Fixed-Grid Format Data flowing in AWIPS

June 19th, 2018 |

AWIPS imagery of GOES-16 Low-Level Water Vapor (7.34 µm) at 1527 and 1532 UTC on 19 June (Click to enlarge)

Until today, GOES-16 Data that flowed into AWIPS was remapped twice: First, from the observational perspective (that is, how the satellite views it) to a spherical fixed-grid projection that approximates the Earth, and then to a Lambert Conformal projection with (for infrared data) 2-km resolution over the Globe. That Lambert Conformal data was then shipped to AWIPS, where the data were again re-projected into the observational perspective desired by the meteorologist.

The 2-km resolution of the data shipped to AWIPS before today is applicable only at the sub-satellite point (nadir) for GOES-16. Thus, the second remap was suggesting better resolution than was warranted by the data. Additionally, the number of data points needed to be sent was very big.

At 1532 UTC on 19 June, the first fixed-grid format data were directly shipped to AWIPS; remapping to a Lambert Conformal projection is no longer done upstream of AWIPS. The toggle above shows the difference in the 7.34 µm “Low-Level” Infrared Water Vapor imagery over the coast of Oregon, near 46º N, 124º W (very far from the GOES-16 sub-satellite point at 0º N, 75.2º W), in the AWIPS CONUS projection.  At 1532 UTC, after the double remap is removed, the pixels are more distinct, and as expected they splay away from the sub-satellite point.

Removing a remapping in the data processing means that pixel-sized extremes — such as overshooting tops, or fires — and gradients will be better represented in the data.  Consider the Clean Window (10.3 µm) Infrared imagery below of strong convection over the Gulf of Mexico east of Texas.  Overshooting tops Brightness Temperatures are colder and the tops themselves more distinct after 1532 UTC than at 1527 UTC.

AWIPS imagery of GOES-16 Clean Window Infrared Data (10.3 µm) from 1347 to 1612 UTC on 19 June. The animation pauses on the last double-remapped image at 1527 UTC, and the first fixed-grid format image at 1532 UTC (Click to enlarge)


See also this blog postThis training also discusses the remapping.

Tornado in Luzerne County, Pennsylvania

June 14th, 2018 |

GOES-16 ABI Band 2 (Red Visible, 0.64 µm) over northeastern Pennsylvania. Luzerne County is outlined in Yellow, and Wilkes-Barre’s location is highlighted as a yellow box (Click to animate)

A confirmed tornado struck Wilkes-Barre in Luzerne County in northeastern Pennsylvania shortly after sunset on 13 June 2018 (at about 0215 UTC). Visible imagery, above, shows the line of thunderstorms approaching the region before sunset. This video, from Citizens Voice Reporter Nico Rossi, shows some of the damage.

NOAA/CIMSS ProbTor captured the tornadic cell very well (Click this link for a discussion that includes infrared satellite animations). Click here for real-time access to ProbTor.

1-minute Mesoscale Sector GOES-16 Band 13 (Clean Infrared Window, 10.3 µm) images with plots of SPC storm reports are shown below. The Wilkes-Barre PA tornado is plotted as a red T on the 0200 UTC image.

GOES-16 Band 13 (Clean Infrared Window, 10.3 µm) images, with SPC storm reports plotted in red [click to animate]

GOES-16 Band 13 (Clean Infrared Window, 10.3 µm) images, with SPC storm reports plotted in red [click to animate]

Below is a 1-km resolution Terra MODIS Band 31 (Infrared Window, 11.0 µm) image from shortly after the Luzerne County tornado, showing the line of convection that had developed in advance of a cold front. The 2 overlapping SPC storm reports (listed as damaging winds, with report times of 2008 and 2015 UTC) for the Wilkes-Barre event are in the center of the image. The minimum cloud-top infrared brightness temperature was -66ºC.

Terra MODIS Band 31 (Infrared Window, 11.0 µm) image, with plots of cumulative SPC storm reports and the 03 UTC position of the surface cold front [click to enlarge]

Terra MODIS Band 31 (Infrared Window, 11.0 µm) image, with plots of cumulative SPC storm reports and the 03 UTC position of the surface cold front [click to enlarge]

Why Mesoscale Sectors matter: Tropical Storm Aletta

June 6th, 2018 |

GOES-16 Visible (0.64 µm) Imagery, 1422-1741 UTC on 6 June 2018 (Click to animate)

The first Tropical Storm, Aletta, of the eastern Pacific Ocean basin has been named. One-minute imagery from a moveable Mesoscale Sector, above as an animated gif (or here as an mp4), shows a distinct low-or mid-level circulation center moving out from under higher clouds in the northeast quadrant of the storm at about 1621 UTC, being even more obvious at 1636 UTC.

The GOES-16 CONUS Sector scans at 5-minute intervals. The southern boundary of the CONUS sector (15º N Latitude), however, bisects this tropical storm, as shown at this link, and is therefore unhelpful for center diagnostics. Full Disk imagery captures the storm evolution at a 15-minute time step that is too coarse to provide a smooth animation. (Just two years ago, the time resolution for this storm formation would have been every 3 hours, as that was the time cadence for a Full Disk from GOES-13! GOES-16 really is life-changing for those who view satellite animations.)

The Split Window Difference over Iowa

June 5th, 2018 |

GOES-16 ABI Split Window Difference (10.3 µm – 12.3 µm) at 1402 UTC on 5 June 2018 (Click to enlarge)

The Split Window Difference field (SWD, the 10.3 µm brightness temperature minus the 12.3 µm brightness temperature) can be used to identify regions of moisture and dust in the atmosphere.  (Click here for a previous blog post).  On 5 June 2018, the SWD showed a strong gradient over the upper Midwest, with large values over Iowa and relatively smaller values to the northeast over Wisconsin (and to the south over Missouri). Is this showing a moisture gradient between Iowa and Wisconsin? Do you trust its placement? Given that convection will frequently fire along the gradient of a field (HWT Link; Old HWT link), it’s important to trust the placement of the gradient.

The toggle below shows both the SWD and the (clear sky only) Baseline Derived Stability Lifted Index.  The Lifted Index shows negative values over the southern Plains, and also a lobe of instability stretching WNW-ESE from southwestern Minnesota to Chicago.  If you look carefully, you will note that the axis of instability in the Lifted Index is offset from the Split Window Difference field.  Why?

GOES-16 ABI Baseline Derived Stability Index Lifted Index and GOES-16 Split Window Difference (10.3 µm – 12.3 µm) at 1402 UTC on 5 June 2018 (Click to enlarge)

The toggles below show the Split Window Difference field and the Rapid Refresh Model estimates of moisture in the lowest 3 km of the atmosphere, followed by the Split Window Difference toggled with the Baseline Land Surface Temperature field. The maximum in moisture is along the northern edge of the Split Window Difference field, and aligns well with the Lifted Index (Toggle between those two is here).

The Split Window Difference better matches the Land Surface Temperature Baseline product, and that reinforces an important caveat in the use of the SWD to detect moisture: SWD is greatly influenced by the skin temperature. Gradients in surface temperature and gradients in moisture both will affect the Split Window Difference. Make sure you understand the underlying cause of the gradient in the Split Window Difference field.

Toggle between the GOES-16 ABI Split Window Difference (10.3 µm – 12.3 µm) and Mean 0-3km AGL Dewpoint from the Rapid Refresh Model, 1402 UTC on 5 June (Click to enlarge)

GOES-16 ABI Split Window Difference (10.3 µm – 12.3 µm) and Land Surface Temperature Baseline Product, 1402 UTC on 5 June 2018 (Click to enlarge)

By 2002 UTC on 5 June, the GOES-16 Lifted Index fields and the SWD more closely align, in part because the axis of moisture has shifted southward. See the toggle below.

GOES-16 ABI Baseline Lifted Index, Split Window Difference (10.3 µm – 12.3 µm) and 0-3 km AGL Rapid Refresh Dewpoint, 2002 UTC on 5 June 2018 (Click to enlarge)