TWP-ICE Airborne and ground based observations network around Darwin

Tropical cirrus clouds are composed of ice crystals formed by the outflow from deep convective clouds. They play an important role in the atmosphere radiation balance and dominate the cloud radiative forcing in the tropics.

The Tropical Warm Pool International Cloud Experiment (TWP-ICE) was carried out near Darwin, during January-February 2006. Wing Ng and Zahra Bouya from the School of Physics were involved in this experiment. The main focus of the TWP-ICE was to collect data to be used to address a range of important scientific questions related to tropical convective clouds systems, their evolution and impact on the environment. The data collected provides the information required by cloud resolving models and parameterizations in Global Climate Models (GCMs) to improve their representation in such models.

TWP-ICE was undertaken over a four week period to coincide with the maximum rainfall and convective activity during the summer monsoon season in northern Australia. Darwin was selected because it was expected to be representative of conditions typical for wide areas of the tropics. Despite its coastal location, the convection that occurs at this time is largely of maritime origin with a large fetch over water.

The experiment was conducted near the US Department of Energy’s Atmospheric Radiation Measurement (ARM) Atmospheric and Climate Research facility in Darwin. Data from the TWP-ICE will complement data from the ARM permanent facility, which is equipped with sophisticated instruments providing long term continuous data to provide a detailed understanding of the tropical atmosphere.

The key component of the TWP-ICE was the fleet of aircraft: 5 instrumented aircraft (from the US Dept. of Energy, the UK NERC, Twin Otter International and Airborne Research Australia) flew at different altitudes to measure cloud properties. The ground network included a ship as well as several ground sites with a wide range of cloud sensing radar, lidar and passive instruments.

Radiosondes (weather balloons) were launched every three hours from five surface sites around the central location in Darwin (map above). The Southern Surveyor research vessel was equipped with surface based instruments and also a facility to launch the weather balloons.

Zahra worked in the experiment Headquarters in the main Darwin control area on the daily scientific summaries under the guidance of the ARM chief scientist Tom Ackerman. Wing was a member of the sounding team on the ship, launching weather balloons every three hours. This data was used in her honours project. She was able to identify the monsoon periods during the experiment and attempted to further the analysis of cirrus formation.