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The Asian Tropopause Aerosol layer (ATAL): Physical and chemical properties derived from in-situ aircraft borne measurements
Dec. 03, 2019, 15:00 - 16:00
KIT, Campus Nord, IMK-ASF, Gebäude 435, Seminarraum 2.05

During the Asian and West African monsoons large meteorological structures

develop which reach into the upper troposphere and lower stratosphere (UTLS)

with impact on the aerosols and the precursor gases entering the


Embedded in the Easterly flow in West Africa these are widespread fields of

Mesoscale Convective Systems (MCS) which reach altitudes of 16 to 18 km.

Further Northeast the Asian Monsoon Anticyclone (AMA) forms from mid-June

until October in an altitude band from roughly 12 to 20 km. The AMA extends

from East Asia to the Middle East and, as a fairly closed rotating air mass,

it is reminiscent of the polar vortex, albeit with a strong convective


Long range transport from as far as India and Eastern China provides

materials which are carried aloft by the deep convective (DC) AMA clouds in

the Himalaya region, similarly by the West African MCS. Sources (e.g.,

biomass burning) from the regional boundary layers also contribute here. The

anvil outflows of the West African MCS and the AMA DC clouds release the

uplifted (and partly processed) source gases and aerosols into the UTLS.

Here New Particle Formation events (NPF) generate new aerosols from the

inorganic and organic precursors by homogeneous nucleation.  Such NPF occur

in clear, cloud free air, as well as in the presence of ice particles in the

margins of Cumulonimbus clouds and MCS anvils. CALIPSO measurements revealed

a distinct aerosol layer (i.e., the Asian Tropopause Aerosol Layer; ATAL)

between 15 and 16.5 km within the AMA, the physical and chemical

characteristics of which still were unclear.  Since these phenomena occur at

the tropopause in areas with slow upwelling motion, they may contribute to

the global stratospheric aerosol. During the 2017 StratoClim field campaign

the Russian high altitude research aircraft M-55 “Geophysica” operated in

the AMA and ATAL at altitudes up to 20 km. Extensive in-situ chemical

composition measurements were performed on the submicron ambient aerosol

adopting a newly developed aerosol mass spectrometer. This new instrument

combines the two available techniques for particle mass spectrometry (i.e.

(1.) laser ablation and (2.) flash vaporization/electron impact ionization)

in one apparatus. These complementary methods provide both, qualitative and

quantitative information on the chemical composition of the sampled aerosol

in real time by direct reading. In addition a four channel condensation

particle counter provided measurements of number concentration and

volatility of aerosol particles as small as 6 nm. Also a modified UHSAS

optical particle counter was operated on “Geophysica” delivering aerosol

size distributions from 60 nm to 1 micrometer particle diameter. Some of the

key results from the 2017 StratoClim campaign in Nepal are discussed in the

presentation and juxtaposed to high altitude “Geophysica” measurements from

the West African monsoon.

This event is part of the eventgroup Meteorology Colloquium Karlsruhe
Prof. Dr. Stephan Borrmann
Johannes-Gutenberg-University/ Leader at Max-Planck-Institute for Chemistry
IMK-ASF Administration
Tel: +49 721 608-28271
Mail:sofia frankRta9∂kit edu
Scientific Staff
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