Balloon Measurements of Microphysical and Optical Properties of Tropopause Cirrus Clouds during the BATAL Campaign

Abstract:

In situ measurements of cirrus clouds, in-particular subvisible cirrus clouds near the tropopause over the Asian Summer Monsoon (ASM) region are scarce. Here, we present the first balloon-borne measurements of the microphysical and optical properties of a tropopause cirrus cloud layer obtained during the Balloon measurement campaigns of the Asian Tropopause Aerosol Layer (BATAL) over Hyderabad, India. On 23 August 2017, simultaneous measurements from a backscatter sonde (COBALD), a radiosonde and an optical particle counter (Boulder Counter) reveal the presence of a subvisible cirrus cloud layer located at the cold-point tropopause (CPT) with temperature near -86.4° C. Near coincident measurements from the Cloud Aerosol Transport System (CATS) lidar onboard the International Space Station (ISS) suggest that this layer extends over more than 500 km along its orbit track. A log-normal size distribution is used to fit the Boulder Counter data and derive the microphysical properties of this layer. Ice-crystals in this layer are smaller than 50 μm with a mean concentration of about 47.5 L^-1. The ice-water content estimated from our measurements is about 0.17 mg/m³. Layer mean lidar ratio (30.9 sr) is also estimated using independent measurements of backscatter and extinction coefficients from COBALD and Boulder Counter measurements, respectively. The formation mechanism responsible for this tropopause cirrus is investigated using three dimensional back trajectories, observations from space-borne lidars (CALIOP/CALIPSO and CATS/ISS) along with cloud-top brightness temperature images from Himawari-8 satellite and temperature from GPS radio occultation measurements. These combined data suggest that the formation of the tropopause cirrus is likely influenced by a Category-3 Typhoon, Hato which hit Macau and Hong Kong on 23 August 2017.