Earth 111 Hadley Cells and The Orographic Effect

To complete this exercise it is imperative that you have reviewed and understand all of the material presented in Unit 1 Module 2: Climatology of Water.

I. Relative Humidity

Let’s assume that a volume of airat the base of the Hadley Cell at location Athe equator (EQ)starts out both very warm (say, 28° C) and nearly saturated (containing 21 g water per kg air). As the air rises above the equator it cools to 1° Cat the top of the cell (location B).Location C represents the base of the cell at sea level after the air descends at ~30 degrees N or S latitude.

1. On the graph, plot and label points corresponding to points A, B, and C using the information provided above and what you have learned from module 2.*Hint… remember what you have learned about supersaturation!

2. On the graph, using a dashed line and small arrows ( ),sketch the path (temperature water content of air) of the volume of air as it travels through the Hadley Cell from points A to B to C.Note: for simplification assume no new moisture is added to the system.*Hint… see hint above!

3. Showing your work below, calculate the relative humidity of the volume of air at points A, B, and C.

II. The Western U.S. and California Example: Does orographic precipitation really happen?

Here we will explore how the orographic effect influences (or not) precipitation patterns in the western US. Note: positions A and A’ refer to the longitudinal position shown on the map in question 5 and are just for a spatial reference.

  1. Using the data table (last page of your lab), plot a topographic profile across California:

  1. Now, plot the average annual precipitation along the same longitudinal profile below:

  1. Write paragraph discussing the patterns of precipitation from West to East. Are the data consistent with your expectations based on the orographic effect? Or not? Explain.
  1. Why are some locations at very high elevation relatively dry (e.g., Carson City or Topaz Lake), whereas some locations at relatively low elevation are moderately wet (e.g. Sebastopol)? Please explain your reasoning relating it to what you have learned.
  1. On the map of the Western US below:

A) Neatly sketch the following mountain chains using small triangles(Δ) to denote their extent: Sierra Nevada, Rockies, Olympics, Coast Ranges, and the Cascades. Neatly label each range.

B) Now, by lightly coloring (or using a lightly shaded polygon) indicate areas that you expect to have low, moderate, and high annual precipitation using the following colors: (low = light blue; moderate = yellow; high = light pink; neatly label with L, M, and H, respectively). Think about both the orographic effect and global atmospheric circulation patterns.

Data Table for Part II

LocationLongitudeelevation (m) precipitation (in/yr)

Auburn / 121.06 / 387 / 38.5
Big Canyon / 120.90 / 259 / 32.8
Blue Canyon / 120.20 / 1609 / 67.7
Calaveras / 120.31 / 1430 / 54.5
Calistoga / 122.58 / 112 / 37.4
Carson City (NV) / 119.76 / 1417 / 11.2
Davis / 121.76 / 18 / 17.3
Echo Summit / 120.03 / 2240 / 50.8
Grizzly Flats / 120.51 / 1177 / 48.9
Napa / 122.30 / 18 / 24.1
Placerville / 120.73 / 839 / 39.9
Point Reyes / 123.80 / 9 / 25.5
Sacramento / 121.50 / 5 / 17.4
Sebastopol / 122.81 / 20 / 31.6
Sonoma / 122.46 / 29 / 29.5
Topaz Lake / 119.55 / 1537 / 8.4
Truckee / 120.15 / 1834 / 32.1
Volcanoville / 120.78 / 927 / 45.9

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