Case study of stratospheric intrusion above Hampton, Virginia: Lidar-observation and modeling analysis

Abstract

On 2019-02-14, at 1:00 UTC, a large increase of ozone density at 8 km altitude was detected above Hampton, Virginia using the NASA Langley Mobile Ozone Lidar, LMOL. Ozone levels above 70 ppbv were observed down to an altitude of 4.5 km up to 5 h after the start of the event. The NASA GEOS Composition Forecast (GEOS-CF) model was used to investigate the hypothesis of a stratospheric intrusion (SI). The agreement between the model and the observations confirmed the stratospheric origin of the airmass and highlighted the capabilities of GEOS-CF to simulate intrusions. In parallel, MicroPulse Lidar (MPL) observations indicated that depolarizing particulates high in the troposphere showed downward motions linked to the intrusion. Since these particulates are linked to cirrus clouds, it is hypothesised that the SI led to an ice-virga effect. This might suggest that particulate observations can exhibit patterns of stratospheric intrusions and can be used, in certain cases, as a signature of the events. These particulates, likely ice crystals, have opposite distribution gradients compared to O3 at their interface which could be explained by a non-mixing of stratospheric and tropospheric air-masses as well as destruction of O3 by ice crystal-induced processes. Model-data comparison shows that if that latter effect exists, it has small consequences for the observed case. This work shows the capabilities of the LMOL system to detect SI and to validate the vertical and temporal modeling of SI by GEOS-CF, as well as showing that signatures of SI could be detected by MPL.