Responses of polar mesospheric clouds to water vapor anomalies caused by the 2022 Hunga Tonga–Hunga Ha’apai eruption

Abstract The H $$_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O plume, injected by the Hunga Tonga–Hunga Ha’apai (HTHH) eruption on 15 January 2022, spread and reached the high-latitude mesopause regions 2 years after the eruption. To investigate the relationships between polar mesospheric clouds (PMCs) and the HTHH eruption-originated H $$_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O anomalies, we have analyzed PMC occurrence rates (ORs), temperature, and water vapor volume mixing ratios (H $$_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O VMRs), based on observational data from Himawari-8/Advanced Himawari Imager (AHI), Himawari-9/AHI, and Aura/Microwave Limb Sounder. To focus the PMC responses to the H $$_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> O anomalies, we extracted the temperature-independent components in the PMC OR variability, which is defined as $${\Updelta }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> </mml:math> PMC. As a result, we found a significant $${\Updelta }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> </mml:math> PMC increase (15±5%) in January 2024 in the Southern Hemisphere (SH), which was associated with the HTHH eruption-induced water vapor increase (0.88±0.04 ppmv) at 77.8–87.9 km altitudes in January 2024 in the SH. The finding would be, for the first time, observational evidence of PMC variations induced by volcanic eruptions, which is a striking PMC topic that has long been discussed since the 1883 Krakatoa eruption. Graphic Abstract