Dry air aloft over the western Atlantic Ocean

January 23rd, 2019 |

GOES-16 Mid-level Water Vapor (6.9 µm) images, with plots of rawinsonde sites in yellow [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with rawinsonde sites plotted in yellow [click to play animation | MP4]

With a ridge of high pressure in place over the western Atlantic Ocean, GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) indicated the presence of dry air within the middle troposphere off the Southeast US coast on 23 January 2019.

GOES-16 “Red” Visible (0.64 µm) images showed that marine boundary layer stratocumulus clouds covered much of this region of the Atlantic — and due to minimal absorption by mid-tropospheric water vapor, these stratocumulus clouds were also very apparent in the corresponding GOES-16 Near-Infrared “Cirrus” (1.38 µm) images (below).

GOES-16 "Red" Visible (0.64 µm) and Near-Infrared "Cirrus" (1.37 µm) images, with plots of rawinsonde sites in yellow [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Cirrus” (1.38 µm) images, with rawinsonde sites plotted in yellow [click to play animation | MP4]

Terra MODIS Visible (0.65 µm) and Near-Infrared “Cirrus” (1.38 µm) images at 1513 UTC (below) also showed a clear signature of the stratocumulus clouds at 1.38 µm.

Terra MODIS Visible <em>(0.65 µm)</em> and Near-Infrared "Cirrus" <em>(1.38 µm)</em> images at 1513 UTC, with plots of rawinsonde sites in yellow [click to enlarge]

Terra MODIS Visible (0.65 µm) and Near-Infrared “Cirrus” (1.38 µm) images at 1513 UTC, with rawinsonde sites plotted in yellow [click to enlarge]

Cross sections of GFS90 model fields along Line I-I’ — oriented from Charleston, South Carolina to Bermuda — are shown below. Note the very dry air within the middle troposphere, with Specific Humidity values of less than 0.2 g/kg and Relative Humidity values less than 10% centered around the 500 hPa pressure level. In addition, the depth of the moist marine boundary layer was higher to the west at Charleston (2.6 km, at 746 hPa) than to the east at Bermuda (1.9 km, at 822 hPa).

Cross sections of GFS90 model fields along Line I-I', from Charleston, South Carolina to Bermuda [click to enlarge]

Cross sections of GFS90 model fields along Line I-I’, from Charleston, South Carolina to Bermuda [click to enlarge]