Outline

1. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (1 of 14) Further Reading: Chapter 05 of the text book Outline - continental vs. marine regimes - temperature structure of the atmosphere - seasonal variations - urban heat island

2. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University 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 Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (2 of 14) Introduction

3. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (3 of 14) Oceans • 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

4. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (4 of 14) Land • 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

5. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (5 of 14) Marine vs Continental Regimes • 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 Given the same seasonal change in insolation, the continental climate has much larger changes in temperature than does the marine climate

6. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University 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) Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (6 of 14) Temperature Structure of the Atmosphere-1

7. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (7 of 14) Temperature Structure of the Atmosphere-2 Thermosphere 80km Mesosphere 50km Stratopause Height Stratosphere Tropopause 14km Troposphere -50 C 25 C Temperature

8. 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 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (8 of 14) Temperature Structure of the Atmosphere-3

9. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 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

10. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 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)

11. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 Feb-09-07 (11 of 14) Winter Temperatures • Now land areas are colder than the oceans (again a Continental v. marine effect)

12. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 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

13. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 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

14. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni Lecture 11:Temperature-Regimes-02 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