Asian monsoon Tropical Tropopause Layer: transport and composition – TTL-Xing

We will use new geostationary satellites enabling advanced retrieval algorithms, the active space lidars combined with radars and the recent progresses in retrieving cirrus properties from hyperspectral sounders, in order to characterize the distribution of high clouds in the Asian monsoon.
We will add new measurements to monitor the evolution of the ATAL and we will determine its global impact using the global NDACC network.
Radiative calculations will exploit this distribution to determine the radiative effect of clouds in this region.
A state of the art cloud resolving model and a general circulation model, both with comprehensive chemistry will be used to understand the processes of the ATAL and provide some guide on its sources, its global impact and its likely evolution under climate change.
Extensive Lagrangian calculation coupled with microphysical modelling will complement the modeling effort to study large scale impact on one side and to exploit and interpret the small-scale observations on the other side.
These actions will exploit the unique dataset collected by the very successful StratoClim airborne campaign in 2017 to which several members of the team have been closely associated. The campaign has brought an unparalleled dataset that includes full determination of the composition of the ATAL and its gas precursors, and a wealth of observations of the high clouds in the Asian monsoon.

The Lagrangian trajectories have shown that the ubiquitous ATAL nitate compounds and ammonium gas observed during StratoClim are related to the intense agriculture practiced in the Gange and Indus valleys.
The analysis of water and ice data shows an exceptional variety of situations, sometimes during the same flight, that result in either hydration or dehydration at the top of convective clouds.
We have explained the anticyclone confinement and the regional impact of convection at high altitude (above 370K potential temperature) by a simple 1D advective model with loss.
The comparison of meteorological reanalysis (often used as a reference in climate studies) exhibit essential differences in the cloud properties, due to ice parametrization, which are reinforced in the monsoon area.
We have shown the excellent ability of the MesoNH model to reproduce the observed monsoon convection and its impact at high altitude.
We have established a database of physical and radiative properties of the high clouds based on the IR sounders.
We have shown that the circulation around the Asian monsoon anticyclone can redistribute compounds of volcanic of forest-fire plumes towards the low latitudes.
The persistence and large variability of the ATAL have been established both from the observations and from modelling studies.

In the short term, during the second phase of the project, we will consolidate the results of the first phase and extend the studies to evaluate the large scale and the anthropogenic impacts.

Feofilov, A. G., C. J. Stubenrauch, Diurnal variation of high-level clouds from the synergy of AIRS and IASI space-borne infrared sounders Atmosph. Chem. Phys. Discuss., 10.5194/acp-2019-166 in revision (2019).

Hemmer, F., C. J. Stubenrauch, and S. E. Protopapadaki, Predicting 3D Radiative Heating Rate Fields from Synergistic A-Train Observations combined with Deep Learning Techniques, 9th International Workshop on Climate Informatics Proceedings, 2-4 Oct. 2019, Paris

Höpfner, M., Ungermann, J., Borrmann, S., Wagner, R., Spang, R., Riese, M., Stiller, G., Appel, O., Batenburg, A. M., Bucci, S., Cairo, ..., Legras, B., et al., I.: Ammonium nitrate particles formed in upper troposphere from ground ammonia sources during Asian monsoons, Nat. Geosci., 12(8), 608–612, doi:10.1038/s41561-019-0385-8, 2019.

Kloss, Corinna, Gwenaël Berthet, Pasquale Sellitto, Felix Ploeger, Silvia Bucci, Sergey Khaykin, Fabrice Jégou, Ghassan Taha, Larry Thomason, Brice Barret, Eric Le Flochmoen, Marc von Hobe, Adriana Bossolasco, Nelson Begue, Bernard Legras, Transport of the 2017 Canadian wildfire plume to the tropics and global stratosphere via the Asian monsoon circulation, ACP Discussions, en révision, doi.org/10.5194/acp-2019-204, 2019.
Stubenrauch, C. J., M. Bonazzola, S. E. Protopapadaki and I. Musat, New Cloud System Metrics to Assess Bulk Ice Cloud Schemes in a GCM, J. Advanc. Model. Earth Sys., in press (2019).

Tegtmeier, S., Anstey, J., Davis, S., Dragani, R., Harada, Y., Ivanciu, I., Pilch Kedzierski, R., Krüger, K., Legras, B., Long, C., Wang, J. S., Wargan, K. and Wright, J. S.: The tropical tropopause layer in reanalysis data sets, Atmos. Chem. Phys. Discuss., 1–28, doi:10.5194/acp-2019-580, 2019.

Vernier, Jean-Paul, …, Gwenaël Berthet; Fabrice Jégou; Jean-Baptiste Renard; Travis Knepp; Luke Ziemba; Suneel Kumar, BATAL: The Balloon measurement campaigns of the Asian Tropopause Aerosol Layer, Bull. Met. Am. Soc., doi.org/10.1175/BAMS-D-17-0014.1, 2018.

The Tropical Tropopause Layer (TTL) is the region of the atmosphere between 30S and 30N which is bounded by the convectively dominated tropical troposphere below and the layered motion in the stratosphere regulated by the Brewer Dobson circulation above. The TTL is the gateway which processes the air lofted from the surface by convection, including anthropogenic pollution, and controls the composition of the stratosphere. Due to this role and the radiative effects of its ubiquitous cirrus clouds, which are regulating the convection underneath, the TTL is a key component of the climate system.
During summer, the TTL is mostly under the influence of the Asian monsoon where the upper layer circulation is dominated by a large anticyclone extending from east Asia to the Mediterranean sea. This circulation ventilates the convection and redistributes the lofted air. Since two decades, a new aerosol layer (ATAL=Asian Tropopause Aerosol Layer), recently discovered, has developed near 16 km altitude inside the monsoon anticyclone and is attributed to the growing anthropogenic emissions at the ground.
The impact of the monsoon on the TTL and the stratosphere, the distribution of ground sources, the transport properties across the TTL and the processes related to aerosols and cirrus within the TTL, in particular the ATAL, are still poorly known due to a lack of available observations and limited modeling studies. However, a wealth of new observations is now being provided by a new generation of satellite instruments and a series of campaigns in Asia based on international collaboration. The EU funded StratoClim airborne campaign in 2017 will provide a large amount of unparalleled in situ observations within the Asian monsoon TTL and the ATAL.
The overarching goal of our project is to understand how does climate change affect the features of the TTL (cirrus, radiative budget and composition of the air entering the stratosphere) during the Asian monsoon season and what is the feedback on the climate. The investigated questions in this proposal are (i) the description of high altitude clouds and of their injection of water and tracer compounds in the TTL, (ii) the processes from small to large scale which regulate transport, the distribution of cirrus and aerosol, (iii) the radiative impact of clouds, in particular the thin cirrus, and aerosols in the Monsoon region, (iv) the full exploitation of available data. An immediate urgent question is to understand the change in composition manifested by the ATAL, to determine its chemical and physical properties, to understand and monitor the sources and precursors and to determine its direct and indirect glaciation radiative forcing and the induced modulation of stratospheric composition.
These questions will be answered by a coordinate set of tasks. Multi-satellite data will be analyzed to determine the properties of high altitude clouds and aerosols. The StratoClim campaign data will be exploited using Lagrangian modeling methods to link the measurements to the sources and the history of air parcels. We will a new set of observations by light weight innovative instruments flying under small balloons and ATAL impact will be monitored by the ground-based lidars of the NDACC network.Two complementary models with full representation of chemical and micro-physical processes will be used to reproduce the ATAL and compared with the campaign and satellite data. Climatologies of relevant ground sources and transport pathways will be established. Climate change projections will be estimated.
Our project will be conducted by a team that gathers the highest expertise in atmospheric modeling, observation and data analysis and is already well trained to work together. Our project is a unique opportunity to make the best usage of the most recent observations and to produce major advances on a key issue in climate science.