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 10 ppmv, which is much higher than the
background 4 to 6 ppmv of the overworld stratosphere, were measured by the
JPL Laser Hygrometer (JLH Mark2) at altitudes between 16.0 and 17.5 km
(potential temperatures of approximately 380 to 410 K). 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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