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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 9 | Copyright
Atmos. Chem. Phys., 17, 6113-6124, 2017
https://doi.org/10.5194/acp-17-6113-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 May 2017

Research article | 17 May 2017

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

Robert L. Herman1, Eric A. Ray2, Karen H. Rosenlof2, Kristopher M. Bedka3, Michael J. Schwartz1, William G. Read1, Robert F. Troy1, Keith Chin1, Lance E. Christensen1, Dejian Fu1, Robert A. Stachnik1, T. Paul Bui4, and Jonathan M. Dean-Day5 Robert L. Herman et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 2National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL) Chemical Sciences Division, Boulder, Colorado, USA
  • 3NASA Langley Research Center, Hampton, Virginia, USA
  • 4NASA Ames Research Center, Moffett Field, California, USA
  • 5Bay Area Environmental Research Institute, Sonoma, California, USA

Abstract. The NASA ER-2 aircraft sampled the lower stratosphere over North America during the field mission for the NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS). This study reports observations of convectively influenced air parcels with enhanced water vapor in the overworld stratosphere over the summertime continental United States and investigates three case studies in detail. Water vapor mixing ratios greater than 10ppmv, which is much higher than the background 4 to 6ppmv of the overworld stratosphere, were measured by the JPL Laser Hygrometer (JLH Mark2) at altitudes between 16.0 and 17.5km (potential temperatures of approximately 380 to 410K). Overshooting cloud tops (OTs) are identified from a SEAC4RS OT detection product based on satellite infrared window channel brightness temperature gradients. Through trajectory analysis, we make the connection between these in situ water measurements and OT. Back trajectory analysis ties enhanced water to OT 1 to 7 days prior to the intercept by the aircraft. The trajectory paths are dominated by the North American monsoon (NAM) anticyclonic circulation. This connection suggests that ice is convectively transported to the overworld stratosphere in OT events and subsequently sublimated; such events may irreversibly enhance stratospheric water vapor in the summer over Mexico and the United States. A regional context is provided by water observations from the Aura Microwave Limb Sounder (MLS).

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This study reports new aircraft field observations of elevated water vapor greater than 10 ppmv in the overworld stratosphere over the summertime continental US. Back trajectories from the flight track intersect overshooting convective tops within the previous 1 to 7 days, suggesting that ice is convectively and irreversibly transported to the stratosphere in the most energetic overshooting convective events. Satellite measurements (Aura MLS) indicate that such events are uncommon (< 1 %).
This study reports new aircraft field observations of elevated water vapor greater than 10 ppmv...
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