Radar Remote sensing
Meteorological radars are one of the few ways how we can get information from what’s happening inside the cloud without actually flying inside of the cloud. Hence, with radars we are doing remote sensing instead of in-situ probing. In addition to the information about rainfall rate we all know from TV or Smartphone Apps, our research radars can tell us about where in the cloud we have ice particles, snowflakes, graupel, rain or drizzle drops. It can also tell us something about the amount of turbulence, wind shear, or vertical air motion inside the cloud. All these information is extremely valuable for improving numerical weather prediction models, which is of course the ultimate goal of all our activities.
Ice and snow cloud microphysics
Why do we need to understand ice and snow in clouds? Simply, because almost all precipitation falling over land is formed via the ice phase. After their nucleation, ice particle can grow by water vapor deposition, the can aggregate to larger snowflakes, liquid water droplets might freeze onto them forming rimed particles, and finally, the snowflakes melt at warmer temperatures into rain drops. All these processes or also called cloud microphysics, are key to understand in order to build numerical models which in the end are able to predict how much rain falls on the ground. But not only the precipitation is influenced by the ice part of clouds: The composition of ice clouds plays also a key role for the earth’s radiation budget which has implication for climate predictions.
What we measure with our radars is electromagnetic radiation reflected back from the cloud. In order to link these observed signatures to the actual physics inside the cloud, we need a radiative transfer model which is able to simulate the “theoretical radar image” given a certain composition of ice, snow, and rain. For our simulations in the microwave, we use a tool developed at IGMK called Passive and Active Radiative Transfer Operator (PAMTRA).
Scattering Properties of Ice and Snow Particles
How much of our radar signals is reflected back by a snowflake? How much is reflected by a dense graupel particle? How much is the radar signal absorbed by liquid water? All these questions are essential to answer before you can do a proper radiative transfer simulation. In our group we use models which can simulate various ice, snow, and rimed particles. In a certain sense, this model is our numerical laboratory to better understand the properties of ice particles. We use these simulated 3D objects to calculate their scattering properties needed for the radiative transfer.