Constraining Supersaturation and Transport Processes in a South American Cold-Air Outbreak Using Stable Isotopologues of Water Vapor

In situ measurements of water vapor isotopic composition from the subtropical Chilean Andes, supported by mesoscale model simulations and diagnostic analyses, document the processes governing the transport of dry air and isotopically depleted water vapor from the midlatitudes into the subtropics dur...

Full description

Saved in:
Bibliographic Details
Published in:Journal of the atmospheric sciences 2015-05, Vol.72 (5), p.2055-2069
Main Author: Galewsky, Joseph
Format: Article
Language:English
Subjects:
Atmospherics
Cold
Computer simulation
Depletion
Ice
In situ measurement
Isotopes
Marine
Outbreaks
Remote sensing
Studies
Supersaturation
Surges
Temperature
Transport
Transport processes
Water vapor
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:In situ measurements of water vapor isotopic composition from the subtropical Chilean Andes, supported by mesoscale model simulations and diagnostic analyses, document the processes governing the transport of dry air and isotopically depleted water vapor from the midlatitudes into the subtropics during a South American cold-air surge in July 2014. On 23 July 2014, temperatures on the Chajnantor Plateau reached -18 degree C, among the lowest temperatures on record for the site. On 26 July 2014, water vapor delta D and delta super(18)O reached a low of -538 plus or minus 1.6ppt and -71.7 plus or minus 0.2ppt, among the lowest values on record. Numerical simulations show that the dynamics of the event were consistent with previous studies of South American cold-air outbreaks. Back-trajectory analyses show that the isotopically depleted water vapor that reached Chajnantor on July 26 was last saturated over the South Pacific on July 23 at 300 hPa at a temperature of about -50 degree C under ice supersaturation with RH sub(ice) of about 110%. The water vapor traveled to Chajnantor along a nearly isentropic path following saturation. Modeling of the isotopic data require condensation at temperatures between -50 degree C and -53 degree C under supersaturation with RH sub(ice) between 112% and 118%, followed by less than 25% moistening during transport. These results show that measurements of water vapor isotopic composition can provide observational constraints on in-cloud processes that influence the humidity of the subtropics.
ISSN:0022-4928
1520-0469
DOI:10.1175/JAS-D-14-0352.1