Influence of sudden stratospheric warming with elevated stratopause on the hydroxyl in the polar middle atmosphere

Abstract. Based on the specified dynamics simulation of Whole Atmosphere Community Climate Model with ionosphere/thermosphere extension (SD-WACCM-X), the composite response of polar hydroxyl radical (OH) layer in the mesosphere and lower thermosphere (MLT) to the Arctic sudden stratospheric warming (SSW) events with elevated stratopause (ES) during 2004–2023 is investigated. A total of ten ES-SSW events are systematically analyzed. Before the onset of ES-SSW events, the OH concentration climatologically peaks at ∼ 7.4 ppbv near 82.4 km. During the stratospheric warming phase, relative to the climatology, the peak height of OH layer undergoes a distinct upward displacement reaching ∼ 85.9 km accompanied by a reduction in the OH concentration to ∼ 2.9 ppbv. This shift is closely linked to an ∼ 11 % and ∼ 90.8 % reduction in mesospheric temperature and atomic oxygen, respectively, due to enhanced upward residual circulation. During the elevated stratopause phase, the peak height of OH layer experiences a pronounced downward shift to ∼ 80.6 km with a maximum in OH concentration to ∼ 6.8 ppbv. This phase is characterized by ∼ 3.7 % and ∼ 137.3 % enhancements in mesospheric temperature and atomic oxygen concentrations, respectively, which is driven by intensified downward residual circulation. Further analysis suggests that OH concentration variations are positively correlated to mesospheric temperature anomalies and atomic oxygen redistribution induced by vertical transport, which is attributed to the significant influence of ES-SSW on gravity wave drag (GWs) in the mesosphere.