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Upper-troposphere and lower-stratosphere water vapor retrievals from the 1400...

Kindel, B. C., P. Pilewskie, K. S. Schmidt, T. Thornberry, A. Rollins, and T. Bui (2015), Upper-troposphere and lower-stratosphere water vapor retrievals from the 1400 and 1900 nm water vapor bands, Atmos. Meas. Tech., 8, 1147-1156, doi:10.5194/amt-8-1147-2015.

Measuring water vapor in the upper troposphere and lower stratosphere is difficult due to the low mixing ratios found there, typically only a few parts per million. Here we examine near-infrared spectra acquired with the So- lar Spectral Flux Radiometer (SSFR) during the first sci- ence phase of the NASA Airborne Tropical TRopopause EXperiment (ATTREX). From the 1400 and 1900nm ab- sorption bands we infer water vapor amounts in the trop- ical tropopause layer and adjacent regions between alti- tudes of 14 and 18km. We compare these measurements to solar transmittance spectra produced with the MODer- ate resolution atmospheric TRANsmission (MODTRAN) ra- diative transfer model, using in situ water vapor, temper- ature, and pressure profiles acquired concurrently with the SSFR spectra. Measured and modeled transmittance val- ues agree within 0.002, with some larger differences in the 1900nm band (up to 0.004). Integrated water vapor amounts along the absorption path lengths of 3 to 6 km varied from 1.26 × 10−4 to 4.59 × 10−4 g cm−2 . A 0.002 difference in absorptance at 1367 nm results in a 3.35 × 10−5 g cm−2 change of integrated water vapor amounts; 0.004 absorp- tance change at 1870 nm results in 5.50 × 10−5 g cm−2 of water vapor. These are 27 % (1367 nm) and 44 % (1870 nm) differences at the lowest measured value of water va- por (1.26×10−4gcm−2) and 7% (1367nm) and 12% (1870 nm) differences at the highest measured value of water vapor (4.59 × 10−4 g cm−2). A potential method for extend- ing this type of measurement from aircraft flight altitude to the top of the atmosphere is discussed.

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Atmospheric Dynamics and Precipitation Program (ADP)