A River of Haze

As is often the case in the winter, a thick river of haze hovered over the Indo-Gangetic Plain in January 2013, casting a gray pall over northern India and Bangladesh. On January 10, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of haze hugging the Himalayas and spilling out into the Ganges delta and Bengal Sea.

The haze likely resulted from a combination of urban and industrial pollution, agricultural fires, and a regional meteorological phenomenon known as a temperature inversion. Usually the air higher in the atmosphere is cooler than the air near the surface, a situation that allows warm air to rise and disperse pollutants. However, cold air often settles over northern India in the winter, trapping warmer air—and pollution—close to the surface, where it has the greatest impact on human health.

Air quality has emerged as a significant problem for India and Bangladesh in the past decade. A study conducted by Tel Aviv University researchers and published in the American Journal of Climate Change found that levels of air pollution in large Indian cities increased at some of the fastest rates in the world between 2002 and 2010—faster even than rapidly-growing Chinese cities.

Many Indian cities recorded double-digit increases in pollution over the study period. Calcutta, the third-most populous city in India, saw an 11.5 percent increase in pollution; Bangalore (not shown in the image) had the largest increase of any Indian city: 34 percent. The research was based on information collected by MODIS and by the Multi-angle Imaging SpectroRadiometer (MISR) on NASA’s Terra satellite.

• References

• Pinhas, A. (2012, Nov.) AOD Trends over Megacities Based on Space Monitoring Using MODIS and MISR (PDF). American Journal of Climate Change. Accessed Jan. 11, 2013.
• Hindustan Times (2012, Nov. 30) India Tops China in Air Pollution Level Increase. Accessed Jan. 11, 2013.
• Time (2013, Jan. 8) India’s Air Pollution: Is It Worse Than China’s? Accessed Jan. 11, 2013.

1. Further Reading

2. NASA (2010, Sept.15) NASA Data Track Seasonal Pollution Changes Over India. Accessed Jan. 11, 2013.
3. New York Times (2012, Feb. 1) India’s Air the World’s Unhealthiest, Study Says. Accessed Jan. 11, 2013.

NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response. Caption by Adam Voiland.

Instrument: 

Aqua - MODIS - NASA

Dense Fog over the Missouri and Mississippi Rivers

The day before Thanksgiving is one of the busiest travel days of the year in the United States. But on November 21, 2012, weather posed a challenge for people flying in and out of St. Louis, Missouri. It also posed a challenge for drivers making their morning commutes. Thick fog descended on the city overnight on November 20–21, and on the morning of November 21, visibility was as low as one-sixteenth of a mile (0.1 kilometers), according to news reports.

Fog lingered over the region when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image at 10:45 a.m. local time (16:45 UTC) on November 21. Fog filled the Mississippi River Valley as well as the valleys of the Missouri River and many of its tributaries. Fog extended from Jefferson City in the northwest to Cape Girardeau in the southeast. Situated at the confluence of the Missouri and Mississippi Rivers, St. Louis was engulfed by low clouds.

Fog is simply clouds that have formed at ground level. Like all clouds, fog forms when the local air reaches its dew point—the temperature at which water vapor condenses into tiny droplets. In the autumn, the moisture content of the atmosphere remains relatively high, but nights are cool. Overnight, the ground tends to cool faster than the atmosphere, and air in contact with a cooling, sloped surface will slide down and settle in the valley floor. Because autumn brings longer nights, fog has more time to form and is a fairly common occurrence.

1. References

2. AccuWeather. (2012, October 16) Mountain valley fog: What causes it? Accessed November 26, 2012.
3. Blume, B. (2012, November 21) Dense fog settles over St. Louis, cutting visibility to near zero. CBS St. Louis. Accessed November 26, 2012.
4. Department of Atmospheric Sciences. Observed dew point temperature. University of Illinois at Urbana-Champaign.
5. Hudson, K. (2012, November 21) Fog affecting Lambert flights on busy Thanksgiving travel day.
6. KMOV. (2012, November 21) Dense fog blankets the News 4 viewing area. Accessed November 26, 2012.

NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC. Caption by Michon Scott.

Instrument: 

Terra - MODIS

Fog in Argentina’s Lake District

On the morning of March 29, 1987, the Thematic Mapper on the Landsat 5 satellite captured this scene of fog lingering in valley bottoms of Argentina’s Lake District.
The Lake District, a popular destination for travelers due to its dramatic alpine views and numerous glacial lakes, is located in the eastern foothills of the Andes, near the Chilean border. A number of large lakes—including Villarino, Hermoso, and Meliquina—lie below the fog, out of view. The bright green and pink blotch on the upper left of the image is missing data. The lower image, acquired by Landsat 5 on February 15, 2001, shows the same area on a fogless day.
Clouds are fields of water droplets or ice crystals suspended in the air. Fog is simply a cloud in contact with the ground. Like all clouds, fog forms when air is cooled enough that the water vapor within reaches its dew point, the temperature at which vapor condenses into liquid droplets.
Fog forms in a number of different meteorological circumstances, but the fog shown above is most likely radiation fog. This common type develops on clear, calm nights as Earth’s surface—and the air immediately above—cools overnight. Radiation fog is most likely to form when there is a layer of cool air near the surface and a layer of drier air above it. Since air near the surface is usually warmer than the air above it, reversals like this are known as temperature inversions.
In the case of the image above, the steep valleys facilitated the inversion. When air along the upper slopes of mountains begins to cool after sunset, it becomes dense and heavy, draining down the mountain slopes toward the valley floors. This cool air piles up in the lowest part of a valley, and it is there that fog is most likely to form.
“The fog boundaries are so sharp because, more than likely, they correspond to a particular altitude in the terrain, which corresponds to the height of the base of the temperature inversion,“ explained Patrick Minnis, a senior research scientist at NASA’s Langley Research Center.
Radiation fog can occur in the absence of underlying water, but in this case the lakes likely contributed by increasing the humidity near the surface. For the same reason, radiation fog tends to form in swampy areas or after a heavy rainfalls or snowmelts. It can be quite thick, posing a threat to boaters and motorists in the morning. However, it is usually short-lived. When the sun returns in the morning, the air near the surface heats up and fog usually burns off in a matter of hours.
“That texture you’re seeing in the fog is caused by convective processes that are starting to break it up,” noted Minnis.

1. Further Reading

2. Earth Observatory. (2010, February 23) Valley fog in British Columbia. Accessed November 16, 2012.
3. Earth Science Picture of the Day. (2009, July 1). Radiation fog in Topanga Canyon. Accessed November 16, 2012.
4. National Geographic. (n.d.) Fog. Accessed November 16, 2012.
5. NOAA. (n.d.) Fog types. Accessed November 16, 2012.
6. Pilar, C. (1991, August). The occurrence of fog in Chile. Journal of Applied Meteorology

NASA Earth Observatory images by Jesse Allen and Robert Simmon, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland. There were no winners this month. Stuart, David P., and Michael Osborn were some of the first puzzler players to get close.

Instrument: 

Landsat 5 - TM - NASA

Fog over parts of Europe

Illustration of the changing low-cloud and fog conditions (pale colours) over central and eastern Europe at hourly intervals over two days. The heavy fog has caused severe disruptions at airports across Europe.

Source: Meteosat-9 24-hour Cloud Microphysical RGB (22/10/12 00.00 - 23/10/12 01.00)

Met Office issues severe weather warning as thick fog leads to more than 120 cancelled flights at Heathrow

Image: An Austrian Airlines Fokker 100 plane is grounded at the Chopin International Airport in Warsaw this morning because of the thick fog

Heavy fog blanketed the country today causing severe disruptions at airports across England and Europe.

More than 120 inbound and outbound flights have been cancelled at Heathrow - the country's busiest airport - with every inbound flight and many outbound flights delayed as pilots battle with visibility problems.

But as the thick fog continues to hang in the air, more flights are likely to be cancelled this evening and tomorrow.

Read more: http://www.dailymail.co.uk/news/article-2221343/UK-Weather-Met-Office-issues-severe-weather-warning-fog-leads-120-cancelled-flights.html#ixzz2A5j2TImZ

FOG/MIST - SA Weather Satellite Image: 8 September 2012 05h00 SAST

Image: Eumetsat (Click on image for larger view.)

TrafficSA and SAWDOS Observers reported heavy fog this morning in the following areas:

wolfzwe @SAWDOS1 Heavy, thick mist over Alberton, Jhb south. Lights on, keep the distance on the road. Keep lookout for cyclists pedestrians.

TrafficSA Cape Town - N7 Route, poor visibility due to #fog (very thick) between Kalbaskraal and Moorreesburg - headlights ON, proceed with care

TrafficSA JHB / Free State - N3 Route, Mist affecting visibility between Heidelberg and Warden

TrafficSA JHB - N3 Route, Mist affecting visibility between Vosloorus and Johannesburg - headlights ON - drive with care

TrafficSA Pretoria - Thick and Heavy #Fog between Soshanguve and Pretoria - reduce speeds and proceed with caution

The fog is clearly visible on the above satellite image.

HEADLIGHTS ON AND DRIVE VERY CAREFUL IN THESE CONDITIONS

- SAWDOS

Current misty conditions in the Durban area

Image supplied by Jan ten Hoorn Boer

Fog still causing misery at Auckland Airport

Planes stranded by fog at the domestic terminal Auckland Airport. Photo / Sarah Ivey

Fog is continuing to force cancellations and delays to flights out of Auckland Airport this morning.

At 11:30am, the Auckland Airport website showed 28 domestic arrivals and 25 departures had been cancelled.

Another 14 domestic departures and 21 arrivals had been delayed or "delayed indefinitely".

An airport spokeswoman said five international flights had also been delayed due to the fog.

It was showing no sign of clearing, she said.

Air New Zealand spokeswoman Tracy Sneaton said it was not yet known how many passengers had been affected.

MetService meteorologist Daniel Corbett says visibility is about 800 metres this morning and is likely to improve between 10am and midday.

"Just about sunrise, fog tends to get a bit worse and then it slowly improves as the sun melts away the layer of fog on the ground,'' he said.

Ms Sneaton said all of Air New Zealand's domestic jets were operating to schedule but regional services had been put on hold.

Ms Sneaton said a flight from Rarotonga had been diverted to Wellington, where aircraft had refuelled and would be heading back to Auckland Airport.

Passengers are being told to check arrivals and departures information on the airport website.

"Very hard to predict fog, as soon as the low visibility has lifted we will be advised,'' airport spokesman Richard Llewellyn said.

- APNZ

Fog this morning over the bay in Mossel Bay (4 June 2012 07h20 SAST)

Images: SAWDOS (Click on image for larger view.)

Mist along the West Coast (8 May 2012 15h50 SAST)

Image: NOAA18 (Ben Engelbrecht, Dundee) Click on image for larger view.

Crayfish boats on the West Coast were caught unawares late yesterday afternoon when a thick mist moved in extremely fast all the way up the coast. The above image clearly reflect the mist cloud along the West Coast. (Circled in yellow)

Mist causes chaos on West Coast

Crayfish boats on the West Coast were caught unawares late yesterday afternoon when a thick mist moved in extremely fast all the way up the coast.

Mykonos Sea Rescue were put on standby as the weather moved in and eight crayfish boats were caught out at sea in the mist.

According to Darius Van Niekerk, Station Commander at Mykonos the first call was for a crayfish boat off Doringbaai lost in thick mist. After that the calls were received in quick succession for four crayfish boats in the mist at Hondeklipbaai and a bigger crayfish boat with two smaller “bakkies” (small row boats) off Lamberts Bay.

The boat at Doringbaai saw a searchlight being shone out to sea by the Police and was able to get safely back to land and the four boats, which were together off Hondeklipbaai, were brought back safely by a private vessel with navigation equipment on board.

The final group of three boats off Muisbosskerm ( Lamberts Bay) waited for the mist to lift. All were safely home by 22h00.

“Because people on shore knew where the boats were they could be helped to get safely back to shore,” said Darius.

- NSRI