GENED 1158 Midterm

convection

• Heat transfer process

• Best in fluids

• Warmer part of the mass will rise and the cooler portions will sink

Conduction

The direct transfer of heat from one substance to another substance that it is touching. Through vibration of particles.

Global hydrological cycle

The continuous transfer of water between land, atmosphere and oceans. The Earth is a closed system.

The ocean has greater evaporation rates than precipitation so there is a surplus of water in the atmosphere which is then blown to the land surface. Conversely, the land has more precipitation than it does evapotranspiration. The water thus has to go somewhere. This is called runoff or discharge, the flow of water on or inside the land surface back into the sea.

Unique properties of water

- high latent heat content (energy required when water changes phase)

- Can change phase for typical conditions on Earth

- Very high heat capacity (the amount of energy you need to change water temperature)

mass balance

Given some region (control volume):

• the change in water stored in control volume

• water in - water out

Watershed mass balance

Watershed: set of all points (upstream) that would ultimately route water to the defined outlet point.

A wisely chosen control volume that makes estimating storages in that control volume easier.

Convenient definition because, apart from evapotranspiration, all lateral fluxes occur at a single point, which can be measured.

residence time formula

temperature

• temperature is an indirect measurement of the average kinetic energy of molecules constituting air.

• High temp: high kinetic energy

• Low temp: low kinetic energy

Conservation of Energy

Total energy of a system remains constant, if we account for gains and losses of energy from and to the outside.

Energy cannot be created or destroyed

Energy can be transferred or transformed into different types of energy inside the system:

- Potential energy

- Kinetic energy

- Chemical energy

- Radiative energy

What is pressure?

• Indirect measurement of how much molecules in the air bump into each other

• Force per unit area

• Units:

How to increase pressure?

• Increase the number of molecules in the air parcel

• Decrease the volume of the air parcel

• Increase the temperature of the air parcel

Ideal Gas Law

PV=nRT

What happens to pressure when you increase in height?

Pressure decreases with height

Conservation of momentum

What happens to temperature as you increase in height?

• Up to tropopause: decreases with height

• Tropopause to stratopause: increases with height

• Stratopause until menopause: decreases with height

• Menopause and up: increases with height

Radiation fundamentally dictates the temperature.

dynamic equilibrium

condition of continuous, random movement of particles but no overall change in concentration of materials

Atmospheric thermodynamics

the study of heat-to-work transformations (and their reverse) that take place in the earth's atmosphere and manifest as weather or climate

conduction

• Transfer of heat by transfer of molecular vibrations

• Most efficient in solids

• Not very efficient in air. Only plays an important role in heating air very close to the surface

• Molecules remain in the same place but vibrate

convection

• Cooler, denser air parcels sink while warmer, lighter air parcels rise

• Most efficient in fluids

• Dominating heat transfer process in the atmosphere

radiation

Vibration of molecules creates an electromagnetic field, and the emission of electromagnetic radiation.

When radiation interacts with the atmosphere it can be:

Transmitted

Emission

Absorbed

Reflected or scattered

albedo

Ability of a surface to reflect light

Greenhouse Effect

warming that results when solar radiation is trapped by the atmosphere

variability in radiation

• The emission of infrared radiation by Earth is relatively uniform around the globe, while the absorption of visible radiation from the sun is greater at low latitude that at the poles.

• Differences in albedo

• Ex: beach ball with a flash light shining on it

• There is an energy surplus at the equator and an energy deficit at the poles

Positive feedback loops

Example: Ice-albedo feedback

If ice melts, more will start melting! This is bad for the melting glaciers in the poles.

negative feedback loops

Plancks feedback

temperature increases -> earth emits more infrared radiation -> earth loses energy -> temperature decreases

Seasonal variation

The reason this is experienced is because as it tilts the sun has a different angle coming into the atmosphere and thus different levels of radiation are absorbed.

Diurnal variation

Earth's rotation causes surface temperature fluctuations throughout the day and night.

When does peak temperature occur:

The peak in temperate does not occur at the same time as peak radiation, it is somewhat after

What are four ways land and oceans are different in terms of radiation?

• Land has lower heat capacity than water, so land will increase in temperature more than the ocean

• Energy can be mixed better through convection (over ocean) than by conduction (over land)

• Solar radiation penetrates deeper through water, whereas this does not occur on land because it is opaque

• Over the ocean there is unlimited water, much of the energy that is absorbed in the ocean can be evaporated whereas water on land surfaces is less capable of cooling because of evaporation.

Water phase changes

solid, liquid, gas

saturation

• Air is saturated when evaporation balances condensation

• The amount of water that can be held is a function of the temperature of the parcel.

  • If the parcel is hotter it can hold more water than if it was colder.

humidity

amount of water vapor in the air

absolute humidity

mass of water vapor per volume of air

specific humidity (q)

mass of water vapor per mass of air

Typical values:

q: 0-20 g/kg

mixing ratio

mass of water vapor per mass of “dry” air

Water vapor pressure (e)

pressure exerted in a given volume by water vapor alone, as if all other gases were removed from that volume.

Typical values:

e: 0-3 kPA

Relative Humidity (RH)

the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

Condensation

The change of state from a gas to a liquid

Dew Point temperature (Td)

A measure of humidity in disguise.

Td = the temperature you would need to decrease a parcel of air for it to saturate.

dew point depression

• the difference between the actual temperature and the dew point temperature (T-Td)

• Small dew point depression = air is moist

• Large dew point depression = air is dry

  Dew point temperature cannot be greater than the temperature. It's always less than or equal to the temp.

Diabatically

heat is exchanged with the environment (e.g., radiation cooling)

Adiabatically

no heat is exchanged with the environment (e.g. rising air)

How to saturate an air parcel?

• Add more water vapor (ex: evaporation fog)

• Reducing temperature (either diabatically or adiabatically)

pressure gradient force

Drives air from areas of higher barometric pressure to areas of lower barometric pressure, causing winds.

sea breeze

• Flow of cooler air from over an ocean or lake toward land

• Example of: pressure gradient force

land breeze

• movement of air from land to sea at night

• created when cooler, denser air from the land forces up warmer air over the sea

• example of: Pressure gradient force

Why do winds often not blow from high to low pressure (as dictated by the pressure gradient force in the atmosphere)?

They blow orthogonal due to the Coriolis force.

Coriolis Force

• The apparent force, resulting from the rotation of the Earth, that deflects air or water movement

• Example: Mary-go-round

• Objects in motion in the northern hemisphere are deflected at a right angle and to the right of the direction of motion

• Opposite occurs in the southern hemisphere

• The Coriolis force is zero at the equator, and increases with latitude, reaching a maximum at the poles.

• The Coriolis force is proportional to the wind speed: faster winds lead to stronger deflection.

• Since the Coriolis force is perpendicular to the wind direction, it only affects the wind direction and does not affect the wind speed: it makes the wind veer, but does not accelerate or decelerate it.

geostrophic wind

• A wind that moves parallel to the isobars as a result of the balance between the pressure gradient force and the Coriolis effect

• High pressure: blow clockwise (in northern hemisphere)

• Low pressure: blow counterclockwise (in northern hemisphere)

To identify the direction the winds are blowing:

1. Identity PGF

2. COR balances PGF so points in opposite direction

3. COR points 90 degrees to the right of the wind direction.

What are summers like in West vs. East USA and why?

• West: Pacific high moves cool, dry air down the west coast

• East: Bermuda high brings warm, moist air from the tropics toward Florida and the east coast

The Sahel

The location of the solar maximum varies with the season and the relative position of the Earth to the sun. In the Northern Hemisphere in winter, the sun is slightly south of the equator. In the N. Hemisphere in the summer, the sun is slightly north of the equator. This means a subtle migration of the sun in the winter and summer.

This subtle change is really important to the sahel region of Africa.

Thermodynamics of cloud formation

• Cloud cool via adiabatic cooling

• As the air parcel rises:

  • Pressure decreases

  • Parcel of air expands, doing work on the surrounding atmosphere

  • This uses up energy in the parcel, resulting in a decrease in temperature ("adiabatic cooling")

lifting condensation level (LCL)

Height at which parcel becomes saturated after being lifted adiabatically from the surface

large-scale horizontal convergence

• Uplift occurs because bodies of air with similar proportions collide and move upward

• Convergence of air with similar thermal properties

Frontal convergence

convergence of air with different thermal properties

Orographic uplift

Uplift that occurs when a flowing body of air encounters a mountain range.

Rain falls on one side but not the other

Adiabatic cooling occurs at a rate of:

10*K/km

cloud microphysics

• Condensation

• Liquid water droplets form raindrops

• Potential barriers: evaporation, updrafts

homogeneous nucleation

As air becomes supersaturated, molecules of liquid water combine to form droplets.

However, this process is very inefficient—requiring extremely high levels of supersaturation.

Heterogeneous nucleation

the addition of cloud condensation nuclei helps droplets to grow

cloud condensation nuclei

small airborne particles upon which water vapor condenses to form clouds and rain

Ways to measure rain

• standard rain gauge

• radar (horizontally, bounces off rain)

• satellite (senses T of cloud)

Thermal convection

If a parcel is in an area where the surrounding air is colder than the parcel, it floats.

When do floods occur

When the rate of rain exceeds the capacity of a land surface to absorb the rain (infiltration capacity).

Infiltration capacity

The maximum rate at which rain can be absorbed by a soil in a given condition

Infiltration rates vary by soil type. Sand has large granules so water is absorbed more effectively than clay or cements which is almost 0 absorption.

Why do hurricanes mostly occur in the North Atlantic and West Pacific?

Hurricanes rarely form in SouthAtlantic and Eastern South Pacific because there water is too cold & at the equator there is no Coriolis.force.

Why do hurricanes move east to west?

• Hurricanes form near the equator where the water is warm

• Easterly winds push these hurricanes east

• They begin to shift west when they hit the westerly winds

Why no hurricanes at the equator?

• Wind blows parallel to isobars, with higher pressures on the right (in the northern hemisphere)

• Wind speed is proportional to the pressure gradient (i.e., the tightness of the isobars)

• Winds tend to blow clockwise around highs, and counterclockwise around lows

natural levee

• results from continual flooding

• a deposit of sand or mud built up along, and sloping away from, either side of the flood plain of a river or stream

issues with levees

• overtopping

• seepage through/under the levee

• not protection—postponement

The lower the pressure anomaly:

the greater the hurricane

Geostrophic balance neglects

friction

→ friction is working in opp direction, reducing wind speed therefore reducing the coriolis force. Low pressure spiraling inward, high spiraling outward

Topography

Mountains and buildings have an influence on winds.

Katabatic Winds

• Colder air mass flows down ice and snow slops out to the water

• Very fast winds

• Move down a slope

Valley breeze

The movement of air created by warm air rising and flowing up the slope of a mountain.

What does surplus radiation at the equator imply?

poleward heat transport

Latitudinal heat transport is mainly driven by

the atmosphere at mid and high latitudes

intertropical convergence

• Lots of rain because of ascending air

• Rising warm air creates rainfall

dry spots

• areas of cool air down currents

• parcels of air moving north have lost moisture content from dumping it in other areas

Hadley cells

steady conveyor belt pushing energy north

Turbulent eddies

chaotic and random but have a net effect of pushing wind north.

arctic amplification

• Poles warm more rapidly compared to the equator, reducing the latitudinal temperature gradient

• Positive feedback loop of melting snow and ice isn't a solid explanation

atmospheric jets

Poles warm more rapidly compared to the equator, reducing the latitudinal temperature gradient

implications for weather extremes

• Reduced meridional temperature gradient > reduced baroclinic eddy formation > reduced storm activity and temperature extremes

• Reduced meridional temperature gradient > polar jet slows down > polar jet becomes more undulating --> more frequent and persistent storm activity and temperature extremes

Easterlies blow...

from the east

The albedo of a surface is:

the % of radiation reflected by a surface

Why is the North Pole cooler than the equator during the summer, even though there are 24 hours of daylight per day?

the sun is lower above the horizon at the north pole than at the equator

The amount of incoming solar radiation absorbed by the earth system is equal to:

The amount of infrared radiation emitted by the Earth system.

Summers are warmer than winters because:

The sun is higher in the sky and the days are longer in the summer, due to the tilt of the Earth

The seasons are due to:

The tilt of earth as it orbits

Earth only absorbs solar radiation during daytime, whereas it emits infrared radiation:

day and night

Saturation water vapor pressure

Measures the maximum amount of water vapor that a given volume of air can contain