e31 locl

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Small Scale and Local Winds Small scale and local winds fall into three categories, 1. Winds that are tied to the local geography (e. g., the sea breeze). 2. Winds that acquire a distinct local character when they pass through a region (e. g., haboobs). 3. Winds that can occur almost anywhere if weather conditions are favorable (e. g., whirlwinds).

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The sea breeze visits most of the world's coastlines. On clear days during the warm season or in the tropics, air over land warmer faster and more than air over the sea and a circulation cell develops. At the ground a cool breeze blows in from the sea to replace rising, warm air over the land. Aloft, air blows out to sea and sinks. At night, the land frequently gets colder than the sea. The circulation then reverses and blows from land to sea as a land breeze. Thus, the sea breeze pulses to a pronounced daily cycle. It usually begins a few hours after dawn. At first it is confined to the immediate vicinity of the beach and is only a few hundred feet deep. As the day progresses, it forges further inland, backs out to sea, and grows deeper unless the air is stable. At its peak, the sea breeze averages between about 10 and 20 mph and temperatures are typically 5 to 30°F cooler on the shore than inland. The sea breeze typically penetrates about 10 miles inland. Outside the tropics the strongest sea breezes occur in spring because the ocean is still cold, but the sea breeze is most regular in summer, when larger-scale winds tend to be weakest. When some strong sea breezes roar in, temperature, wind, and humidity can change abruptly. In such cases the leading edge is called a sea-breeze front. Late in the afternoon, when the sun sinks and the land cools, the sea breeze weakens, and by evening, may reverse. The nightly land breeze is usually much weaker and shallower than the sea breeze because the cool night air near the ground is more stable and slowed more by friction.

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00 UTC 18 July 1998 Sea Breeze: Yucatan Peninsula 15 June 2005 1625 UTC

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Sea Breeze: East Coast Florida, Bahamas 15 June 2005 1620 UTC http://rapidfire.sci.gsfc.nasa.gov/

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Sea Breeze Gulf Coast Florida 15 June 2005 1620 UTC Determine wind direction from the clouds

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15 June 2005 12 UTC

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Sea Breeze 28 March 1998 1500 EST

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12 UTC 17 July 1998

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Katabatic (or fall) wind. Katabatic winds blow downslope from chilled highlands, such as the ice sheets of Greenland and Antarctica and can be among the most violent winds on Earth. The katabatic wind is gentle where the slope is gentle, but furious where the slope is steep, as at Cape Dennison, Antarctica, where gales exceeding 100 mph are common. And the faster the wind becomes, the more it chills and reinforces itself by whipping up snow and ice. In Europe two infamous examples of katabatic winds are the Bora and the Mistral. The Bora (or north wind) rushes from the highlands down to the shores of the Adriatic Sea around Trieste, Slovenia and produces wind gusts up to 100 knots. At such times it is wise for small ships to harbor elsewhere. The Bora is most common during the winter half of the year. It blows when a polar high pressure area sits over the snow-covered mountains and a low pressure area lies further south over the warmer Adriatic Sea. It increases at night, as the air grows even colder and denser. Thus, the Bora like many katabatic winds, is a combination of a downslope wind and a land breeze. No wonder, it is strongest in the hours near dawn and weakest later in the afternoon.

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The Mistral blows down the Rhone River Valley past Arles and Marseilles, and over the Mediterranean Sea. Like the Bora, it forms mainly during winter and early spring when a high pressure area over central France and Germany funnels polar air down the narrow Rhone River Valley south of Lyon. The Mistral is strongest if a low is present to the SE over the Mediterranean Sea. The Mistral's piercing wind and blazing sun are forever linked with some of the intense paintings of Vincent Van Gogh, but even the towns and buildings defer to it. Arles’ narrow, winding streets are designed to slow the wind, and most houses in the region have no doors or windows on the north side. In reality Van Gogh did not cut off his ear, it froze and cracked off during a strong Mistral.

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Conditions for the Bora and the Mistral

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Fig 5. SSM/I Wind Image. 30 Mar 2001 2034Z Fig. 6. SSM/I Water Vapor Image. 30 Mar 2001 2034Z

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www.nrlmry.navy.mil/sat_training/

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The chinook, foehn, Santa Ana, or Zonda are different names for warm, dry downslope winds. They are warm and dry because in passing over the mountains the air acquires latent heat of condensation as it loses vapor. The greatest warming occurs during inversions because then the sinking air from above has much higher potential temperature than the low-lying air it replaces. Chinooks are too warm and light for the air to sink naturally so they only occur when forced by the large-scale wind. Most chinooks are gentle and produce a slow warming, with somewhat dry air. However, when the chinook is forced by strong winds aloft, it can produce strong gusty winds at the surface that may exceed 100 knots and cause rapid warming. The world's highest temperature occurred during a chinook in Azizia, Libya. When a chinook ends, temperature can plummet. The greatest 24-hour temperature fall on record (from 45 to -56°F) occurred in Browning, Montana when a chinook ended abruptly and was replaced by a cold air mass. When the edge of a cold air mass rests against a mountain slope, the chinook can produce astonishingly rapid temperature rises and falls by making the air slosh back and forth. This once happened at the base of the Black Hills in Spearfish, South Dakota. The temperature rose from -4°F to 45°F from 7:30 to 7:32 A,M. on January 22, 1943, and then fell from 54 to -4°F from 9:00 to 9:27 A.M., when the cold air sloshed back into town. These, and several more abrupt temperature changes cracked plate glass windows. Each time the warm air moved in, cold streets and windshields were instantly coated with frost.