9/30/19

1

Atmospheric and Surface Energy and Moisture Budgets

Energy Budget Components

Why Do We CareAbout Energy Budgets?

• Determines overall climate• Determines local variations in climate• Determines response of climate to

human changes (e.g., agriculture, urbanization) and natural changes

2 nearby locations in the Great Basin Desert – different energy budgets lead to different microclimates

(Sand, gravel)

(Salt flat)

Why the Difference?We will discuss this in the next chapter.

9/30/19

2

How are desert energy budget components different from global

energy budget?

?

M ?

9/30/19

3

L ?

M

?

9/30/19

4

L ?

L ?

9/30/19

5

L ?

L

?

9/30/19

6

M

Moisture Budget Components

Why Care About Details of the Water Budgets?

Determines how much water available for • evaporation• replenishment of water table• plants• runoff to reservoirs, flash floods

Implication for

• Agriculture• Cloud seeding• Emergency response (flooding)• Water management – dams, wells, water

rights

9/30/19

7

? L

? M/L

9/30/19

8

? M

? ? M/L M/L

9/30/19

9

? M/L

Atmospheric and Surface Energy and Moisture Budgets

Focus on Budgets at the Surface to Understand Conditions Where We

Live

9/30/19

10

Surface Radiation Budget

R = (Q+q)(1-a) – I­ + I¯

R – net radiation

Q – direct solar radiationq – diffuse solar radiation

a- albedoI – longwave radiation

Components of surface radiation budget measured at a location in the Great Basin. (cloud-free, September)

Noontime Sun

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ ?

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger

9/30/19

11

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q?

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds

•a?

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds•a - Larger because of less vegetation

9/30/19

12

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds•a - Larger because of less vegetation•I¯ ?

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds•a - Larger because of less vegetation•I¯ - Probably less

9/30/19

13

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds•a - Larger because of less vegetation•I¯ - Probably less•q?

How is net radiation different in the desert?R = (Q+q)(1-a) – I­ + I¯

•I­ - Larger because T-surface is larger•Q – Larger because of less clouds•a - Larger because of less vegetation•I¯ - Probably less•q – Smaller because of less cloud

Surface Energy Budget

R = LE + H + G

R – net radiationLE – latent heat flux (evaporation & transpiration)

H – heat flux to atmosphereG – heat flux into ground

Annually

0

How Would LE, H, and G be different in the desert?

• LE?• Depends on amount of energy and

moisture available• LE – Small or 0 in desert

9/30/19

14

How Would LE, H, and G be different in the desert?

• H?• Depends on the temperature

of the ground (what does this depend on?)

• H probably higher in the desert

How Would LE, H, and G be different in the desert?

• G?• Depends on

- thermal conductivity of substrate (sand, rock, playa)

- amount of energy available• Will discuss this in more detail

in next chapter

The diurnal variation of the components of the surface energy budget for three different surfaces

Noontime Sun

Why are the Energy Budget components different?

Fig. 4.15 The annual variation of the surface energy budget components at three different locations

Why are the Energy Budget components different?

9/30/19

15

The Oasis Effect –An energy budget peculiar to the desert

What causes LE to be larger than R?

Oasis – Death Valley

Desert Heat

• More solar energy input to surface because of less cloud (connection between water budget and energy budget)

• Drier substrate, so less solar energy lost to evaporation and more available for heating surface (and atmosphere)

• Hotter surface means more heat input to atmosphere and substrate