Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Imagery from the GOES-16 Advanced Baseline Imager contained banded features for several days in the spring of 2017. During the afternoon of 16 April 2017 over Durango, Mexico, non-stationary banded features were observed in imagery at 1.38 µm and 7.34 µm. Due to the influence of water vapor absorption, bright and dark bands were evident in 1.38 µm reflectances while co-located warm and cool bands were evident in 7.34 µm brightness temperatures. Based on observations, the following hypothesis is proposed: Thermally driven, banded, vertical circulations originating over complex terrain of western Durango transported water vapor upward. Pre-existing southwesterly flow, of the environment, subsequently advected the moist bands over the elevated terrain of the Sierra Madre Occidental in Durango. Due to the elevation of Durango, moist bands appeared relatively cool in imagery at 7.34 µm. Bright and dark bands were evident in imagery at 1.38 µm further north in the Sierra Madre Occidental (over the state of Chihuahua, Mexico) during the afternoon of 8 May 2017. Unlike the bands on 16 April 2017, broken linear segments of cumulus formed in the moist bands. Imagery of the split window difference, Tb(10.35)-Tb(12.3), also supported the development of cumulus in moist bands. Based on 8 May 2017 observations, the following hypothesis is proposed: Banded features in imagery at 1.38 µm over the state of Chihuahua were horizontal convective rolls. Dark bands at 1.38 µm represent the rising branch of the rolls and the location of the broken cumulus field. That is, the broken cumulus field represented the development of cloud streets within the rolls. One necessary condition to observe the banded structures at 1.38 µm is that the total precipitable water is less than about 0.5 cm.
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