outline further reading: chapter 05 of the text book - continental vs. marine regimes - temperature...

Outline

Further Reading: Chapter 05 of the text book

- continental vs. marine regimes

- temperature structure of the atmosphere

- seasonal variations

Natural Environments: The AtmosphereGE 101 – Spring 2007

Boston University

MyneniLecture 11:Temperature-Regimes-02

Feb-09-07(1 of 14)

- urban heat island

Introduction


Boston University


Feb-09-07(2 of 14)

• Previously, we discussed diurnal and seasonal temperature variations based solely on insolation and latitude

• In this lecture, we shall consider other factors (surface type, coastal vs continental location and elevation) to further understand large scale temperature variations

• Need to understand:

– Differences in how radiation interacts with different types of matter, specifically water and land

Oceans


Boston University


Feb-09-07(3 of 14)

• High “specific heat” - can absorb lots of energy w/o much change in temperature (The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius - specific heat of water is 1 calorie/gram °C).

• It’s a fluid -> it can absorb heat at the surface and mix it down into the deeper ocean

• Solar radiation can penetrate past the surface down to approximately 10m

• Most excess energy transformed into latent heat -> does not involve a change in temperature

For oceans, all four result in small, slow changes in temperature ->

the ocean is moderating influence on climate

Land


Boston University


Feb-09-07(4 of 14)

• Low specific heat – does not require much energy to change its temperature • It’s a solid -> can’t mix energy to lower levels so it all stays at the surface• Solar energy can’t penetrate past the surface -> heat only the surface layers• Less excess energy is transformed into latent heat and more into sensible heat, which involves a change in temperature

For land, all four result in large, fast changes of temperature for a small change in energy -> land represents a destabilizing influence

Marine vs Continental Regimes


Boston University


Feb-09-07(5 of 14)

Given the same seasonal change in insolation, the continental climate has much larger changes in temperature than does the marine climate

Continental Climates:Temperature regimes are influenced by thermal characteristics associated with land• Located in continental interiors• Strong seasonality (outside of tropics)• e.g., Chicago….Marine Climates:Temperature patterns influenced by thermal characteristics associated with oceans• Coastal locations• Seasonality modulated• e.g. Seattle


Boston University


Feb-09-07(6 of 14)

• So far, we have been looking at surface temperatures. It turns out that there are also variations in temperature with respect to height (or altitude)

• Temperature structure of the Atmosphere– Troposphere

• Focus of this class• Decrease in temperature with height• Temperature decreases because as you go up, pressure decreases (more

later)– Tropopause - layer of constant temperature representing a transition region– Stratosphere

• Temperature increases with height• Due to the absorption of shortwave radiation by ozone molecules• Ozone hole found here• Very stable (will discuss more later)

Temperature Structure of the Atmosphere-1


Boston University


Feb-09-07(7 of 14)

Thermosphere

Tropopause

Stratosphere

Stratopause

Mesosphere

Troposphere

Temperature

Height

14km

80km

50km

-50 C 25 C


• Temperature structure of the Atmosphere: Discussion continued

– Stratopause - layer of constant temperature representing a transition region

– Mesosphere• Temperature decreases with height• Again due to relationship between pressure and temperature

– Thermosphere• Temperature increases with height• So little gas that molecules move very fast -> there is a very high temperature although there is

very little energy


Boston University


Feb-09-07(8 of 14)



Boston University


Feb-09-07(9 of 14)

Isotherms

• We have now talked about the the four main influences upon surface temperature, namely

– Latitude and insolation

– Continental v. marine

– Altitude

• We can now use these concepts to begin to understand the geographic distribution of temperature

• To do this we look at maps of “isotherms”

• Isotherms:

– Shows where on the map we can find places with the

same temperature


Boston University


Feb-09-07(10 of 14)

Summer Temperatures

– We can see that isotherms run east-west, i.e. temperatures decrease from the equator to the poles (Latitude effect)

– Elevated regions are colder than low regions, i.e. Andes v. Brazil (Elevation or Altitude effect)

– Land areas are warmer than the oceans (Continental v. marine effect)


Boston University


Feb-09-07(11 of 14)

Winter Temperatures

– Now land areas are colder than the oceans (again a Continental v. marine effect)


Boston University


Feb-09-07(12 of 14)

Temperature Seasonality

– There is high variability at high latitudes and low variability near the equator

• Latitude effect on insolation

– High variability at high altitudes; low variability at low altitudes

• Elevation (or altitude) effect associated with thinner air and less greenhouse gases

– High variability over land; low variability near the oceans

• Continental v. marine effect


Boston University


Feb-09-07(13 of 14)

Urban Heat Island Effect-1

• So far we have been talking about geographic features over fairly large spatial scales; now we want to focus on some geographic patterns covering much smaller scales

• Urban Heat Island:

– From this figure, we can see that there is a about a 6-8 degree change in temperature over the span of just 5-10km

– Very predominant in the summer

• So what causes the heat island?

• The predominant factor is the amount of

moisture available for evaporation


Boston University


Feb-09-07(14 of 14)

Urban Heat Island Effect-2

– Transpiration refers to the evaporation of water from the

leaf surface

– Evaporation is the evaporation from the land and open

water surfaces

– Evapo-transpiration is the combined evaporation

from the land surface and the leaf surface

– Rural areas tend to have more available water contained

both in the soil and in the vegetation -> more evaporation

means less sensible heat and smaller temperature changes

outline further reading: chapter 05 of the text book - continental vs. marine regimes - temperature...

Documents

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surface heat

fast changes of temperature

altitude temperature

atmosphere ge

latent heat

energy land