Radiative flux measurements during the Airborne Tropical Tropopause Experiment (ATTREX) Guam Deployment.

Abstract:

The Airborne Tropical Tropopause Experiment was a field program utilizing the NASA Global Hawk aircraft, to make extensive measurements of tropical tropopause layer (TTL) over the Pacific Ocean. In February and March of 2014, the NASA Global Hawk was deployed to Guam and flew six long duration science flights. The aircraft was outfitted with a suite of instruments to study the composition of the TTL. Measurements included: water vapor amount, cloud particle size and shape, various gaseous species (e.g. CO, CH₄, CO₂, O₃), and radiation measurements. The radiation measurements were comprised of the Solar Spectral Flux Radiometer (SSFR) that made spectrally resolved measurements of upwelling and downwelling solar irradiance from 350 to 2200 nm and thermal broadband (4μm to 42 μm) upwelling and downwelling irradiance. Once airborne, the Global Hawk made numerous vertical profiles (14 – 18 km) through the TTL. In this work we present results of combined solar spectral irradiance and broadband thermal irradiance measurements. Solar spectral measurements are correlated, wavelength-by-wavelength, with broadband thermal measurements. The radiative impact in the TTL of water vapor and cirrus clouds are examined both in the solar and thermal wavelengths from both upwelling and downwelling irradiances. The spectral measurements are used in an attempt to attribute physical mechanisms to the thermal (spectrally integrated) measurements. Measurements of heating rates are also presented, highlighting the difficultly in obtaining reliable results from aircraft measurements.