The Indian monsoon is characterized by a reversal in the winds over the Indian subcontinent between summer and winter. In winter, the winds blow off the continent to the SW and in summer (starting in May) they blow from the SE. The wind shift is associated with heavy rains over India in the summer which are relied on for crops.Plot examples using the atlas:
The first two plots illustrate precipitation over India at different phases of the monsoon. Note that the heavy precipitation moves north in summer but that precipitation over the Himalayas does not seem to greatly increase. The annual cycle plot (not shown in talk) shows that the precipitation starts in May and has a slight tendency to move to the north through the summer.Questions that could be asked about these plots include: Why does the precipitation start in May? What kind of wind flow would tend to accompany this pattern? Why does the maximum stop around 30N? Why are there two maximums over India? How does the precipitation relate to orography?
What kind of pressure/temperature pattern would lead to the winds shown? Why are the winds stronger over the ocean?
The air temperature increase in the summer with the maximum tending to move to the north (2nd plot) through the summer. Note the similarity between the precipitation maximum and teh temperature maximum. For the student: 1) What kind of air flow would tend to accompany the increased temperature. Why would the maximum move to the north? Why does the maximum not go above 30N?
How does the vertical motion relate to rainfall? Do you see any vertical motion you don't expect? Why might that be?
El Nino refers to the quasi-periodic increase in ocean temperatures in the eastern tropical Pacific and the resulting circulation changes. El Nino can affect climate in regions away from the tropics.
Note the much warmer than usual temperatures over the eastern tropical Pacific. What kind of circulation would you expect to be associated with these temperatures? How would you expect the difference in temperatures to affect rainfall (primarily convection)? Howdoes this SST pattern compare to other El Nino years (hint, look at a time series of SST averaged over the eastern tropical Pacific)? How does it compare to La Nina years (colder than normal in the eastern Pacific)?
Note that the winds go to westerly over the equatorial region during an El Nino. Is that what you would expect? How would the change in wind speed affect temperature near the surface? What about change in direction?
Note how the precipitation shifts from the western tropical Pacific to further east.What are the changes in midlatitudes (above 20N and below 20S)? Does this happen during every El Nino? What about La Nina years? Is there any other atmospheric variables you can find in midlatitudes associated with an El Nino? (for example temperature, winds, moisture)?
