California fires: a “smoke signal” in the water vapor imagery?

October 23rd, 2007 |

AWIPS GOES 4-panel (Animated GIF)

The large wildfires continued to burn across parts of southern California on 23 October 2007. AWIPS images of the GOES-11 imager visible channel (upper left panel), 6.7 µm water vapor channel (upper right panel), 10.7 µm IR channel (lower left panel), and the GOES-11 Sounder 4.0 µm IR channel (lower right panel) reveal an interesting signature of the smoke pall that had been transported westward out over the Pacific Ocean — on the water vapor channel! Since H2O is a byproduct of combustion, the water vapor content of the aged smoke pall is somewhat elevated compared to the rather dry ambient atmosphere over the eastern Pacific Ocean; this allows a subtle signature of the smoke feature to appear on the GOES imager water vapor channel. There is no signal on either of the IR channel images (bottom 2 panels) since smoke is transparent to thermal radiation at those wavelengths.

MODIS RGB images (Animated GIF)

A comparison of two 500-meter resolution Terra MODIS red/green/blue (RGB) image composites (above) shows a closer view at the fires in the Los Angeles and San Diego region. The MODIS Channel 01/04/03 RGB image approximates the “true color” images that appear on the SSEC MODIS Direct Broadcast site. The MODIS Channel 07/02/01 RGB image takes advantage of the temperature sensitivity of the “near-IR” Channel 07 (2.1 µm) to make the hottest active fires appear with a pink to red enhancement (the red pixels over water are due to sun glint). The large dark burn scar resulting from the 70,000-acre fire just southwest of San Diego (station identifier KSAN) is just starting to become evident on the 07/02/01 RGB image, even through the thick smoke plume seen on the 04/03/01 RGB image.

IDEA trajectory forecast

The IDEA MODIS aerosol optical depth (AOD) trajectory forecast (above) suggested that some of the thick smoke could get recirculated back over portions of northern California within the 48-hour forecast period; however, the trajectory trend indicated that these aerosols might remain just above the boundary layer, which would limit their impact on surface air quality in the San Francisco region. The National Weather Service also provides a 1-hour average vertical smoke integration product as part of their Air Quality Forecast Guidance.

Rope Cloud in the Gulf of Mexico

October 23rd, 2007 |

ropemovie.gif

Rope clouds are elongated lines of cumuliform clouds that develop at the leading edge of an advancing cold front. They are most commonly seen over the ocean, where friction and topography effects that might disrupt the development of a line are minimal. For the example seen today, a RUC temperature analysis over the Gulf to the east of the line show temperatures in the 80s (Fahrenheit) at 1500 UTC; RUC analysis temperatures drop quickly into the 60s and 70s behind the line, even over the warm waters of the Gulf.

Satellites other than geostationary viewed this line. Click here to view the rope cloud as seen by NOAA-17, and click here for the MODIS imagery. Both polar orbiters give higher spatial resolution views — at the cost of lower temporal resolution.