Impacts of the Indo‐Pacific Warm Pool on Lower Stratospheric Water Vapor: Seasonality and Hemispheric Contrasts

Abstract

Global mean surface temperature warmed by about 0.12°C per decade from the 1950s to 2000 most likely in response to significant increases in anthropogenic carbon dioxide and other greenhouse gases (IPCC, 2013). As an important greenhouse gas (GHG), stratospheric water vapor (SWV) contributes substantially to global climate change by altering the infrared opacity of the atmosphere (e.g., Soden & Held, 2006), providing strong positive feedback to global warming at +0.3 W/(m 2 •K) (Dessler et al., 2013). Sensitivity studies of climate models have demonstrated that even a small increase in the lower SWV can lead to marked changes in radiative forcing, resulting in cooling of the lower stratosphere (

Stratospheric Aerosol and Ozone Responses to the Hunga Tonga‐Hunga Ha'apai Volcanic Eruption

“…Then, the weakened circumpolar circulation could lead to a complete entry of planetary waves 1 and 2 into the stratosphere (Figures 4e–4f, Figure S8 in Supporting Information ). The upward EP flux difference at 60–90°S (Figures 4a and 4b) also indicated more planetary waves enter the stratosphere, which led to a stronger vertical transport (Eguchi et al., 2015; Lu et al., 2021; Xie et al., 2018; Zhou et al., 2021). The enhanced upwelling of the BD circulation (Figures 3c and 3d) resulted in a negative polar low‐stratospheric O 3 anomaly (Figures 3c and 3d).…”

Contrasting Effects of Indian Ocean Basin and Dipole Modes on the Stratosphere

“…Consequently, more negative SWV anomalies are in the regions north of 20°N in the lower stratosphere in SON (Figure 6a). Previous research also indicates the importance of CPR temperature and morphology on the lower SWV Zhou et al, 2021). The transport of lower SWV to the middle and upper stratosphere is complicated, owing to the existence of seasonal variability in lower water vapor sources (Figures 4 and 6a) and the certain time scales for water vapor rise (Figure 6b).…”

“…The results are not sensitive to change this 10% threshold. The temperature of CPR is a rough approximation to the coldest temperature an air parcel experienced Garfinkel et al, 2018) and the seasonal movement of the CPR position is basically coinciding with that of the climatological convective activity location (Highwood & Hoskins, 1998;Randel & Park, 2019;Rosenlof et al, 1997;Zhou et al, 2021).…”

“…It is noteworthy that CPTT displays significant cold anomalies during the summer (Jun-Jul-Aug; JJA), despite minimal concomitant changes in SWV (Figures 4b and 4j). In JJA, the main convective activities occur over the Indian and Asian monsoon regions (Highwood & Hoskins, 1998;Randel & Park, 2019;Rosenlof et al, 1997;Zhou et al, 2021). Therefore, the significant CPTT variations over the tropical Indian Ocean have a relative weaker impact on SWV at 85 hPa in JJA than they do in SON.…”

“…Second, why do the IOBM result in complex interhemispheric SWV responses in middle-high stratosphere? Since previous studies have confirmed that the relationship between tropical SST and SWV entry exhibits a pronounced seasonal dependence Garfinkel et al, 2018;Zhou et al, 2021), it is vital to consider the seasonality when investigating the influences of the two Indian Ocean modes on SWV.…”