The Spread of the Hunga Tonga H₂O Plume in the Middle Atmosphere Over the First Two Years Since Eruption

Abstract

The eruption of Hunga in January 2022 injected a large amount of water into the stratosphere. Satellite measurements from Aura Microwave Limb Sounder (MLS) show that this water vapor (H2O) has now spread throughout the stratosphere and into the lower mesosphere, resulting in an increase of >1 ppmv throughout most of this region. Measurements from three ground‐based Water Vapor Millimeter Wave Spectrometer (WVMS) instruments and MLS are in good agreement, and show that in 2023 there was more H2O in the lower mesosphere than at any time since the WVMS measurements began in the 1990's. At Table Mountain, California all WVMS H2O measurements at 54 km since June 2023, and all of the measurements from Mauna Loa, Hawaii, since the resumption of measurements in September 2023, show larger mixing ratios than any previous measurements. At 70 km several recent WVMS retrievals since September 2023 show the largest anomalies ever measured. The MLS measurements show that maximum H2O anomalies over the 2004–2023 record have occurred throughout almost all of the stratosphere and lower mesosphere since the eruption. As of November 2023, almost all of the ∼140 Tg of water originally injected into the stratosphere by the Hunga eruption remains in the middle atmosphere at pressures below 83 hPa (altitudes above ∼17 km). The eruption occurred during a period when stratospheric H2O was already slightly elevated above the 2004–2021 MLS average, and the November 2023 anomaly of ∼160 Tg represents ∼15% of the total mass of H2O in this region.