By Adam Voiland
10 December 2014
(NASA) – About 4.5 million years ago, the Kashmir Valley was at the bottom of a large lake, encircled by a ring of rugged mountains. Much of the lake’s water has long since drained away through an outlet channel on the valley’s west side. However, evidence of the lake remains in the bowl-like shape and the clay and sand deposits on the valley floor.
The mountains surrounding Kashmir Valley now trap air a bit like they once trapped water. The high ridges can set up airflow patterns that concentrate smoke and other airborne pollutants near the valley floor, causing outbreaks of haze. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image of haze in the valley on December 5, 2014.
Haze is most likely to occur when warm, buoyant air moves over cooler, denser air—a situation meteorologists call a temperature inversion.Temperature inversions often develop on winter nights as the surface loses heat and chills the air immediately above. Mountain valleys often strengthen inversions because cold air from mountaintops tends to flow down slopes and push warmer air up from the floor in the process. Snow cover also increases the likelihood of an inversion because snow cools the air near the surface by reflecting much of the Sun’s energy rather than absorbing it. With a temperature inversion in place, air in the valley becomes stagnant; the warm air above it acts like a cap and prevents pollutants from dispersing.
Much of the haze visible in the image likely had its origins in charcoal production or the burning of biomass. Charcoal is widely used to heat homes in the Kashmir Valley in the winter and emits several types of polluting gases and aerosol particles into the atmosphere.
“You can tell this is pollution and not fog or mist by exploring the aerosol data available on Worldview,” explained Hiren Jethva, a NASA atmospheric scientist. “You can see that the Ozone Monitoring Instrument (OMI), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Atmospheric Infrared Sounder (AIRS) picked up a clear aerosol signal over the valley on December 5, as it did on several days in November as well.”