Fundamentals of Physical Geography 1e Chapter 6: Air Masses and Weather Systems Cover Image. Petersen Sack Gabler

Air Masses and Weather Systems cover image for Chapter 6 (p. 123).

Air Masses Air Mass: large body of air whose temperature and moisture characteristics are similar Source Region: m = Maritime (sea) c = Continental (land) E = Equatorial (very warm) T = Tropical (warm) P = Polar (cold) A = Arctic (very cold) Table 6.1

Air Masses Air Masses Maritime Equatorial (mE) Maritime Tropical (mT) Continental Tropical (cT) Continental Polar (cP) Maritime Polar (mP) Continental Arctic (cA) Table 6.1

Air Masses Table 6.1

Air Masses Air Mass Modification and Stability cP or cA moves over Great Lakes and picks up moisture, and may cause Lake effect snow. What two main factors contribute to increased precipitation caused by the lake effect? Figure 6.1

Air Masses North American Air Masses Continental Arctic (cA) Continental Polar (cP) Maritime Polar (mP) Maritime Tropical (mT) Continental Tropical (cT) Figure 6.2

Air Masses Continental Arctic (cA): Dry and very cold Occasionally impacts U.S. in the winter Often produces record breaking cold Continental Polar (cP): Dry and cold May reach Gulf of Mexico in winter Rarely affects west coast Maritime Polar (mP): Moist and cool Westerlies bring air mass to west coast, especially in winter Occasionally affects eastern U.S. as Nor’easters

Air Masses Maritime Tropical (mT): moist and warm May originates in Gulf of Mexico Major impact on central and eastern U.S T-storms in the summer Clashes with cP Continental Tropical (cT): dry and hot Small source region (SW deserts and N. Mexico Dry line Smallest player in U.S. weather

Air Masses Which air masses affect your location? Are there seasonal variations? Figure 6.2

Fronts Fronts Clash between air masses Sloping boundary Generally move with westerlies 3-dimensional Frontal uplift U.S. and Canada in a zone between source regions

Fronts Cold Front: Cold air moves in on warm air Warm air (less dense) rises above cold air Steep slope Cumulonimbus May form a Squall line Sharp changes in temperature, pressure, and wind Figure 6.3

Cirrus anvil top Warm air mass Cumulonimbus Cold air mass Cumulus Cold front surface Cumulonimbus Cold air mass Cumulus Stepped Art Fig. 6-3, p. 127

Fronts Warm Front: Warm air moves in on cooler air Warm air (less dense) rises above cold air Slope is not as steep Light precipitation which may last longer Usher in warmer conditions Figure 6.4

Warm air mass Cirrus Cirrostratus Warm front surface Altostratus Cool air mass Nimbostratus Figure 7.3 Cross section of a warm front. Warm fronts advance more slowly than cold fronts and replace rather than displace cold air by sliding upward over it. The gentle rise of the warm air produces stratus clouds and gentle rain. Compare Figures 7.2 and 7.3. How are they different? How are they similar? Stratus Stepped Art Fig. 6-4, p. 128

Fronts Stationary Front Occluded Front Boundary between air masses that is not moving Extended period of light precip. and occasionally strong T-storms Occluded Front Cold air is overtaking warm air Dying storm

Four major frontal symbols used on weather maps Figure 6.5

Atmospheric Disturbances Anticyclones and Cyclones Atmospheric disturbance Anticyclone Cyclone Wind and pressure gradient Where would be the strongest winds in this figure? Where would be the weakest winds? Figure 6.6

Atmospheric Disturbances Anticyclone (H) Move with path of westerlies Divergence, sinking air Sources: Northern Canada and Arctic  Polar outbreak Subtropical High  Dry and warmer weather

Atmospheric Disturbances Cyclones Low pressure Convergence and rising air Clouds and precipitation

Atmospheric Disturbances Mapping pressure systems Horizontal structure Vertical Structure Figure 6.6

Atmospheric Disturbances General Movement Track of storms (mid-latitude cyclones) What storm track influences your location? Figure 6.7

Atmospheric Disturbances Middle-Latitude Cyclone Also known as extratropical cyclones Migrating storms Clash between air masses Ex: Cp vs. mT Vary in intensity, longevity, speed of travel, wind strength, amount and type of cloud cover, the quantity and type of precipitation, and the area they affect. Associated with polar front Movement with the seasons

Atmospheric Disturbances Middle-Latitude Cyclone Stages in the development of a mid-latitude cyclone In (c), where would you expect rain to develop. Why? Figure 6.8

Atmospheric Disturbances Cyclones and Local Weather Describe the front(s), temp, air mass type, wind direction, and precip. in Pittsburg and Detroit. Figure 6.9

Atmospheric Disturbances Cyclones and the Upper Air Flow Alternating pressure ridges (highs/divergent winds) and troughs (lows/convergent winds) Where would you expect storms to develop? Figure 6.10

Atmospheric Disturbances Cyclones and the Upper Air Flow Polar Jet Stream Analysis Which country does most of this pattern occupy? Where is one trough? Figure 6.11

Atmospheric Disturbances Hurricanes Circular, cyclonic storm with wind speeds greater than 74 mph Smaller than mid-latitude cyclone Same air mass type More destructive Calm winds at center Also called tropical cyclones Require/fueled by warm water (80oF or more) Figure 6.12

Atmospheric Disturbances Hurricane cross-section Figure 6.12

Atmospheric Disturbances Major “Hurricane Alleys” Which coastlines seem unaffected by these tracks? Figure 6.13

Atmospheric Disturbances Hurricane development Warm water (>27oC or 80oF) Most air Coriolis force (does not form or survive near equator) Stages of development Tropical disturbance (easterly waves) Tropical depression Tropical storm (becomes named; 39-74 mph) Hurricane (categorized by Saffir-Simpson Scale) Dissipation (dies) over land or cool water

Atmospheric Disturbances Hurricane Intensities and Impacts Storm surges Saffir-Simpson Scale What can people who live in such regions do to protect themselves when a serious storm surge is threatening? Figure 6.14

Atmospheric Disturbances Saffir-Simpson Hurricane Scale Table 6.2

Atmospheric Disturbances Hurricane Intensities and Impacts 2004 was a record- breaking year 3 in Florida Hurricane Katrina in 2005 New Orleans Levee failure Hurricane Ike in 2008 Figure 6.15

Atmospheric Disturbances Snow storms and blizzards Mid and high latitudes Blizzard Severe weather event Heavy snow and strong winds (35 mph) Visibility reduced Figure 6.16

Atmospheric Disturbances Thunderstorms Low and mid latitudes Lightning: intense discharge of electricity Thunder: sonic boom created by the expansion of air around the lightning bolt Figure 6.17

Atmospheric Disturbances Types of Thunderstorms Convective (thermal) Orographic Frontal Figure 6.18

Atmospheric Disturbances Tornadoes Occur almost anywhere but are most common in North America (Tornado Alley) Small intense, cyclonic storm of low pressure, violent winds, and converging air Figure 6.19

Destruction caused by an F5 tornado in Greensburg, Kansas on May 16, 2007 Figure 6.20

Atmospheric Disturbances Tornado Typically small and short lived 80% associated with thunderstorms Temporal Variability March to July Late afternoon or early evening Figure 6.21

Atmospheric Disturbances Doppler radar: Improves tornado detection and forecasting Able to determine wind speed and direction Hook Echo is a signature of a tornado Figure 6.22

Atmospheric Disturbances Fujita Scale (F-0 to F-5) Enhanced Fujita Scale (EF-0 to EF-5) Table 6.3

Weather Forecasting Weather Forecasting Doppler radar Weather satellites (e.g. GOES East) High speed computers Improving! Is there cloud cover over your state on this day? Figure 6.23

Fundamentals of Physical Geography 1e End of Chapter 6: Air Masses and Weather Systems Petersen Sack Gabler