FRONTS - Stationary - Occluded

FRONTS – Stationary & Occluded : 

FRONTS – Stationary & Occluded COLD FRONT WARM FRONT STATIONARY FRONTS – a front that is not moving OCCLUDED FRONTS - COLD OCCLUDED FRONT - WARM OCCLUDED FRONT Front Animation: http://www.stevemcentee.com/animation3.html (website last visited: 16 feb 2010) Compiled By: ARVIND TIRKEY

STATIONARY FRONT : 

STATIONARY FRONT A Stationary front is a boundary between two different air masses, neither of which is strong enough to replace the other. A wide variety of weather is found. Usually clouds, prolonged precipitation and storm rains are found there. Where the warm and cool air meet, water vapor in the warm air condenses into rain, snow, log or clouds. A stationary front can remain stalled over an area for many days. A noticeable temperature change and/or shift in wind direction is commonly observed when crossing from one side of a stationary front to the other. Stationary front: either dissipate after several days or devolve into shear lines. Can change into a cold or warm front if conditions changes. 2 Compiled by: ARVIND TIRKEY

Stationary Front Cross-section : 

Stationary Front Cross-section 3 Compiled by: ARVIND TIRKEY

SYMBOL A stationary front is represented by alternating blue and red lines with blue triangle pointing towards the warmer air and red semicircles pointing towards the colder air. : 

SYMBOL A stationary front is represented by alternating blue and red lines with blue triangle pointing towards the warmer air and red semicircles pointing towards the colder air. 4 Compiled by: ARVIND TIRKEY

Example: Although multiple air masses are commonly present over North America, the transition from one to the other can be so gradual and over such a great distance that no front will exist. If the contrast between air masses is sharper and occurs over a shorter distance, then a front is said to exist; if neither air mass is advancing, it’s called a stationary front. : 

Example: Although multiple air masses are commonly present over North America, the transition from one to the other can be so gradual and over such a great distance that no front will exist. If the contrast between air masses is sharper and occurs over a shorter distance, then a front is said to exist; if neither air mass is advancing, it’s called a stationary front. 5 Compiled by: ARVIND TIRKEY

Occluded Front Cross-Section : 

Occluded Front Cross-Section 6 Compiled by: ARVIND TIRKEY

OCCLUDED FRONT DEFINITION : 

OCCLUDED FRONT DEFINITION Sometimes a cold front follows right behind a warm front. A warm air mass pushed into a colder air (the warm front) and then another cold air mass pushes into the warm air mass (the cold front). Because cold fronts move faster, the cold front is likely to overtake the warm front. This is known as an occluded front. 7 Compiled by: ARVIND TIRKEY

SYMBOL Symbolically, an occluded front is represented by a solid line with alternating triangles and circles pointing in the direction the front is moving. On colored weather maps, an occluded front is drawn with a solid purple line. : 

SYMBOL Symbolically, an occluded front is represented by a solid line with alternating triangles and circles pointing in the direction the front is moving. On colored weather maps, an occluded front is drawn with a solid purple line. 8 Compiled by: ARVIND TIRKEY

Formation of Occluded Front : 

Formation of Occluded Front The diagrams above show the formation of an occluded front. When depression (or a low pressure system) forms, it usually consists of a warm front and a faster moving cold front. This can be seen in the top left diagram. To the north of the warm front is the cool air that was in the area before the depression developed. 9 Compiled by: ARVIND TIRKEY

Slide 10: 

Compiled by: ARVIND TIRKEY 10 OCCLUDED FRONT facts....... Occluded fronts usually form around areas of low atmospheric pressure. There is often precipitation along an occluded front from cumulonimbus or nimbostratus clouds. Wind changes direction as the front passes and the temperature changes too. (temperature may warm or cool) After the front passes, the sky is usually clearer and the air is drier.

COLD OCCLUSION : 

COLD OCCLUSION Air behind the occluded front is colder than the air ahead of it. The cold occlusion acts in a similar way to a cold front. The cold air behind the front undercuts the cool air ahead of it 11 Compiled by: ARVIND TIRKEY

COLD OCCLUSION : 

COLD OCCLUSION Cold front lifts the warm front up and over the very cold air. Weather conditions are similar to a warm front as the occluded front approaches. Once the front has passed, the associated weather is similar to a cold front. Vertical structure is often difficult to observe. 12 Compiled by: ARVIND TIRKEY

COLD OCCLUSION Weather Map (areal view) : 

Compiled by: ARVIND TIRKEY 13 COLD OCCLUSION Weather Map (areal view)

Slide 14: 

WARM OCCLUSION The air behind the occluded front is warmer than the air ahead of it. The warm occlusion acts in a similar way to a warm front. The cool air behind the font is lighter than the cold air ahead of the front. This cause the cool air to pass over the top of the cold air. 14 Compiled by: ARVIND TIRKEY

WARM OCCLUSION : 

WARM OCCLUSION Cold air behind cold front is not dense enough to lift cold air ahead of warm front. Cold front rides up and over the warm front. Upper-level cold front reached station before surface warm occlusion. 15 Compiled by: ARVIND TIRKEY

COLD OCCLUSION Weather Map (areal view) : 

Compiled by: ARVIND TIRKEY 16 COLD OCCLUSION Weather Map (areal view)

BIBLIOGRAPHY : 

BIBLIOGRAPHY Information & Images (all website last visited on 16 feb 2010 http://apollo.lsc.vsc.edu http://www.physicalgeography.net http://ww2010.atmos.uiuc.edu http://en.wikipedia.org/wiki/Occluded_front http://www.windows.ucar.edu http://www.ecn.ac.uk http://www.on.ec.gc.ca http://geographyfieldwork.com/FrontalRain.htm 17 Compiled by: ARVIND TIRKEY