Cyclones and Anticyclones September 19, 2007
Feb 09, 2016
Cyclones and Anticyclones
September 19, 2007
Name that cloud
Atmospheric Pressure Systems
High-pressure system-also called anticyclone-circulating body of air-descending air-clockwise circulation innorthern hemisphere
• Low-pressure system• -also called cyclone• -circulating body of air• -rising air• -counterclockwise circ.• in northern hemisphere
Semi-Permanent Pressure Cells
Thunderstorms
• A typical thunderstorm lasts a few hours
Severe Thunderstorms• Can be single-cell or multi-cell storms• Anticyclonic and cyclonic circulation within
the cell - supercell• Updrafts into the storm can reach 170mi/hr• As supercells move, the anticyclonic an
cyclonic circulation can separate creating 2 supercells
• This is how squall lines and mesoscale convective complexes (MCCs) are created
Supercell Thunderstoms
• Can last 12 hours• Squall lines and MCCs can last longer• Most common during afternoon and early
evening• The sun heats the ground and that heat
rises to the lower atmosphere• This intensifies the contrast between air
temperatures on either side of the coming cold front
Super-cell
Supercell
Supercell
Hail• In a supercell, powerful updrafts carry
water droplets to great altitude• The cold high-altitude air freezes the water• The frozen water then serves as a
condensation nuclei for other water droplets forming hail
• Hail is cycled through the cloud growing larger
• It falls to the ground when it is heavier than the force of the updraft
Hail
• Can be pea to baseball sized• Occur most often between April and
September• Peak between June and July• Can occur in late fall and early spring, but
usually very small
Thunderstorm Wind
• Straight-line (nontornadic) winds called derechos – very powerful and damaging
• Gust front – rush of cool air derechos moving ahead of the storm – can increase by 60mi/hr in seconds
• As rain begins, wind speed decreases• Microbursts also common
Lightning
• Most dangerous aspect of a thunderstorm for human life
• More dangerous than tornadoes• The Troposphere and Ionosphere are
excellent conductors of electric current in the atmosphere
• Between them is the Stratosphere, which is a terrible conductor of electric current
Lightning
• When a poor conductor is between two good conductors, a capacitor is created
• A capacitor has the ability to store electrostatic charge
• The earth-ionosophere capacitor is 8000 mi in diameter and surrounds the Earth
• Vertical air currents and areas of high water vapor content produce channels of high conductivity
Lightning
• Cumulonimbus clouds that reach the Tropopause present a path for electrical discharge
• Discharge can occur slowly or very quickly, as lightning strokes
• Our atmosphere is constantly dissipating 450 megawatts of power