EARTH SCIENCE LAB
Wind


Surface Wind

Wind is the movement of air from areas of higher pressure to areas of lower pressure. In an ideal situation, air moves directly from higher pressure areas to lower pressure areas. Graphically, the wind would appear to blow perpendicular to the isobars. However, since the Earth is a rotating body, the ideal situation does not normally exist. Coriolis Effect alters the apparent path of the moving air. In the northern hemisphere the deflection is to the right, while in the southern hemisphere the deflection is to the left. Graphically, wind will appear to move across the isobars at an angle.


Surface wind diagram

1. On the surface isobar map, draw wind arrows representing surface winds. Each arrow should be drawn as a short, straight arrow, between 0.5 and 1 cm in length. Do not draw the wind arrow as a curved arrow. Each arrow must cross the isobar. Draw an arrow every 2 cm on all isobar lines (in other words, completely fill the map with wind arrows).

Wind Speed and Direction

The two of the measurements needed to characterize air movement are wind speed and wind direction. Wind speed is a measure of the velocity of the wind, usually in kilometers per hour or meters per second (unfortunately, the United States continues to use the English system and so wind speed is usually reported to the public as miles per hour). This measurement is made using an anemometer - a device which often has three or four cups mounted on a vertical, rotating rod. The cups catch the wind and spin. Once this device is calibrated it allows for the measurement of the wind speed.

Wind direction is a measurement of the direction from which the wind is coming. Hence, a north wind is one which is coming from the north and going to the south. There are two ways in which wind direction is reported. One system uses the compass directions of north, south, east and west, with quarter divisions between these major directions . This is the system most commonly reported on the local weather reports. Most scientific measurements use the angle measurements of degrees. In this system north is 0 degrees, east is 90 degrees, south is 180 degrees and west is 270 degrees.


Wind direction diagram 360 degree circle diagram

Manila, Philippines: 14°37'N Lat., 120°58'E Long.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average Speed, m/s 6.69 5.59 5.09 4.13 3.56 4.84 4.49 5.80 4.45 4.95 6.55 7.43
Direction, degrees 59 62 67 69 72 79 84 98 104 99 88 80

Valdivia, Chile: 39°46'S Lat., 73°15'W Long.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average Speed, m/s 5.91 5.66 5.59 5.81 6.54 6.37 6.46 6.06 6.00 5.92 5.71 6.02
Direction, degrees 229 227 230 239 252 264 274 279 281 279 275 272

Mona, Utah: 39°48'N Lat., 111°51'W Long.
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average Speed, m/s 4.55 4.70 4.76 4.84 4.87 4.88 4.75 4.65 4.97 4.54 4.78 4.55
Direction, degrees 196 213 227 235 227 226 230 233 231 231 232 231

2. Using the data in the tables above, calculate the annual average wind speed for each location. Convert this average to kilometers per hour and miles per hour. Report all values to 2 decimal places.
     Manila, Philippines: meters/second
     Manila, Philippines: kilometers per hour
     Manila, Philippines: miles per hour
     Valdivia, Chile: meters/second
     Valdivia, Chile: kilometers per hour
     Valdivia, Chile: miles per hour
     Mona, Utah: meters/second
     Mona, Utah: kilometers per hour
     Mona, Utah: miles per hour

3. Using the data in the tables above, calculate the annual average wind direction for each location in degrees (report to the nearest degree). Convert this average to nearest compass direction (i.e. N, SE, WNW, SSW).
     Manila: degrees
     Manila: compass direction
     Valdivia: degrees
     Valdivia: compass direction
     Mona: degrees
     Mona: compass direction

4. Using the information from the data in the tables above and answers in the previous problem, determine the major wind belt for each location.
     Manila:
     Valdivia:
     Mona:

Geostrophic Winds

Movement of air at high altitude is still affected by the Coriolis Effect. However, due to a reduction in friction with the surface, high altitude winds do not cross the isobars, but flow parallel to the isobars.


High altitude wind diagram

5. On the geostrophic isobar map, draw wind arrows representing high altitude winds. Each arrow should be drawn as a short, straight arrow, between 0.5 and 1 cm in length. Do not draw the wind arrow as a curved arrow. Draw an arrow every 2 cm on all isobar lines (in other words, completely fill the map with wind arrows).