Identification

Title

Seasonal differences of vertical-transport efficiency in the tropical tropopause layer: On the interplay between tropical deep convection, large-scale vertical ascent, and horizontal circulations

Abstract

Winter-summer differences in the transport of air from the boundary layer to the lower stratosphere at low latitudes are investigated with ensembles of back trajectory calculations that track parcels from the 380 K isentropic surface to their convective detrainment in the tropical tropopause layer (TTL) during the winter of 2006-2007 and summer of 2007. Horizontal displacements for the trajectories are calculated from reanalysis data; potential temperature displacements are calculated from radiative heating rates derived from observed cloud, water vapor, ozone, and temperature variations; and the locations' convective detrainments are determined by satellite observations of convective clouds. Weaker upwelling in the TTL during boreal summer compared with that of winter both slows the ascent through the TTL and raises the height threshold that convective detrainment must surpass in order for ascent to occur, restricting the injection of new air into the stratosphere during summer. In addition, anticyclonic circulations associated with convective activity contribute to vertical transport in the TTL by guiding detrained air parcels through regions with the strongest upwelling. These features combine to make monsoon-related convection over the Indian subcontinent the dominant source of new air during summer. In contrast, winter sources are spread over the southern continents and the western Pacific Ocean. These seasonal differences imply that air entering the tropical stratosphere during summer is older but might nevertheless be more polluted than air entering during winter. While poor data sampling in the TTL makes it difficult to validate our results, they are bolstered by favorable comparisons with previous studies of the TTL, by sensitivity tests that reveal important dynamical influences on surface-to-stratospheric transport, and by the robustness of dynamical interactions that systematically associate deep convection with anticyclonic circulations and strong radiative heating in the TTL. Sensitivity experiments suggest that the aforementioned seasonal differences are sensitive to strong "large-scale" (on global space scales and seasonal time scales) perturbations. In particular, uncertainties in the vertical motion fields constrain our ability to draw definitive conclusions. However, trajectory statistics are not sensitive to small-scale perturbations, with the encouraging implication that our results are primarily associated with those features of the circulation that are the most likely to be robust.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7mw2hvv

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2012-03-03T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact