Advances in Aircraft Measurements of Clouds and Precipitation in China

Abstract

Aircraft measurement is an important way in observing the phase, distribution and conversion of clouds and precipitation particles in clouds. The data of aircraft measurements are the foundation for clarifying cloud microphysical structure and precipitation formation mechanism, as well as the parameterization of cloud physical processes in numerical model. The main achievements in technology, instrument and research of aircraft measurements in China are summarized.The aircraft measurements of clouds and precipitation started in the 1960s with an airborne aluminum foil sampler in China, and then size distribution, number concentration and images were acquired with a microscope. Early in the 1980s, the particle measuring system (PMS) was firstly imported and used. After 60 years of development, China has made important advances and achievements in aircraft measurement platform, airborne measurement technology and research in cloud microphysical processes and precipitation formation mechanisms. Some important research results are summarized as follows. First, the properties of atmospheric aerosols and conversion into cloud condensation nuclei (CCN) are found to be closely related with atmospheric stratification, aerosol origins and secondary aerosol formation. The atmospheric inversion plays a critical role in the accumulation of aerosols in low levels. The secondary aerosols formed in air pollution events have low conversion rate as CCN since the aerosols are fine particles and need higher supersatuation for nucleation, and the high-level large-size dust aerosols have higher conversion rate. Second, the microphysical properties of stratiform clouds and stratiform clouds with embedded convection are closely associated not only with cloud-top temperature, water vapor content and cloud thickness, but also with the location in the high-level trough and cold/warm frontal system. The embedded convection region has more supercooled water and the riming process is critical, and the precipitation formation follows the seeder-feeder mechanism. In the thinner stratiform region, the supercooled water content is less, deposition and aggregation are dominant, and therefore the precipitation formation cannot follow the seeder-feeder mechanism. However, when clouds grow moister and thicker, the deposition, aggregation, and riming processes are dominant. Third, the microphysical formation mechanism in winter snow events in northern China are mainly due to deposition and aggregation processes. Only under the condition with plentiful water vapor and deeper cloud, the riming process is important. Aircraft measurements are important in verifying the microphysical processes in numerical model, however, the current studies are only limited in direct comparisons. The improvements of microphysical processes in a model through parameterization of aircraft measurements are very limited. In addition, aircraft measurements in convective clouds, warm-rain microphysics and applications in cloud seeding effectiveness evaluation and verification in remote sensing observational data are still insufficient.

Keywords

• clouds and precipitation
• aircraft measurements
• precipitation formation mechanism