May 1, 2012
CIRES student receives an AGU award
Adriana Raudzens Bailey, a CIRES graduate student, received the Outstanding Student Paper Award for her presentation at the 2011 American Geophysical Union (AGU) Fall Meeting in San Francisco, California. The honor, which was awarded by the AGU on behalf of the Atmospheric Sciences section, was for Bailey’s presentation “Isotopic signatures of mixing processes and cloud detrainment in the subtropics.”
ABSTRACT FINAL ID: A54A-06
TITLE: Isotopic signatures of mixing processes and cloud detrainment in the subtropics
SESSION TYPE: Oral
SESSION TITLE: A54A. Boundary-Layer Processes Above Land and Ocean III
AUTHORS (FIRST NAME, LAST NAME): Adriana Raudzens Bailey1, 2, David C Noone1, 2, Darin W Toohey1
INSTITUTIONS (ALL): 1. University of Colorado Boulder, Boulder, CO, United States.
2. Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States.
ABSTRACT BODY: Distributions of water vapor and cloud have the potential to effect significant feedbacks on changes in climate. This motivates a greater understanding of the hydrological processes that regulate atmospheric humidity and cloudiness, as well as key cloud parameters like albedo and lifetime. In this work, the signatures of large-scale condensation and local moisture exchange between cloud and environment are investigated in the subtropical mixed boundary layer and lower free troposphere using stable isotope ratios in water (D:H, 18O:16O). High-frequency (10-s) measurements of water isotope ratios and water mixing ratio were sampled over 4,000 meters in the vertical by driving a Picarro water vapor isotope analyzer from sea level to the summit of Mauna Kea, Hawai’i. Modeled profiles developed from isotope theory are used to test the thermodynamic conditions and mechanisms that set the humidity observed. Specifically, since isotopically heavy water exhibits a lower vapor pressure than normal water, the isotope ratios in vapor are depleted in a predictable way as water changes phase. Further exchange (equilibration) between vapor and the condensed cloud or rain affects the degree of depletion and reflects the precipitation efficiency of the system. Mixing line analyses clearly identify the boundary layer and free troposphere as distinct air masses and suggest mixing processes play an important role in linking these two layers. Spatial gradients of aerosol number size distribution within the transition region support this interpretation. However, in many profiles, multiple mixing lines indicate the complex role that water and clouds play above and below the trade wind inversion. Where the mixing line isotope ratios greatly exceed the isotope ratios of the environmental vapor, the possibility that vapor has been moistened by detrained cloud at the top of the trade wind inversion is investigated. Aerosol measurements provide an independent check on cloud processing. Results from Hawai’i are compared with airborne measurements made in July 2011 over the Caribbean as part of the Ice in Clouds Experiment –Tropical to examine profile similarities and differences between regions with topographic forcing and regions of free air, and between regions that are actively convecting and those that are not.