Antarctic Climate and Atmospheric Circulation

Project Description
Antarctica is the primary heat sink in the global climate system, and plays an important role in climate change and variability. Projections of the state of global change (e.g., global warming, ozone depletion) must accurately account for Antarctic atmospheric processes whose effects are transmitted to the rest of the planet via the atmosphere and the ocean. In addition, the processes by which tropical latitudes impact Antarctic are not well understood.

As a means to improve our understanding of atmospheric processes and transports between Antarctica and lower latitudes, a basic and applied research program is proposed to explore these atmospheric processes in detail. AC Squared will consist of both observational and modeling components with the fundamental goals to study the physical processes associated with transports throughout atmospheric column from the near-surface layer to the lower stratosphere and examine modulation of those transports during episodes of extratropical cyclone forcing, to accurately simulate these processes within numerical models, and to understand the mechanisms that produce teleconnections from the tropics and Antarctica, especially the interaction between the Southern Annular Mode and the El Nino-Southern Oscillation. As an additional benefit, AC Squared will advance short term to medium range weather forecasting in the high southern latitudes. It is believed that proper representation of Antarctic processes is prerequisite to accurate climate studies, especially since Antarctic transports are strongly tied to local topographic and mesoscale processes that are currently not resolved within GCMs. It is therefore necessary to understand local and regional processes before these effects can be assimilated into GCMs and global change issues can be considered. A series of objectives have been set for AC Squared that are deemed necessary before climate sensitivity issues can be addressed:

• Objective 1: To better understand key phenomena such as boundary-layer dynamics, topographic modification of synoptic and mesoscale features, cloud-radiation interactions, and moist processes accompanying episodes of cyclonic activity over the Southern Ocean adjacent to Antarctica that are associated with interactions between Antarctica and lower latitudes.
• Objective 2: To examine key processes associated with the dynamics and chemistry of the lower stratosphere including development of polar stratospheric clouds (PSCs), conduct field observations and in-situ measurements of chemical species and transports and modulation by large-scale dynamics processes.
• Objective 3: To conduct detailed measurements of key physical processes in the boundary layer and free atmosphere to permit the development of accurate parameterization schemes for use within numerical models, leading to high quality simulations of the atmospheric interactions.
• Objective 4: To investigate the nature of atmospheric teleconnections and their modulation of the atmospheric interactions between Antarctica and lower latitudes using numerical models, atmospheric reanalyses, and satellite observations

Objectives 1 and 2 will rely primarily on observations from the state-of-the-art HIAPER research aircraft flown out of Punta Arenas, Chile and southern New Zealand. Studies will be concentrated over the Weddell and Ross Sea embayments and areas to the north in association with the Schwerdtfeger Air Stream (SAS) and the Ross Air Stream (RAS), respectively. Satellite observations show PSCs to form frequently in the Weddell Sea area and airborne measurements will be conducted in the lower stratosphere in support of studies of transport dynamics of key chemical species.

Objective 3 will rely on a combination of airborne and ground-based measurements that will likely be concentrated in the Ross Sea vicinity. Attempts are being made to use fixed wing research aircraft such as the British Twin Otter or Twin Otters currently used in support of U.S operations for low-level measurements.

Objective 4 has a strong climate component and objective 1 can be thought of as case studies of the phenomena studied over a much longer period by this objective.

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