MODIS RGB Dust Observations in New Mexico and Texas

The SPoRT MODIS RGB Dust product has just been operational for a couple of weeks at the Albuquerque WFO and already it’s showing strong potential utility for operational forecasters.  On the afternoon of April 14th, the product showed the presence of several distinct dust plumes blowing off the Sierra Madre in the Chihuahuan State of Mexico.  In the RGB Dust product, the dust plumes are represented by the magenta streaks stretching from northern Chihuahuan State into west Texas and southern New Mexico.  One particularly large swath of dust can be seen across El Paso, TX and Alamogordo, NM.

Figure 1. SPoRT MODIS RGB Dust Product valid 2033 UTC April 14th 2012

In the dust product, the red color is reserved for the 12.0-10.8 um band, which is related to optical thickness.  With a relatively large contribution from this difference channel, the difference is positive, meaning that more of the 12 um radiation passes through.  In the magenta color though, there is a fair amount of blue coloring, which indicates a relatively warm surface.  During the daytime, the height of the dust is difficult to determine because of contributions of the warm surface through the dust.  So, the dust will typically appear as a magenta or pink color.  However, observations will indicate whether or not the dust is at the surface.  This image made available from Brian Guyer at the Albuquerque NWS office shows a close-up of part of the area in question.  Notice the dust observation at the El Paso, TX airport in the far lower left corner of the image.

Figure 2. SPoRT MODIS RGB Dust image overlain with observations valid at 2033/2100 UTC April 14th 2012

Also interesting was the evolution of the dust in the dry airmass behind the dryline across eastern New Mexico and into west Texas.  In figure 3 below, notice the pink areas stretching from the Midland (MAF) County Warning Forecast Area (CWFA) through the Lubbock (LUB) CWFA and into the Amarillo (AMA) and Dodge City (DDC) CWFAs.  The deep red clouds cutting across the eastern portions of the Lubbock, Amarillo and Dodge City CWFAs, and the western Norman CWFA are representative of cold clouds and deep convection.  These were the thunderstorms that developed along the dryline late that afternoon into the evening.

Figure 3. SPoRT MODIS RGB Dust product valid 0417 UTC April 15th 2012

A zoomed in image, again courtesy of Brian Guyer of the Albuquerque office shows observations with haze and dust, particularly in portions of west Texas.  Notice the 79/61 temp/dewpoint at KBPG in the far lower right portion of the image, while an observation of 74/21 exists just a couple of counties to the northwest at KGNC.  An observation of dust can be seen at Lubbock (KLBB).

Figure 4. SPoRT MODIS RGB Dust image overlain with observations valid 0400/0417 UTC April 15th 2012

Probably more on these images will follow next week.  If you have any interesting comments or notice any other features, please feel free to point them out.  Another item of note, notice the stark contrast between colors in figures 1 and 2 across west Texas.  This product seems to detect the dryline boundary quite well.

2 thoughts on “MODIS RGB Dust Observations in New Mexico and Texas

  1. These images are “heatmaps” in a sense, in that they depict wavelengths within the IR spectrum. Specific wavelengths or wavelength differences are assigned to red (R), green (G), or blue (B) color contributions. In this particular product, red color contribution corresponds to the 12.0-10.8 µm wavelength, or channel, difference. Where there are thick clouds or dust, the difference between these two channels will be larger, as more radiation at 12 µm passes through these phenomena than at 10.8 µm. Green color contribution corresponds to the 10.8-8.7 µm difference, and blue color corresponds to the 10.8 µm channel. Notice the area of thick convective clouds (figures 3 and 4) extending from the TX panhandle region into south central KS. These clouds appear as nearly pure red, indicating most of the color contribution in this area is from the 12.0-10.8 µm channel difference. Little contribution exists from the green, indicating the presence of ice in the clouds. There will likewise be little contribution from the 10.8 µm channel (blue color), since the tops of the deep convective clouds are relatively cold. However, notice the magenta colors just to the west in these figures. The magenta color indicates contributions from both the blue and red. Here, the dust is thick, but not as thick as the clouds or as absorptive of the 10.8 µm radiation. So, more of the blue, represented by the 10.8 µm, bleeds through the dust, and we are left with the magenta color.

    What is this used for? The Albuquerque office, which is a collaborator of SPoRT, can use these products to help locate and better forecast movement of dust plumes to put in their forecasts. Since dust can be an inhibitor to visibility, this type of imagery may also be used to help forecast obscurations at airports in terminal aerodrome forecasts (TAFs). However, if ABQ is following, I’ll let them expand some more if they wish.

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