel et al., 2013; Gettelman et al., 2001; Konopka et al., 2016; Liao et al., 2019; Lu et al., 2020; Randel et al., 2004; Scaife et al., 2003). Consistent with this, cold point temperatures (Figures 3b and 3c) and SWV (Figure 4a) both increase throughout the 10 year simulations.…”