Descent of Water Vapor from the Arctic Vortex to the Lowermost Stratosphere

Unusually high water vapor mixing ratios (>5.5 ppmv) are observed in AURA-MLS measurements in the lowermost stratosphere (~100 hPa) near in Eastern Russia in late February 2009. These high water vapor mixing ratios appear to come not upwards from the troposphere, but have their origin in the higher water vapor mixing ratios generally found near the stratopause. The median of the AURA-MLS water vapor measurements at mid- and high latitudes is ~4.6 ppmv, and the peak water vapor mixing ratio in the mesosphere is ~7 ppmv, so the fraction of the air in this high water vapor region at 100 hPa which originated in the mesosphere is ~40%. Using AURA-MLS data the Navy's Operational Global Atmospheric Prediction System Advanced Level Physics-High Altitude (NOGAPS-ALPHA) analysis, and trajectory calculations, we track this high water vapor feature from its origin in the Arctic Vortex down to ~100 hPa over a period of several weeks. From the end of January until the end of February trajectory calculations show that air parcels at a potential temperature of ~460K over North America were advected over the pole, and descended locally over Eastern Russia for about 2 weeks, eventually arriving at ~430K over Eastern Russia. The feature can be tracked in the NOGAPS assimilation, but temporarily disappears from the MLS data while it passes over the pole. MLS also measures high levels of ozone coincident with the high water vapor during this period.