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."

Terribly Beautiful: The Fluid Mechanics of Industrial Pollution

An open pit pond holding slurry from hydraulic fracturing
Photo by J. Henry Fair

Time Magazine on-line April 20, 2011, had a collection of J. Henry Fair's air photos of industrial pollution. Fair is a photographer whose goal is "to make aesthetically pleasing photographs," to further his mission that "the viewer will come away with an innate understanding of [his or] her complicity [in industrial pollution] and a will to make a difference." The images are published in Fair's first book, "The Day After Tomorrow: Images of Our Earth in Crisis." Fair relies on complementary charter flights from Lighthawk and Southwings, two volunteer-based aviation organizations, to provide his photographic platform in the air.  He's documented the wastes associated with our extraction industries.  The photos in the Time article include bauxite waste from aluminum smelting, tailings from the extraction of oil from tar sands, the oil spreading from the BP Macondo well blowout, and a wastewater pool at a hydrofluoric acid plant, as well as others. All show beautiful fluid dynamics features.

Melt ponds and meandering streams on an ice island--cool!

Peterman Ice Island, Image from NASA
Astronaut photograph taken on August 29, 2011from the International Space Station

More than a year ago, a chunk of ice five times the size of Manhattan broke off of Greenland's Petermann Glacier (reference for this post is here.) It is smaller now (4 x 3.5 kilometers), having splintered several times in its journey of a few thousand kilometers on the ocean. This piece is referred to as Petermann Ice Island A, fragment 2, and it is currently off the northeast coast of Newfoundland. During August it became stuck for 11 days on a shoal or shallow sea floor. It broke free on August 18, but within a week had split into two large pieces.

The image is NASA's Earth Observatory image of the day today (Sept. 16), and the accompanying description discusses how it is behaving in some ways as if it was still a glacier instead of an iceberg. Specifically, during these warm summer months ice on top melts and water forms streams and ponds as it moves downhill toward the edges of the ice.  Sometimes the water hits a crevass and drains out the bottom of the ice instead of making it all the way to the edge.

The features that caught my eye in this photo above are the incredible meandering streams.More than a year ago, a chunk of ice five times the size of Manhattan broke off of Greenland's Petermann Glacier (reference for this post is here.) It is smaller now (4 x 3.5 kilometers), having splintered several times in its journey of a few thousand kilometers on the ocean. This piece is referred to as Petermann Ice Island A, fragment 2, and it is currently off the northeast coast of Newfoundland. During August it became stuck for 11 days on a shoal or shallow sea floor. It broke free on August 18, but within a week had split into two large pieces.

Back in the 1970's these so-called supraglacial streams were a topic of considerable interest, but it appears that not much has been done recently, and possibly nothing on these streams on ice islands.  Leopold and Wolman observed that they were similar in form to alluvial meandering streams, and noted that since they don't carry sediment, the meanders have a hydrodynamic origin. According to Ferguson (ref below) they form in unfissured hollows that experience appreciable surface ablation and where meltwater from a "sufficiently large" drainage area is concentrated.  It is not clear if they originate on the surface bare ice or not.  Ablation reaches its peak in late spring and early summer when extensive winter snow cover remains. The streams seem to develop at the interface between saturated snowpack and underlying ice, which means that they may already be well established when they become obvious at the surface.  Old channels survive for many years because once cut, the only way that they can be obliterated is by ablation. They erode by frictional melting of the channels, but preferential melting along crystal boundaries may be important, and solar radiation penetrating through flowing water can melt the channel bed as well. Ferguson showed that stream widths are proportional to the square root of the (presumeably peak) discharge (discharge in a glacial environment depends strongly on the time of day.

Parker (1975) studied these and concluded that the instability that triggers the meanders only occurs in supercritical flow, and that the meander pattern does not migrate downstream. He found that the meander wavelength is determined by channel width, depth, and Froude number.

Ferguson, R.I., Sinuosity of supraglacial streams, Bulletin of the Geological Society of America, v. 84, 251-256, 1973.

Parker, G., Meandering of mupraglacial melt streams, Water Resources Research, 11(4), 551-552, 1975.

Batu Tara, Indonesia, spectacular photo

Batu Tara, August 18, 2001
Photo by Thorsten Bockel-http://www.tboeckel.de

VPOW featured this beautiful image this week. I was fascinated by the features at the lower left and center bottom--they look like fireworks on July 4, but come, instead, from the impact of volcanic bombs on the slopes near the vent.

Batu Tara is a small stratovolcano that forms an isolated island in the Flores Sea. Normally covered with vegetation, its first historical eruption occurred from 1847-1852, and the current eruption cycle, starting in 2006, is only the second. A pilot reported an ash cloud that year, but there was no other confirmation.  In 2007, MODIS infrared satellite data showed thermal anomalies.  A continuous low-level plume developed on March 15, 2007, and residents on an island about 50 km south reported a 500-1500 m plume. Lava flows were observed in April of that year, and ash plumes were fairly continuous. Here is the Smithsonian compilation of monthly reports on the activity.

Cleveland Volcano in Alaska may erupt soon!

Cleveland Volcano, AVO image

The Alaska Volcano Observatory has announced that Cleveland Volcano's lava dome has expanded from 262 feet diameter on August 30 to 394 feet today. The dome is in the summit crater and fills the floor of the crater.  They've been having trouble with the webcam, but it's here in case you want to check it out.

 Volcano is in the Aleutians, 940 miles southwest of Anchorage. The dome may spill over onto the flanks with lava flows, or there could be small or large explosive eruptions. There is not a real-time seismic network on the remote volcano.

Cleveland is a stratovolcano, with a beautifully symmetric conical form. The base is 8.5 km diameter, and it is 5,676' high. It comprises the entire western half of Chuginadak Island.  Chuginadak refers to the Aleut fire goddess, though to live in the volcano. It is a subduction zone volcano, overlying the Pacific plate plunging under North America. Cleveland is one of the" Islands of Four Mountains," a name given by the Russian cartographers in the 1800's. It is named after the then-president Grover Cleveland (sometime during his presidencies from 1885-1889 and 1893-1897).

It's eruptions are generally vulcanian and strombolian, short explosive bursts, sometimes accompanied by a'a flows, lava fountains, and ash and steam emissions. It has been intermittently active for the last 60 years, with three eruptions in 2009, and two in 2010.

Mariner's 1-2-3 rule and the cone of uncertainty for Katia

Hurricane tracks for the 2005 season, from NOAA

Updated: 9/5/11--new graphic of Katia's projected path added.

I've been curious about the likely track that Hurricane Katia will take, and thought that it would be interesting to look at the tracks that other hurricanes have taken when the have been about where Katia is today (longitude about 55 W, latitude about 20 N.)  It didn't take long to figure out that hurricanes seem to be distinct individuals with a mind of their own! No wonder hurricane forcasting is so difficult! One NOAA scientist interviewed this week commented that they had had the track of Irene predicted fairly accurately, but that getting the intensity right is the difficult part.

Katia and its project path, Saturday Sept. 3 to Thurs Sept. 8
NOAA

It's difficult to control formatting in Blogger, but I've tried to make these two images similar in latitude scale. Notice how the cones of uncertainty for Katia and Tropical Storm Lee in the Gulf of Mexico are just overlapping.

Trajectory predicted 9/05/11
NOAA

The "Mariner's 1-2-3 Rule" says that the National Hurricane Center forecasts have uncertainties of 100-200-300 nautical miles at times ahead of 24-48-72 hours respectively. This rule determines the basic "cone of uncertainty" that you see in all the forecasts. In practice, it looks like NOAA scientists do something slightly more complicated. For a five-day forecast, they place a set of imaginary circles along the forecast track at the 12, 24, 36, 48, 72, 96, and 120 h positions. The size of each circle is set so that "it encloses 67% of the previous five years official forecast errors."  It is broadened beyond the strict 1-2-3 rule to reflect estimated boundaries of the maximum tropical storm force winds (34 knots) at each of these times. The entire track of a tropical cyclone remains within the cone roughly 60-70% of the time.

More information is available here.