Thanks to Martha Remos

QUIZ RESULTS – Overal Scores

QUIZ RESULTS – Individual Questions

ESCI 106 – Weather and ESCI 106 – Weather and ClimateClimate

Lecture 3Lecture 3

9-1-20119-1-2011

Jennifer D. Small Jennifer D. Small

Weather Fact of the Day: September 1

2008: A flash flood engulfed 4 hikers as they were trekking along the banks of River Prieto-River Blanco NW of Naguabo, PR.

Two escaped the flood surge, but two were swept away to their deaths

~1.5 in of rain had fallen on parts of the El Yunque National Forest.

National Watches and Warnings

Temperature (from Chapter 2)

Temperature is a quantity that describes how warm or cold an object is.

It can also be described as: a measure of the

average kinetic energy of the atoms or molecules in a substance

Temperature (from Chapter 2)

Temperature video from online..

http://www.atmosedu.com/meteor/Animations/TemperatureMolecular.mov

Air Temperature –why it’s important

It’s the first thing we usually think about when we talk about “weather”

Temperatures vary on different time scalesSeasonally, daily and even

hourlyTemperatures vary all

over the globe, by quite a bit.

We use Isotherms the distribution of temperature over a large area.They are lines that connect points on a map that have the

same temperature

Isotherms

Isotherms make it easier to read and analyze weather maps

By looking at patterns of temperature (and pressure) you can determine weather conditions in the next few days.

Isotherms – Why do we care??

Isotherm a Simplified Example

Let’s do an example together!

Air Temperature

Maximum Temperature: 96

Minimum Temperature: 42

Daily Mean Temperature: (96 + 42)/2 = 69

Daily mean temperatureAverage of 24 hourly readingsAdding maximum and minimum

and dividing by two.

Example

Air Temperature

Daily Temperature RangeThe difference between the maximum and

minimum daily temperatures

Example

Maximum Temperature: 96

Minimum Temperature: 42

Daily Temperature Range: (96 - 42) = 54

Air TemperatureMonthly mean

temperatureAdding together the

daily means for each day of a month and then dividing by the number of days in that month

Example

February Daily

Mean Temperatures

Feb 1: 32 Feb 15: 40

Feb 2: 31 Feb 16: 42

Feb 3: 33 Feb 17: 45

Feb 4: 32 Feb 18: 47

Feb 5: 35 Feb 19: 47

Feb 6: 37 Feb 20: 52

Feb 7: 39 Feb 21: 51

Feb 8: 42 Feb 22: 53

Feb 9: 40 Feb 23: 55

Feb 10: 39 Feb 24: 58

Feb 11: 37 Feb 25: 54

Feb 12: 40 Feb 26: 53

Feb 13: 41 Feb 27: 52

Feb 14: 39 Feb 28: 50

Sum of Daily Means: 1216

Number of Days: 28

Monthly Temperature Mean: (1216/28) = 43.4

Air Temperature

Annual Mean TemperatureAdding together the monthly

means and dividing by 12

Example

Annual Means

January: 49

February: 47

March: 52

April: 60

May: 69

June: 75

July: 80

August:: 83

September: 76

October: 65

November: 58

December 52

Sum of Monthly Means: 766

Number of Months: 12

Annual Mean Temperature: (776/12) = 63.8

Air Temperature

Annual Temperature RangeThe difference between the

warmest and coldest monthly mean temperatures

Example

Warmest Monthly Mean Temperature: 95

Coldest Monthly Mean Temperature: 25Annual Temperature Range: (95 - 42) = 70

What controls air temperature?

Differential Heating of land and water Ocean Currents Altitude Geographic Position Cloud cover and albedo

Land and Ocean – Differential Heating

Different surfaces absorb, emit and reflect different amounts of energy.This causes variations in air above each

surface

Land and Ocean – Differential Heating

In general: Land HEATS more rapidly and to HIGHER temperatures than Water.

In general: Land COOLS more rapidly and to LOWER temperatures than Water.

Land and Ocean – Differential Heating

Variations over Land are GREATER than variations over the Ocean!!!

The land surface has more variety….TreesStreetsBuildingsFieldsHouses….

Ocean – Why is it more variable?

Surface temperature of water rises and falls slower than land

Water is highly mobile and mixes easily (think mixing red and blue dye… turns purple)

Daily changes are about 6 meters deep

Yearly ocean and deep lakes experience variations through a layer between 200-660 m thick!

Land – Why is this the case?

Heat does not penetrate deeply into soil or rock; it remains near the surface.

Rocks are not fluid… so no mixing

Daily temperature changes are seen only 10 cm down

Yearly temperature changes reach only 15 meters or less

Land and Ocean – Summer vs. Winter

During summer a thick layer of water is heated while only a thin layer of land is heated.

During winter the shallow layer of rock cools rapidly while the deeply heated water takes a longer time to cool. as surface water cools it becomes heavier and

sinks, replaced with warmer less dense water from below….This means the surface temperture of water doesn’t

appear to change much

Land and Ocean – opaque vs. transparent

Because land surfaces are opaque heat is absorbed only at the surface

Water is transparent and lets energy from the sun penetrate to a depth of several meters

Land and Ocean – Specific Heat

The specific heat (the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius) is greater (~3 times) for ocean than land.

The OCEANS require MORE heat to raise its temperature the same amount as an equal quantity (grams) of land.

Land and Ocean – Evaporation

Evaporation is greater from Oceans than from LandThere’s more water

molecules

Energy is required to evaporate water

When energy is used to evaporate water it is not available for heating.

WATER WARMS MORE SLOWLY THAN LAND!!

Class Question??

Which Hemisphere (north or south) has larger temperature variations?

Why??

The Northern Hemisphere has greater variations in temperature than the

Southern Hemisphere

There is more ocean than in the Southern Hemisphere. There is little land to interrupt

the oceanic and atmospheric circulation. Thus, the SH has smaller variations in

temperature.

Ocean Currents

Ocean currents are caused by wind (interactions between the atmosphere and ocean).

Energy passes from the atmosphere to the ocean via friction.The DRAG exerted be the wind

causes it to move

Ocean Currents

The transfer of heat by winds and ocean currents equalizes latitudinal energy imbalances

Ocean Currents – Poleward Currents

Warm water from the tropics travels up the coast via the Gulf Stream

It becomes the North Atlantic Drift and helps keep English and Irish weather mild.

GULF STREAM!

Have a MODERATING effect !!

Ocean Currents – Cold Currents

Predominately influence the tropics during summer months

Happen in regions of costal upwelling

Associated with cool summers and fog

CALIFORNIA CURRENT

Have a COOLING effect !!

Altitude

Atmospheric Lapse Rate: 6.5 C per km Cooler temperatures at greater heights

Altitude

However, additional heating of the LAND (e.g. Mountain) causes the temperature to be WARMER than predicted by the lapse rate

Absorbtion and reradiation of solar energy by the ground surface keep places like Quito, Ecuador warmer than expected

Altitude

Again, atmospheric pressure and density decreases too so it absorbs and reflect less solar radiation.

Geographic Position

Windward: prevailing winds blow From the Ocean to the SHORE

WIND DIRECTIO

N

WIND DIRECTION

Leeward: prevailing winds blow TOWARDS the Ocean

Lacks Ocean Influence, More like Land Temperatures

MORE VARIABLE TEMPERATURES

Moderated by the Ocean air, cool summers-mild winters

LESS VARIABLE TEMPERATURES

Cloud Cover and Albedo

Clouds cool during the dayHigh ALBEDOLower Maximum

Clouds warm at nightTrap OUTGOING

Longwave radiation Higher Minimum

WORLD DISTRIBUTION OF TEMPERATURES

Decrease in Temperature from Equator to Poles

Warm colors to Cool colors

JANUARY

JULY

WORLD DISTRIBUTION OF TEMPERATURES

Latitudinal Shifting due to the seasonal migration of the Sun.

“HOT SPOTS”Differential heating

Heating is largely a function of LATITUDE

JANUARY

JULY

WORLD DISTRIBUTION OF TEMPERATURES

The hottest andcoldest places areover land.

Warm oceancurrents moving tothe Poles warm theair.

Equatorialbound currentsHelp cool the air.

WORLD DISTRIBUTION OF TEMPERATURES

Equatorial temperaturesdo not fluctuate

significantly(there are no seasons).

Middle and higher latitudes

have much stronger seasonalsignals.

-40

25

25

-10

CYCLES of AIR TEMPERAUTRE

Daily Temperature VariationsMagnitude of Daily Temp Changes Depends on

Variations in Sun angle (location)Windward vs. leeward (location)Clouds or no clouds (weather)Amount of water vapor (weather)

Annual Temperature VariationsMonths with highest and lowest mean T do not

correspond to periods of max and min radiationShows that solar radiation isn’t the only thing governing

surface temperatures,

TEMPERATURE MEASUREMENT

Mechanical thermometersElectronic thermometersInstrument shelters

Mechanical Thermometers

Most substances EXPAND and CONTRACT as a function of temperature… Most thermometers use this principle.

Liquid-in-gas thermometersMost common in daily useMaximum ThermometersMinimum Thermometers

Mechanical Thermometers

Bimetal stripConsists of two thin strips of metal that

are bonded together and have different expansion properties causing it to bend and curl.

Mechanical Thermometers

ThermographUses a bimetal stripContinuously measures temperature as

the strip bends and flexes.

Pen records temperature on special paper.

Not as accurate as liquid-in-glass

Electric Thermometers

Thermistors are present in electric thermometersThermal resistorAs temperature increase so does

the resistance, reducing the currentAs temperature decreases, the

resistance decreases allowing current to increase

Instrument Shelters

Where you take temperature mattersInstrument Shelters are:

White – for high albedo (reduce solar heating)Ventilated – so it doesn’t get hot like your car1 meter high – reduce longwave heating

Temperature Scales

FahrenheitCelsiusKelvin

Fahrenheit

Fahrenheit is the temperature scale proposed in 1724 by, and named after, the Dutch-German-Polish physicist Daniel Gabriel Fahrenheit

Based on “Fixed Points” – coldest temperature he could measure and assumed human body temp.

That’s why Freezing is at 32 and Boiling is a 212.

Celsius

Invented by Swede Anders Celsius 28 years after Fahrenheit (1742)

Decimal Scale

0 degrees = Freezing

100 degrees = Melting

Kelvin

Also called the “Absolute Scale”

The Kelvin scale is named after the Belfast-born engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale".

Same Spacing as Celsius – 100 divisions between boiling and melting

0 K = the temperature at which all molecular motion is presumed to cease

Converting between temperature scales

To go from Fahrenheit to Celsius

°F = (1.8 X °C) + 32

To go from Celsius to Fahrenheit

°C = (°F – 32) / 1.8

Converting between temperature scales

To go from Celsius to Kelvin

K = ° C + 273.15

° C = K - 273.15

To go from Kelvin to Celsius

Converting between temperature scales

To go from Fahrenheit to Kelvin

K = (°F - 32) * 5/9 + 273.15

To go from Kelvin to Fahrenheit

°F = (K - 273.15) * 9/5 + 32

APPLICATIONS of TEMP DATA

Heating Degree-DaysWhen you turn the heat on

Cooling Degree-DaysWhen you turn the AC on

Growing Degree-DaysWhen plants can grow

Temperature and ComfortHow temperature ACTUALLY feels

Heating Degree-Days

Developed by Engineers in the early 20th century

A way to evaluate energy demandDon’t need the “heat” if it is 65F or

warmer outsideAny degree BELOW 65 counts as a

heating degree-daye.g. if it’s 50F out….

That’s 65-50 = 15 heating degree-days

Total it up for the whole year or season HEATING SEASON is defined as

July 1st through June 30

Cooling Degree-Days

Developed by Engineers in the early 20th century

A way to evaluate energy demand for cooling a building If its above 65 you need the AC on…. Any degree ABOVE 65 counts as a

Cooling degree-daye.g. if it’s 85F out….

That’s 85-65 = 20 cooling degree-days

Total it up for the whole year or season

COOLING SEASON is defined as January 1st through December

31st

Growing Degree-Days (GDDs)

Used by farmers to determine the approximate date to harvest their crops.SUPER HANDY here in CA

Specific for each CROP

The number of GDDs for a crop on any day is the difference between the daily mean temperature and the base temperature of the crop

Growing Degree-Days (GDDs)

Example:

Sweet Corn Base Temperature = 50 F

Peas Base Temperature = 40 F

If Mean Daily Temperature = 75 F

Sweet Corn GDDs = 75-50 = 25

Peas GDDs = 75-40 = 35

Thus, if 2000 GDDs are needed to mature a crop, you just keep track of when you reach

2000 GDDs and then harvest!

Growing Degree-Days (GDDs)

Temperature and Comfort

How we perceive temperature matters to us humans. It is affected by:Relative humidityWindSunshine

Heat IndexWhen it’s humid, evaporation doesn’t work as well and

we “Feel” hotter

WindchillWind makes it “Feel” colder than it actually is

Temperature and Comfort