Assignments

• Anthes pg. 71, 75-80, 97-98; Willams pg. 1-4, 54-55; Morgan pg. 153-159, 82-85, 91-95
• Writing Assignment 1issued on Wednesday 15^th, and discussed on both the 15^th and 17^th.

Housekeeping

• Homework 1 was due on Wednesday 15^th, then handed back and discussed on Friday the 17^th.
• Handouts of US maps detailing sea surface pressure data for 13^th, 15^th, and 17^th .
• Daily tracking of Hurricane Floyd

Storm Surge

• A storm surge is caused by the force of the wind of a hurricane pushing the water of the ocean on shore. This force creates a wave that can average 5-6 feet in height and can be responsible for flooding in conjunction with heavy rains and ground saturation. Note that not all hurricanes cause a surge. Only those that have a wind that pushes on shore in the same direction as the ocean tide can cause a storm surge. Floyd did not cause any surges. Heavy rains and ground saturation caused the flooding associated with Hurricane Floyd.

Continued discussion of isobars using data charts handed out in class.

• Know what an Isobar is from last weeks lecture.
• In Meteorology:
• A low is labeled on a map by L or the word Low, and is associated with counter clockwise motion or wind circulation.
• A high is labeled on a map by H or the word High, and is associated with clockwise motion or wind circulation.
• Isobars are drawn on a map at four-millibar intervals at the Low in an area, and counting four millibar up to the next isobar line. Generally speaking, low pressure is associated with bad weather and clouds while high pressure is associated with clear skies and good weather. Hence, on a map if one were to see an area with the isobars clustered together, one would associate that area with some kind of storm or atmospheric disturbance. And in those areas that the isobars are widely spread apart, one would assume good weather. One word of caution is that rugged topography affects a wind observations, most often in the west due to the mountainous terrain.

• A hurricane fits within the definition of a Low. Hurricanes are associated with a great pressure drop within a relatively small area with cyclonic wind. Hence the isobars on a sea level chart would be closest at the eye and stacked tightly in four-millibar intervals.
• Pressure observations are taken at very specific altitudes based on half of the sea level pressure, which is 1000 millibar. Hence, the next observation from sea level will be at 500 millibar and the altitude is 1800 feet, then 300 millibar at and altitude of 3600 feet.
• Though hurricanes are very visible on a pressure chart from sea level, they tend not to be very visible at higher altitude because hurricanes have their strongest winds at sea level, which tends to weaken with altitude. This is not the case for most other storms, which have stronger winds at the higher altitudes.
• A High means that there is a general concentration of atmospheric weight.
• Because nature does not like atmospheric lows, air tends to travel from high to low.
• Storms will fluctuate in category and intensity due to friction of land masses and sea temperature.

Coriolis Effect

• The Coriolis Effect is an apparent deflection of an object from a non-rotating observer’s perspective.
• From the Southern Hemisphere this deflection would be to the left.
• From the Northern Hemisphere this deflection would be to the Right.
• Refer to the class web site for a demonstration and explanation of the Coriolis Effect.

When you look at a weather map you would notice that the air really spirals out of surface highs.  The reason for that has to do with the fact that earth is rotating.  As the air moves from high to low pressure in a straight line (which you would notice from space), the earth turns out of its way.  This creates the illusion that the air is spiraling (and that illusion is real to people on the earth's surface moving with the surface).

This Effect is called  " The Coriolis effect "-  Coriolis force is entirely due to the Earth's rotation around its axis.  Corilois force accounts for the fact that air actually does not move in a straight path, directly away from high pressure to low pressure.

We are unaware that the Earth is rotating around us. This rotation accounts for the earth's surface speed of 1035 mph at the Equator and over 700 mph at our latitude. This point moves faster because it must get back to the same place at the same time as the other points, which move at slower speeds.

If a person standing at the North Pole through a ball to a person at 40N, the ball certainly would move in a straight line (discounting friction and gravity).  If it took the ball one hour to move to 40N, an observer in space would notice that the ball did that and moved in a straight line.  However, in the one hour, the person waiting to catch the ball moves eastward 718 miles, out of the path of the ball.  Since that person thinks he is standing stationary on the earth, he assumes that the ball was affected by a force that deflected the ball to its right (to the west).  All frictionless moving objects are affected by Coriolis force. In the Northern Hemisphere, all such objects are deflected to the right of their path, while in the Southern Hemisphere, the deflection is to the left. This includes planes, ships, projectiles, as well as winds, and ocean currents.

Other stuff

• Note that on a weather map if an observation point is a clear circle within a clear circle that this is a symbol for a calm.
• In the Navy web site, if you are looking for the color codes for the hurricane location graphic go to the Text option for the key.
• Note the location of the Jet Stream in southern Canada and northern America for future lectures. Also, note the location of the Gulf Stream off the East Coast of the US.