![Hier klicken, um den Treffer aus der Auswahl zu entfernen](images/unchecked.gif) |
Titel |
Observations of TTL water vapor and cirrus properties from the NASA Global Hawk during the Airborne Tropical TRopopause EXperiment |
VerfasserIn |
Troy Thornberry, Andrew Rollins, Ru-Shan Gao, Sarah Woods, Paul Lawson, Thaopaul Bui, Leonhard Pfister, David Fahey |
Konferenz |
EGU General Assembly 2015
|
Medientyp |
Artikel
|
Sprache |
Englisch
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250107995
|
Publikation (Nr.) |
EGU/EGU2015-7724.pdf |
|
|
|
Zusammenfassung |
Despite its very low mixing ratios relative to the troposphere, water vapor in the lower
stratosphere (LS) plays a significant role in Earth’s radiative balance and climate system and
is an important constituent in stratospheric chemistry. The low H2O content of air
entering the LS is established to first order by dehydration processes controlled by
the cold temperatures of the tropical tropopause layer (TTL), especially over the
western Pacific. Cirrus clouds occur with high frequency and large spatial extent
in the TTL, and those occurring near the thermal tropopause facilitate the final
dehydration of stratosphere-bound air parcels. Uncertainties in aspects of the nucleation
and growth of cirrus cloud particles and the sparseness of in situ water vapor and
cirrus cloud observations with sufficient spatial resolution limit our ability to fully
describe the final stages of the dehydration process before air enters the LS in the
tropics.
The NASA Airborne Tropical TRopopause EXperiment (ATTREX) measurement
campaign has yielded more than 140 hours of sampling from the Global Hawk UAS in the
Pacific TTL during deployments in winter 2013 and 2014, including more than 30 hours
sampling TTL cirrus. Cirrus clouds were encountered throughout the TTL, up to the
tropopause (17-18 km), with ice water contents (IWC) down to the detection limit of 3 μg
m-3 and water vapor mixing ratios as low as 1.5 ppm. Most TTL cirrus sampled had particle
number concentrations of less than 100 L-1, but some had concentrations ranging up
to more than 1000 L-1. The mean value for relative humidity with respect to ice
within cirrus was near 100%, but encompassed a range from < 50% to higher than
150%. The high spatial and temporal resolution in situ measurements of water vapor
and cirrus cloud properties made during ATTREX provide an outstanding dataset
by which to characterize the Pacific TTL environment and evaluate our current
understanding of the dynamical and microphysical processes that result in the dehydration of
stratosphere-bound air in this region. Here we present an analysis of the ATTREX
water vapor, relative humidity and cirrus cloud ice crystal measurements and IWC
data to investigate cirrus cloud formation in the TTL and the resulting potential for
dehydration. |
|
|
|
|
|