Cyclone Mahasen, Gravity Waves, and Imminent Humanitarian Disaster

Projected path of Cyclone Mahasen as of May 14, 2013

Bearing in mind that hurricane, cyclone and typhoon are all words for big cyclonic storms, Cyclone Mahasen bearing down on Bangladesh, Myanmar (formely Burma) and possibly northeast India depending on its trajectory. The low-lying areas poses a flooding threat to millions of people, some estimates being as many as 8.2 million. Particularly at risk are about 140,000 living in makeshift quarters in low-lying camps. The cyclone has weakened to a Category 1 tropical storm rather than a cyclone, but the large extent of low-lying areas in Bangladesh poses a major problem with wind, rain (up to 500 mm), tidal surge and waves in the forecast.
     Mahasen is being pushed to the northeast by a trough of low pressure. There are heavy thunderstorms, largely out over water around the southeastern coast of India. MODIS images on NASA's Terra satellite showed that (as of May 14) it was a tightly wound, compact storm with strong convection around the storm center. it is moving about 8 mph to the northeast (as of May 14). Sea surface temperatures in the Bay of Bengal are near 84-86 F, warm enough to support the tropical cyclone, and vertical wind shear is minimal, allowing the storm to potentially strengthen.
     NASA has released an image (lower right) on which someone has sketched atmosppheric gravity waves traveling out from the center of the storm. This suggests that the core of Mahasen extends up into the stratosphere. Gravity waves transfer the momentum from the stratosphere back down into the troposphere as the system seeks to regain density equilibrium.

Gravity waves (marked with circle and arcs) from
Cyclone Mahasen NASA image

       This storm illustrates a potentially tragic intersection of earth processes and human affairs. A stateless Muslim minority, the Rohingya, was created when sectrian violence erupted between Buddhists and Muslims last year. The Rohingya suffered during decades of military rule in Myanmar, and they have been forced to live in camps in the low lying areas of these countries. The Rohingya are reluctant to leave the camps because they distrust the security forces involved, say United Nations spokesmen. Already a boat ferrying people from one camp in Rakhine (a state in Myanmar) to safer areas has capsized with 58 people still missing from the accident. Authorities are well organized for the storm preparation, having been subjected to repeated cyclones. In 1970 Cyclone Bhola killed an estimated 400,000 people. Landfall is expected Thursday or Friday morning near Chittagong, Bangladesh, which may spare the restive state of Rakhine from its full impact.

Cyclone over Lake Michigan: Flying into O'Hare is always interesting!

Cyclone over Lake Michigan on September 26, 2011
Image from GOES NASA

Last Monday I was returning from the west coast, my flight delayed nearly an hour and a half by "weather in Chicago."  When we finally did depart and get over to the Chicago area four hours later, the landing was a prolonged bumpy ride, as was the puddle jumper down to Urbana. Described by The Capital Weather Gang as a "lumbering, sprawling cyclone," this weather system dominated the mid-West for three days from September 25-27.

This storm is a classic example of the mid-latitude cyclones that dominate the weather in the U.S. Air circulates counterclockwise around a low pressure core (in the Northern Hemisphere). Warm air pushing north and cold air pushing south get wrapped in bands around the center of the cyclone. Air in the low-pressure center rises to form towering clouds, and the comma-shaped tail consists of warm moist air (clouds) and colder dry air (clear areas). In the mid-west, cold air eventually "wins out and wraps completely around a storm," forming a so-called "cold core" storm.  It gets cut off from the jet stream and so, in this case, stalled near Chicago.  The Earth Observatory WWW site which featured this storm has a great animation of the storm from GEOS, here.

These cyclones develop when a trough in the jet stream interacts with a surface frontal zone. The essential low-ressure system forms if there is wind shear (winds increasing with height in the atmosphere) and convection (thermal instability). Three factors lead to formation of the low pressure at the surface: diverging airflow at high altitudes; warm, moist air flowing in at low and mid-levels; and latent heat release.  The storm typically has four stages, all of which can be seen in the video above.  First, a leaf cloud forms on the east side of the trough, a zone of deep and thick clouds. Within the leaf cloud, air is rotating and as the system develops, the clouds develop into a comma shape, which takes on various forms depending on the eastward motion. As the storm develops, the low-pressure circulation gets cut off from the jet stream and without the momentum from the jet stream, the system loses its ability to deepen.  The cold front overtakes the warm front and the system becomes "occluded." After this, the storm weakens as the upper-level winds tear it apart. The comma head may lag behind and continue to rotate, a phenomenon seen on the video above. The discussion and schematics here are very helpful in understanding the process of "cyclogenesis."

Cyclone Yasi bearing down on Australia--TAKE CARE AUSSIE FRIENDS!

Cyclones Anthony (lower left) and Yasi (center)
U.S. Geostationary satellite

Comments added 02/02/2011: The core of Yasi is expected to take four hours to pass over an area, a measure of the size of this cyclone. It will last 3 days, and still be a category 1 storm (winds up to 125 km/hour) when it is 900 km inland. More than 89,000 people in north Queensland have lost power. The storm tide in Townsville is reaching the 3 meter mark, with expected surges of 7 m. For a discussion of the impact of this to Australia's economy, see Businessweek.com. Here is a link to a good NASA Earth Observatory image.

Cyclone Yasi is now a larger-then- Katrina-sized storm bearing down on Queensland's tropical coast, expected to make landfall in the early hours of Thursday a.m. (Australia time; Brisbane is 16 hours ahead me at US Central Daylight Time). It follows on the heels of Cyclone Anthony which left Queensland drenched not long ago. For a set of superpositions like the one below showing Yasi compared to Europe or Asia, go here.
        Yasi is currently over the warm waters of the Coral Sea. These provide energy and water into the cyclone just as the warm waters of the Gulf of Mexico provided fuel for Hurricane Katrina. Here's a good tutorial on tropical cyclones in the Atlantic--just reverse directions for the southern hemisphere!
       Yasi was upgraded to a Category 5 storm at 5:00 am AEDT.  It was about 650 km E-NE of Cairns and 650 km NE of Townsville. It is moving W-SW at 30 km/h. Coastal residents between Port Douglas and Townsville are warned of an "extremely dangerous" storm tide, with flooding inland.  This storm unfortunately is only weeks after the last episode of severe flooding in Queensland. Gusts reaching 280 km/h are expected in some regions in the evening. Unfortunately, the peak of the storm will hit Cairns in the dark, about 10:00 in the evening. The Australian Defence Force has evacuated hundreds of patients from two hospitals in Cairns.

Cyclone Yasi superposed on the USA
http://www.news.com.au/breaking-news/floodrelief
/how-cyclone-yasi-compares-around-the-world/story-fn7ik2te-1225998762870

Trivia: 280 km/h is 77 m/s.  The speed of sound in air is 340 m/s.   These winds would have a Mach number of 0.23, not trivial!!

Projected path of Yasi

Unfortunately, Yasi is going right over Australia's famed Great Barrier Reef.  The projections are for hurricane force winds and sea swells greater than 6 meters.  Coral reefs growing in cyclone areas suffer periodic damage from the waves and storm surges.  They can be broken and wiped out down to a depth of 20 m, with the branching colonies being much more susceptible to breakage than the more massive forms. The reefs can also be damaged by the sheer influx of freshwater from the storms.
        According to the local Cairns news, "Yasi is expected to be Queensland's worst cyclone, covering something approaching twice the physical size of Cyclone Lary, which devastated the Innisfail region in 2006, causing 1.5 billion AD in damages.

For other posts on this blog about the Australian weather, here's "Santa Never Made it into Darwin", and Inland Tsunami. The Santa post has Super Typhoon Tip for comparison to Yasi.