Anticyclone center tracks for month of July for North America.

Source: (Zishka and Smith 1980)

Anticyclone (high pressure) center tracks for month of January for North America.

• Most high pressure systems track southeastward across the middle of the continent from Alaska and the Yukon
  
• Most anticycles end their track near Bermuda
  

Source: (Zishka and Smith 1980)

Cyclone center tracks for month of July for North America. Four main cyclone tracks are indicated according to their regions of origin.

• Cyclones have a more northerly track mostly across northern Canada.
• Cyclone tracks generally ends near Greenland and Iceland
  

Source: (Zishka and Smith 1980)

Cyclone center tracks for month of January for North America. Four main cyclone tracks are inicated according to their regions of origin:

• Pacific lows
• Alberta clippers
• Colorado lows
• Hatteras lows (Atlantic cyclones)

Source: (Zishka and Smith 1980)

Polar and subtropical jets

A jet is defined as any core of fast moving air, often indicated by a curved arrows on maps and by television meteorologists. The line is drawn in the location of the strongest winds. Jetstreams are typically wider and not as distinct, but more of a region where the wind increases toward a core of the strongest wind. One way of visualizing this is consider a river. The river's current is generally the strongest in the center with decreasing strength as one approaches the river's bank. It can be said that jetstreams are "rivers of air".

Observation of winds from rawinsondes show that there are two principle regions in the upper troposphere where winds are strongest. The first is in the 50°-60° N/S region and is called the polar jet and is typically associates with the polar front. The second is called the subtropical jet and is located around 30°N. Jet streams vary in height of four to eight miles (about 500 to 200 mb) and reach a maximum at the tropopause, reaching speeds of more than 275 mph.

The actual appearance of jet streams result from the complex interaction between many variables - such as the location of high and low pressure systems, warm and cold air, and seasonal changes. They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to appear somewhere else. Jet streams also "follow the sun" in that as the sun's elevation increases each day in the spring, the jet streams shifts north moving into Canada by Summer. As Autumn approaches and the sun's elevation decreases, the jet stream moves south into the United States helping to bring cooler air to the country.

Source: NWS

Midlatitude Surface systems

Midlatitude surface systems consist of continental-scale high and low pressure systems.

1. Can you summarize the three most important aspects of the wind circulation around high and low pressure systems?

2. What are the results of these wind circulations for cloud and precipitation formation of these characteristics associated with high and low pressure systems?

3. What are some the consequences of temperature advection associated with each of these systems?

Solution:

	High (anticyclone)	Low (cyclone)
1.	a) clockwise b) outward c) downward	a) counterclockwise b) inward c) upward
2.	downward circulation associated with clear conditions	upward circulation associated with cloud/precipitation
3.	warm advection to west (left in picture) cold advection to east (right in picture)	warm advection to east (right in picture) cold advection to west (left in picture)