AT 351 Lab 5 Ocean Circulations and Wind Due in lab: The Week of February 25 th 140 Points Total

Transcription

1 AT 351 Lab 5 Ocean Circulations and Wind Due in lab: The Week of February 25 th 140 Points Total 1. (20 points) If the earth were a smooth, featureless sphere and the atmosphere were horizontally isothermal (equal temperature everywhere), then the constant pressure surfaces would be concentric spheres surrounding the earth like layers of an onion. In particular, the height of a constant pressure surface would be everywhere equal. If we allow for temperature changes, two columns of air that have equal weight but different average temperatures will have different sizes. The diagram below shows two column of air. Each column has a surface pressure of 1000 mb. Column A is 20 degrees colder than the average temperature of column B. a) (10 points) Is the height of the 500 mb surface higher or lower than the 500 mb surface in column A.? Draw in the pressure surfaces as you think they would appear in column A. b) (10 points) Using the conceptual model provided above. Explain why the 500 mb height is lower over the poles than the equator. Where does the pressure gradient force point? From the equator to the pole or from the pole to the equator?

2 2. (20 points) The pressure gradient force is the force that causes fluids to move from and area of high pressure to low pressure. If this were the only force that affected the atmosphere, all winds would blow directly way from high pressure regions toward low pressure regions. (a) (5 points) In the diagram below, draw arrows showing the direction of the pressure gradient force (PGF) (b) (10 points) The second force that acts on a fluid in motion is the Coriolis force (CF). This force is a consequence of the earth s rotation and always acts at a right angle to the wind direction in the Northern Hemisphere. The figure below illustrates the affect the Corilois force has on a parcel of air as it moves from points A to D. Please label the force vectors (PGF and CF) for the parcel of air at points A, B, C and D. Note the arrow indicates the direction of wind motion. (c) (5 points) The winds at point D are said to be in geostrophic balance. Why?

3 3. (10 points) Below is a figure of the upper level (500 mb) constant pressure surface. The solid blue lines denote the height contours. (a) (4 Points) Indicate the direction of the winds in the four regions indicated on the map by letter A, B, C, and D, by draw winding vectors in the specified regions indicating the wind direction. (b) (5 Points) The regions with low heights are called troughs on a constant pressure surface. Regions with higher heights are known as ridges. Put a large L where the heights are lowest and a large H where heights are highest. (c) (6 Points) Name three states you expect the weather to be sunny and three states where you might expect the weather to be cloudy. Sunny:,, Cloudy:,,

4 4. (15 Points) Draw the circulation arrows, an L and an H for a surface Low and High pressures (one for each situation shown), and convergence and divergence on the two diagrams below.

5 5. (15 Points) On the map of sea level pressure (SLP) below, identify centers of High and Low pressure. Where would you expect the winds to be the strongest and in what general direction would they be blowing? What areas of the country might be experiencing clear skies and dry weather? What areas might be seeing stormy weather?

6 6. (15 Points) Calculate the pressure gradient between Salt Lake City (SLC), p 1, and the selected cities, p 2, on the map below. Make sure to convert miles to kilometers (look up the conversion) and review your notes on how to read pressure values off of station plots. PGF = p 1! p 2 DISTANCE

7 a) Elko, NV (EKO, ~ 200 miles away from SLC) b) Las Vegas, NV (LAS, ~350 miles away) c) Grand Canyon, AZ (GCN, ~300 miles away) BONUS: (5 Points) What is the local time in Fort Collins at the time the surface data was recorded? 7. (10 Points) Explain the mechanisms that drive a Land Breeze Circulation. It would probably help to draw a picture. 8. (10 Points) Explain the mechanisms that drive the Summer Monsoon over Southern Asia. It would probably help to draw a picture.

8 9. (10 Points) Describe the ideal conditions for the formation of a Chinook wind. What are the two main reasons that this wind is warm? 10. (15 Points) Draw the main features of the Pacific Ocean circulation AND the overlying air circulation during El Niño conditions. Explain how La Niña conditions are different. Extra Credit (10 Points) Why are sea surface temperatures (SSTs) relatively colder on the western side of continents than they are on the eastern side of continents at the same latitude?