1) Forcings and feedbacks in the Earth climate system. What is the fundamental difference
between a forcing and a feedback? Give one example of both a forcing and a feedback.
What do we mean when we say a feedback is positive or negative? Is the example you gave
positive or negative?
A forcing is a cause that will make the climate change. Examples are changes in orbital
parameters (e.g. Milankovitch cycles) or changes in atmospheric IR absorption (in/decrease
of CO2 or CH4). Feedbacks are responses to changes in the climate system that themselves
lead to further climate change. Examples are the Planck feedback (negative, a warmer
planet will emit more IR), the sea-ice albedo feedback (positive, a warmer planet will have
less reflecting sea-ice and more absorbing ocean surface).
2) The Hadley cell. Explain what it looks like, why it exists and what role it plays in the
climate system.
The Hadley cell is a large circulation pattern in the atmosphere. It exists because solar
heating and moisture create an unstable and convective atmosphere close to the equator.
Hot air rises and flows northward (or southward on SH) until about 30o latitude where the air
sinks. Once near the surface, the air flows back to the equator. Motion in a Hadley cell is not
directly North-South due to the Coriolis force that turns the surface winds to the west, the
so-called trade winds. The Hadley cell transports heat from the equator to higher latitudes
where it is transferred to the Ferrel cell. Together they account for a large portion of the
meridional heat flow in the Earth system, which is necessary to compensate for radiative
energy losses at high latitudes.
3) Geostrophic flow. Explain it conceptually. Give the equation that describes geostrophic
flow. Is there a difference for geostrophic flow in the atmosphere and ocean?
Geostrophic flow originates from a force balance between a pressure force and the Coriolis
% '(
force. Equation is 𝑓𝑣 = − & ') , with 𝑣 the east/west wind and 𝑦 the distance in north/south
direction (this can be derived from equation sheet). Without the Coriolis force, wind (or
ocean currents) would flow from high to low pressure but due to the Coriolis force these
flows will deviate and (once balance has been achieved) actually flow along lines of constant
pressure. There is no fundamental difference between geostrophic flow in the atmosphere or
ocean.
4) Atlantic thermohaline circulation. Describe its location and structure. Explain why it
exists, the role it plays in the climate system and what current changes in this circulation
may mean.
The thermohaline circulation is a circulation pattern in the ocean, to be precise the Atlantic.
The THC starts with the formation of deep water near Greenland: strong winds make warm
water evaporate and become heavier (more saline) in the process. These waters sink and
start a deep ocean current to the southern hemisphere. Here the deep waters resurface
(rather diffusely) and start a return surface current that brings warm waters from the
equator northward. The THC is an important part of the meridional heat transfer and in
particular warms up Northern Europe. Changes in the THC will lead to changes in regional
between a forcing and a feedback? Give one example of both a forcing and a feedback.
What do we mean when we say a feedback is positive or negative? Is the example you gave
positive or negative?
A forcing is a cause that will make the climate change. Examples are changes in orbital
parameters (e.g. Milankovitch cycles) or changes in atmospheric IR absorption (in/decrease
of CO2 or CH4). Feedbacks are responses to changes in the climate system that themselves
lead to further climate change. Examples are the Planck feedback (negative, a warmer
planet will emit more IR), the sea-ice albedo feedback (positive, a warmer planet will have
less reflecting sea-ice and more absorbing ocean surface).
2) The Hadley cell. Explain what it looks like, why it exists and what role it plays in the
climate system.
The Hadley cell is a large circulation pattern in the atmosphere. It exists because solar
heating and moisture create an unstable and convective atmosphere close to the equator.
Hot air rises and flows northward (or southward on SH) until about 30o latitude where the air
sinks. Once near the surface, the air flows back to the equator. Motion in a Hadley cell is not
directly North-South due to the Coriolis force that turns the surface winds to the west, the
so-called trade winds. The Hadley cell transports heat from the equator to higher latitudes
where it is transferred to the Ferrel cell. Together they account for a large portion of the
meridional heat flow in the Earth system, which is necessary to compensate for radiative
energy losses at high latitudes.
3) Geostrophic flow. Explain it conceptually. Give the equation that describes geostrophic
flow. Is there a difference for geostrophic flow in the atmosphere and ocean?
Geostrophic flow originates from a force balance between a pressure force and the Coriolis
% '(
force. Equation is 𝑓𝑣 = − & ') , with 𝑣 the east/west wind and 𝑦 the distance in north/south
direction (this can be derived from equation sheet). Without the Coriolis force, wind (or
ocean currents) would flow from high to low pressure but due to the Coriolis force these
flows will deviate and (once balance has been achieved) actually flow along lines of constant
pressure. There is no fundamental difference between geostrophic flow in the atmosphere or
ocean.
4) Atlantic thermohaline circulation. Describe its location and structure. Explain why it
exists, the role it plays in the climate system and what current changes in this circulation
may mean.
The thermohaline circulation is a circulation pattern in the ocean, to be precise the Atlantic.
The THC starts with the formation of deep water near Greenland: strong winds make warm
water evaporate and become heavier (more saline) in the process. These waters sink and
start a deep ocean current to the southern hemisphere. Here the deep waters resurface
(rather diffusely) and start a return surface current that brings warm waters from the
equator northward. The THC is an important part of the meridional heat transfer and in
particular warms up Northern Europe. Changes in the THC will lead to changes in regional
