Lecture Oct 18

Today’s lecture

• Quiz returned on Monday – See Lis if you didn’t get yours – Quiz average 7.5 STD 2

• Review from Monday– Calculate speed of air moved from

equator to 30 North

• How Satellites view Earth– Wavelengths and Atmospheric Window

Tropics have a surplus of energy and the poles a deficit. A net poleward transport of energy is therefore required.

ENERGY

Winds Patterns Balance of 3 forces

1. The pressure gradient force causes wind to blow from high pressure toward low pressure.

2. The coriolis force causes wind to be deflected to the right of the motion in the northern hemisphere.

3. Friction which slows the wind.

http://teacherresourceexchange.org/science/coriolis/index.php

The poleward transport of energy occurs in the fronts and low pressure systems of the middle latitudes.

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Satellite image of the United States

As light travels through our universe wavelengths of light stretch!

Light: Color and Wavelength

Distance (nanometers: millionths of a millimeter)

Violet (400 nm)

Indigo (425 nm)

Blue (450 nm)

Green (525 nm)

Yellow (575 nm)

Orange (615 nm)

Red (700 nm)

There Are Many ‘Colors’ We Can’t See!

Radio

Microw

avesInfrared

Red

Orange

Yellow

Green

Blue

Violet

Ultraviolet

X R

aysG

amm

a R

ays

Wavelengths of Light

Light emitted by the Sun

http://feps.as.arizona.edu/outreach/bbplot.html

Wavelength of Peak emission = 2898 microns / Temperature of Blackbody (K).

Emission by the Earth (288K)

http://www.utsc.utoronto.ca/~shaver/blackbody.jpg

http://ceos.cnes.fr:8100/cdrom-00b/ceos1/science/dg/dg9.htm

Visible Light

Infrared Light

Visible

InfraredUV

Visible- Satellite images in the visible band are from reflected sunlight

How much of the Earth’s Energy is absorbed by our atmosphere?

Visible

InfraredUV

Atmospheric Window - Wavelength region of infrared satellite images- responds to the temperature of the cloud tops.

Atmospheric Window: Important to the energy balance of the planet.

A body at 288 K (Earth) temperature emits most of its energy in this wavelength region.

How do meteorologists predict the weather?

Computer Models

Weather and climate prediction require models of the earth-atmosphere system.

Computer Models

• A model is a computer program that represents the predictive equations that describe weather variables.

• What does a weather model look like? www.weather.unisys.com

• What variables do they describe?

Computer Models

Equations can predict because- they describe the change in time of a variable.These equations do this in terms of the forces involved that may change the variable and the advection of different properties by the wind.

Advection• Wind is bringing in warmer

temps

WARM AIR

Computer Models

http://climateprediction.net/images/sci_images/verticalres.jpg

Weather and Climate models use horizontal and vertical grids.

The equations are solved at each grid intersection.

http://www.research.noaa.gov/climate/images/modeling_schematic.gif

Computer Models

• Horizontal grid spacing for weather forecast models is quite variable but ranges between 10-50 km. Weather forecast models typically have 20-50 vertical levels.

• Climate models have much coarser grids with horizontal spacing of hundreds of km and just 10-20 vertical levels.

Weather and Climate models are different from one another in other ways:

1. The goals of the prediction are different.

Weather forecasts need to be accurate in an absolute sense – I.e. yes it will rain tomorrow.

Climate predictions usually are trying to determine change – I. e. the climate will warm 2 degrees. (Show calculations)

Weather and Climate models are different from one another in other ways:

2.What weather models can assume unimportant is often quite important for climate models.

The ocean temperature, for instance can assume to be constant for weather prediction but becomes very important to climate predictions.

Meteo 1020 Lecture 3Weather and Climate

The coarse grid of climate models requires that many physical processes important to climate must be represented approximately (parameterized).

An example would be a thunderstorm system that is 50 km wide. A weather model could predict this accurately with a 10 km horizontal grid.

For a climate model with a 200 km grid, this thunderstorm exists at a scale too small to resolve and its affects will not be represented unless a parameterization is developed to approximate it.

Poorly developed parameterizations are THE LEADING CAUSE of climate model error!

Meteo 1020 Lecture 3Weather and Climate

Model error (both climate and weather prediction) also arise from other sources:

1. Poor initial conditions – this is often due to bad data. Consider the importance of far off observations to the 7 day forecasts given that weather disturbances can travel hundreds of kilometers in day!

2. Predictability – due to nonlinearity (advection of the wind by the wind), our ability to predict the atmosphere, even with perfect observations, is limited. A certain amount of Chaos exists in the system that effectively limits absolute predictions of the atmospheric state.

Meteo 1020 Lecture 3Weather and Climate

The hydrologic cycle refers to the set of physical processes that redistribute water in its three phases (gas, liquid, and solid) within the earth system.

The following three points are quite important:

• Understanding the hydrologic cycle is of utmost importance in understanding climate!

• Recall the primary greenhouse gas is NOT carbon dioxide but water vapor!

• The parameterization errors that lead to uncertain climate predictions are primarily due to many of the physical process that compose the hydrologic cycle.

Meteo 1020 Lecture 3Weather and Climate

The law of conservation of mass applied to water in the earth system- For most purposes the mass of water is fixed so the rate of change of total water mass is zero.

With this understanding, we can write a predictive equation that tracks water through its various phases in terms of sources, sinks and storage.

The physical processes surrounding the phase changes of water are key to understanding the hydrologic cycle:

1. Saturation vapor pressure is a strong function of temperature2. Increasing energy is required for a water molecule to move from

solid to liquid to gas.

Meteo 1020 Lecture 3Weather and Climate

Conservation of energy applies: The energy required to evaporate a water molecule is released as heat when the molecule condenses.

This source of heat (the latent heat of condensation) is a critical energy source for the atmosphere.

• Latent heat drives thunderstorms development

• energy in the form of latent heat is transported from the tropical oceans to the higher latitudes on air currents. The energy is released when the water condenses to form clouds and precipitation.

• The image on the following page illustrates the poleward transport of water vapor. The white areas are clouds while the gray areas are composed primarily of upper tropospheric water vapor

Sunlight that Enters our Atmosphere

Weather vs. Climate

Weather• Characterized by

change– Time Scale-

• Hour to hour• Day to night• Month to Month

Climate– Time Average– Variance

• Defined by the extremes of weather

– Used to describe how the system works on long time frames

Weather vs. Climate

• Weather

–Time Scale-• Hour to hour

• Day to night

• Month to Month