HONORS GEOGRAPHY: METEOROLOGY

FRONTAL SYSTEMS - air masses are moved around the globe by winds - creating weather - when air mass arrives in a region, it displaces the existing mass - boundaries or leading edge b/t different masses is a front - when cold air replaces warm air it’s a cold front - when warm air rides over a cold air mass, a warm front - the interaction of these systems may produce a low - creating unsettled weather - esp. in middle latitudes - when warm front moves into area of cold air, rises over the cold and cools - condensation may follow, resulting in cloud formation - first clouds to appear usually cirrus clouds - high wispy clouds in the upper atmosphere - these are normally followed by layer of middle level clouds - then thick stratus clouds in the lower levels - these produce widespread precipitation - and maybe strong winds - this could last up to a day - cold fronts are usually associated with low pressure systems - producing more volatile weather than warm fronts - when a cold front moves into an area of warm air - the warm air is less dense, so forced sharply up by cold air - creating instability and powerful convection - large cumulus and even cumulonimbus clouds may form - triggering storms along the front - also creates area of low pressure - which strengthens winds - rain and winds will be strongest along the front - with showers following - low pressure cells occur when cold and warm air interact - forming a rotating weather system - this process is called cyclogenesis - when the air masses meet, warm air rises - creating a low pressure area at the surface - where clouds and precipitation develop - the heavier cold air is pulled under it - speeding up the cold front - it catches up with the warm front - forcing more air upward - as air rises and pressure falls, more air is pulled into the system - developing into strong winds - in the N. Hem. these winds blow counterclockwise - around a low pressure area - in S. Hem. it’s the opposite - around 24 hours later (often sooner) cold front catches warm front - forming an occluded front - cutting off supply of warm air to the system - the air that rose begins to cool - stopping the rain and winds - essentially the storm is over - high pressure systems normally result from air sinking then rotating - clockwise in N. Hem., counter in S. Hem. - consequently these high pressure systems are called anti-cyclones - usually occur at 30' N & S - sometimes also called warm high pressure. - high pressure areas also happen in cold areas - where cold air, being denser, sinks to the ground increasing pressure - this often occurs during winter - less heat during day - dramatic cooling at night - esp. if no clouds - which can keep in the heat - this is a cold high pressure system - common in inland middle latitudes - Siberia, Canada