GXI 0.91 µm-based WVT Imagery of a Florida Sea Breeze

Figure 1: GeoXO/GXI water vapor transmittance (WVT).  At 20 UTC (last frame), the subtle darker shading near the coast shows the extent to which the sea breeze has moved inland.

Figure 2: Associated 20 UTC dewpoint from HRRR. Image from pivotalweather.com.

Today’s operations focused on convection moving across Florida with an associated sea breeze on the eastern coast. This provided an opportunity to see how this feature might appear in future GeoXO GXI imagery.  We looked at synthetic GXI imagery based on the 00 UTC HRRR output from the same day.

Figure 1 shows a short loop of synthetic water vapor transmittance (WVT) imagery.  WVT is the reflectance ratio of the 0.91 to 0.86 µm channels, and oftentimes better highlights areas of moisture than the 0.91 µm channel alone.  Darker areas (i.e. lower values) of WVT generally represent areas with higher total column water vapor.

At the end of the loop, as the sea breeze establishes itself inland (as demonstrated by the forecast dewpoints in Figure 2), a subtle area of darker shading in WVT is visible near the coast, delineating the extent to which the sea breeze has moved inland.

The dewpoint gradient across the sea breeze is only a few °F, which explains the subtleness of this feature.  Stronger sea breezes with larger moisture gradients will be much easier to identify than what is seen in this example (as regularly demonstrated in WVT from EUMETSAT’s Flexible Combined Imager (FCI) over Europe).  It is also noteworthy that the synthetic 5.15 µm did not identify the sea breeze, mostly due to the limited vertical extent of the sea breeze circulation.  WVT, by contrast, is sensitive to water vapor anywhere in the column.

-VortexTilting