A case study of convectively sourced water vapor observed in the overworld stratosphere over the United States

Abstract

On 27 August 2013, during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys field mission, NASA's ER‐2 research aircraft encountered a region of enhanced water vapor, extending over a depth of approximately 2 km and a minimum areal extent of 20,000 km2 in the stratosphere (375 K to 415 K potential temperature), south of the Great Lakes (42°N, 90°W). Water vapor mixing ratios in this plume, measured by the Harvard Water Vapor instrument, constitute the highest values recorded in situ at these potential temperatures and latitudes. An analysis of geostationary satellite imagery in combination with trajectory calculations links this water vapor enhancement to its source, a deep tropopause‐penetrating convective storm system that developed over Minnesota 20 h prior to the aircraft plume encounter. High resolution, ground‐based radar data reveal that this system was composed of multiple individual storms, each with convective turrets that extended to a maximum of ~4 km above the tropopause level for several hours. In situ water vapor data show that this storm system irreversibly delivered between 6.6 kt and 13.5 kt of water to the stratosphere. This constitutes a 20–25% increase in water vapor abundance in a column extending from 115 hP to 70 hPa over the plume area. Both in situ and satellite climatologies show a high frequency of localized water vapor enhancements over the central U.S. in summer, suggesting that deep convection can contribute to the stratospheric water budget over this region and season.

Enhanced stratospheric water vapor over the summertime continental United States and the role of overshooting convection

“…These dates are 8, 16 and 27 August 2013. Similar results are seen from other hygrometers on the NASA ER-2 aircraft (Smith et al, 2015). For each of these ER-2 flights, the back trajectories are presented along with the intersection of coincident OT.…”

“…Enhanced water vapor measured in situ by both the JLH Mark2 instrument ( Fig. 1) and the Harvard Water Vapor instrument (Smith et al, 2015) on the NASA ER-2 aircraft indicated that the aircraft intercepted convectively influenced air. Other tracers measured on the aircraft did not change significantly in these plumes.…”

Modeling the Effect of Potential Nitric Acid Removal During Convective Injection of Water Vapor Over the Central United States on the Chemical Composition of the Lower Stratosphere

“…Observations of meteorological conditions in the midlatitudes have indicated the potential for chlorine activation and halogen‐catalyzed ozone loss in the lower stratosphere during the summer. Water vapor enhancements resulting from transport by tropopause‐penetrating convection, a consistent product of the unique climate of the summertime Central United States (Anderson et al, ; Anderson et al, ; Dessler & Sherwood, ; Hanisco et al, ; Ray et al, ; Schwartz et al, ; Smith et al, ; Sun & Huang, ; Toon et al, ; E. M. Weinstock et al, ), can move the conditions of the lower stratosphere into a state favorable to halogen activation and ozone loss particularly when low temperatures are present. The sensitivity of the lower stratosphere to convective water vapor enhancements is a direct result of the chlorine activation heterogeneous chemistry that is favored by high humidity, low temperatures, and larger sulfate aerosol surface area density (SAD; Anderson et al, ; Anderson et al, ; Anderson & Clapp, ; Carslaw et al, ; Drdla & Müller, ; Hanson, ; Horn et al, ; Murphy & Ravishankara, ; Portmann et al, ; Shi et al, ; S. Solomon et al, ; S. Solomon, ; Tabazadeh et al, ).…”

“…Observations of water vapor enhancements in coherent plumes have also been made up to between 7 and 12 days after convective injection (Pittman et al, ; Ray et al, ; Weinstock et al, ). Observations of a convectively sourced stratospheric water vapor plume show a minimum special extent of 20,000 km 2 between the pressure levels of 70 and 115 hPa and estimate a potentially more realistic area of up to 100,000 km 2 at 115 hPa given the exponential altitude dependence of convective volumes in the lower stratosphere (Smith et al, ).…”

“…Previous studies have shown the potential for chlorine activation and ozone loss in the midlatitudes due to heterogeneous chemistry on cirrus cloud particles in the UTLS (Borrmann et al, ; Borrmann et al, ; Solomon et al, ). Many observations of elevated water vapor have been made in the midlatitudes lower stratosphere, however, in the absence of cirrus clouds (Hanisco et al, ; Hegglin et al, ; Randel et al, ; Ray et al, ; Smith et al, ; Weinstock et al, ). Additional studies then extended the sensitivity of the summertime Central United States lower stratospheric heterogeneous chlorine activation and ozone loss to water‐sulfate aerosol surfaces resulting from such observed water vapor enhancements without cirrus cloud formation (Anderson et al, ;Anderson et al, ; Anderson & Clapp, ).…”