A comparison of cirrus cloud observations from the NASA ATTREX-3 field mission with simulations from the NCAR atmospheric CESM model (CAM5) coupled with an advanced cirrus cloud model (CARMA).

Cirrus clouds play an important role in the vertical transport of water vapor between the upper troposphere and lower stratosphere in the Tropical Tropopause Layer (TTL). Unfortunately, the physical limitations of observing the TTL and the model uncertainty surrounding cirrus clouds prevent a full understanding of the properties of cirrus and their role in water vapor transport. However, recently NASA’s ATTREX 3 field mission was undertaken to observe water vapor and cirrus properties in the TTL. The high altitude Global Hawk aircraft gathered a unique in-situ data set from the tropical Western Pacific. This region is known to be crucial for the upward motion of water vapor and chemical transport in the atmosphere, but has been observed infrequently. With the ATTREX data, we investigate the differences between in situ and anvil cirrus, and we assess the relative frequency of heterogeneous and homogenous ice nucleation. Alongside the observational data, we ran NCAR’s CESM model and coupled it to an advanced cirrus model (CARMA). The model was run at a 1x1 degree resolution along the aircraft’s flight track to simulate the observations. We compare the CAM5/CARMA simulations to the aircraft observations to investigate the effectiveness of the model in reproducing the aircraft data.