SECTION 3 Air Pressure Map Analysis pheressure areas that exist in the atmos er
ID: 290515 • Letter: S
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SECTION 3 Air Pressure Map Analysis pheressure areas that exist in the atmos er pressure. Isobars facilitate the spatial analysis of phere principally result from unequal heating at Earth's pressure patterns and are surface and from certain dynamic forces in the atmos- ion, interpretation, and forecasting phere. A map of pressure patterns is accomplished by using isobars, lines that sure. As lines and isotherms-the key to weather map prepara- Sea-level atmospheric pressure averages for connect points of equal pres- January and July are portrayed in Figures 7.2 and 7.3. with other isolines that we have used contour These maps use long-term measurements from surface distance between isobars indi stations and ship reports generally taken from the of pressure diference, or pressure 1950s to 1970s, with some ship data going back to the last half of the 19th century gradient, which is the change in atmospheric pressure over distance between areas of higher pressure and Surface air pressure map analysis: Just as closer contour lines on a topographic map mark a steeper slope and closer isotherms (Lab Exercise 6) eeper temperature gradients, so do closer isobars denote steepness in the pressure gradient. Isobars spaced at es from one another mark a more gradual pressure gradient, one that creates a slower air flow. A steep gradient causes faster air movement from a high-pressure area to a low-pressure tudes (gradual pressure gradient -weaker winds) and between 40°-70° S latitudes (steeper pressure gradient late (estimate) the pressure value to mark on the graph. 1. Use the four graphs in Figures 7.4a, 7.4b, 7.5a, and 7.5b to plot pressure data along two parallels and two meridians area In Figure 7.2 (January), note the spacing of the isobars along the 90 W meridian between 40-70° N lati- stronger winds). As you use the maps in Figures 7.2 and 7.3, remember these maps use a 2-mb interval (e.g.. 1020 mb, 1018 mb, 1016 mb, etc.). If the data points you are plotting fall between two isobars, you can interpo- as noted then complete the pressure profile with a line graph connecting the plotted data points (Cor every 20P): a) January (Figure 7.2), along 50° N parallel (already done for you) b) January (Figure 7.2), along 90 W meridian e) July (Figure 7.3), along 40° N parallel d) July (Figure 7.3), along 60° E meridian After completing the plotting of pressure data on graphs in Figures 7.Aa, 7.4b, 7.5a, and 7.5b, complete the following. 2. Using these maps and your textbook explain the patterns of average atmospheric pressure over the land- masses. Are the patterns of high and low pressure caused by thermal or dynamic foces? a) January:Explanation / Answer
It is a very simple task. But the maps of fig 7.2 and 7.3 must be given so as to take observation of the values of pressure to plot on graph.
2. January: During January the Northern hemisphere experiences winter and the lands get colder while the water bodies are still not so cold( because water has high specific heat capacity , it cools and heats up very slowly). So there is high pressure on the land while low pressure on the water bodies.
In contrast the southern hemisphere experiences summer in January, so the lands are hotter causing low pressure over them while the water bodies are relatively cold so high pressure.
If we see the pattern of global pressure belts then we can observe that the low pressure belts of tropical regions shifts towards southern hemisphere, itcz belt also shifts a little south. The high pressure belt of North pole extends in width while that of south pole shrinks.
B. July: In July the conditions on both hemisphere get reversed. Now it's summer in North hemisphere and winter in southern hemisphere. So the land in North hemisphere gets hotter and thus low pressure while the water bodies have high-pressure. In southern hemisphere lands have high pressure and the water bodies are at lower pressure. The high pressure belts of North pole shrinks and that of south pole expands. The itcz shifts a little north.
These high and low pressure belts shifts according to thermal and dynamic conditions. The tilt of the earth's rotational axis causes alternate seasons in the two hemisphere causing heating in both in different seasons and thus different atmospheric pressure. The rotation of the earth causes coriollis effect producing global wind gyres that work to equilibrate the pressure contrast.
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