Antarctic Precipitation : Remote Sensing from Surface and Space – APRES3

There is no precipitation measurement network in Antarctica to evaluate the performances of climate models for this parameter. Yet all models predict an increase of precipitation. This is the single most important positive term of the ice sheet mass balance, and an increase of precipitation will moderate sea-level rise due to other contributions. However, models disagree as to the amplitude of this moderation. The 1st climatology of antarctic precipitation that allows an objective evaluation of models was recently assembled using CloudSat satellite radar data. The space – time coverage is partial though, and it should be completed using other satellite data. Also, data from field campaigns and in situ measurements are still in demand to properly calibrate and validate the new product. This is necessary to sort out models and select best predictions from the models that perform best for current climate.

APRES3 objectives are precisely, to test and adapt to Antarctica existing satellite precipitation retrieval methods using passive microwaves for one part, and to deploy and exploit the 1st in situ measurement campaigns in Antarctica for the calibration and validation of satellite precipitation products. APRES3 will also use the microphysical measurements of hydrometeors from in situ and surface remote sensing obtained during these campaigns, to evaluate and calibrate cold microphysics parametrizations for clouds and precipitation in meteorological and climate models. To reach these objectives, the project partnership brings together the complementary expertise of 3 French and 1 Swiss laboratories, the latter being self-funded, and collaboration with other foreign laboratories. One of the central expertise is on remote sensing of precipitation with radars and lidars. The experimental component of the project relies heavily on this expertise for the acquisition and exploiting of field measurements. It is the 1st time a multi-instrumented campaign is designed and deployed in Antarctica for the calibration and validation of satellite precipitation retrievals.

The project is structured along 5 tasks. Task 0 ensures project coordination and promotion while task 1 deals with the logistics for field activities. Deploying complex instruments in Antarctica raises significant logistical issues because the region is remote and the environment is harsh. Task 2 is a central component of the project. It will (1) propose a physically-based modelling framework for the vertical structure of hydrometeors based on multi-sensor data and (2) produce and exploit field data to infer common algorithms in both alpine and antarctic contexts. This will be used to validate CloudSat microphysical parameters retrievals from which precipitation is deduced. For this, APRES3 will collaborate with 2 US institutes expert in CloudSat radar remote sensing. Task3 will test and if possible adapt methods used elsewhere but not yet over Antarctica to detect precipitation using passive microwaves data from space. Task 3 will also compare the final satellite precipitation quantities against surface measurements from task 2. Task 4 is the meteorological and climate model application component. It is dedicated to evaluating cold microphysics parametrizations used in models to simulate clouds and precipitation, and to producing and analyzing climate predictions.

The main final deliverables are a calibrated and validated satellite climatology of antarctic precipitation, its use to evaluate and validate climate models, a synthesis of previsions of the contribution of antarctic precipitation to future sea-level change, all of this in time to contribute to the next IPCC report.