WEATHER & CLIMATE WEEK Instructor: Matt Letts UHall C850) Office Hours: Tuesday 13h30 – 15h00 INTRODUCTION TO GEOGRAPHY SESSION GOALS: Geography majors Learn about the fundamentals of meteorology to prepare you for Weather & Climate 2015 Non Geography majors Understand the atmosphere around you and interpret a surface weather map

WEATHER & CLIMATE WEEK CONTENTS 1.Our Energy Source - The Sun - Radiation Emission - What Causes Seasons? - Earths Radiation Balance 2. Weather vs. Climate - Weather & Climate Defined (p. 233) - Why Study Weather? 3. Atmospheric Circulation - Air Pressure is Everywhere (p ) - Forces Acting to Create Wind (p ) - Global Atmospheric Circulation (p )

WEATHER & CLIMATE WEEK CONTENTS 4.The Importance of Water Vapour - Specific & Relative Humidity - Vapour Pressure 5. Instability and Cloud Formation - Causes of Instability (p. 238) - Causes of Precipitation (p ) 6. Analysis of Surface Weather Maps - Understanding Weather Symbols (p. 244) - The Mid-latitude Cyclone (p ) Optional Reading:

Stefan-Boltzmann Law As the temperature of an object increases, more radiation is emitted each second Energy emitted = (T 0 ) 4

Wiens Displacement Law As the temperature of a body increases, so does the proportion of shorter wavelengths

See:

Day and Night (09h00 MDT, Oct 23, 2006)

Source: NOAA ABSORPTION K TO SPACE=31 L <K !! Heat transfer 7+24=31 ! Compensates for radiation imbalance at surface L =69 L TO SPACE= = =0

White snow Old snow Vegetation Light colour soil Dark colour soil0.10 Clouds Calm water 0.10 (midday)

7.5 cm Air Temperature ( C) Aug 18Aug 19Aug 21Aug 22, 2005Aug cm Air Temperatures at Lakeview Ridge, WLNP

Current weather conditions Cloudy Temp.:+7°C Pressure:101.8 kPa Visibility:48km Humidity:54% DewPoint:-1°C Wind:WNW 26 km/h 09h00 October 23,

Thermometer (thermister) held within a Gill Radiation Shield SENSIBLE HEAT Radiation Sensors (PAR and K ) Raingauge Datalogger

Hurricane Katrina (August 29, 2005)

Lethbridge, Alberta

Photo: CBC

Photos: National Snow and Ice Data Center

Upsala Glacier, Argentina

Source: IPCC

WeatherClimate a) air temperature Long term averages b) atmospheric pressure of weather (eg. 30 y) c) humidity d) clouds Means e) precipitation Extremes f) visibilityVariability g) wind

LETHBRIDGE, ABVANCOUVER, BC

Source: Ahrens (1994)

Source: Solomon, 2000

HL km Pressure Gradient Force= 2.4 kPa / 600 km = 0.4 kPa / 100 km Definition: The difference in atmospheric pressure per unit distance PGF acts at right angles to isobars of equal pressure

Dont try this at home

Where are winds strongest ? Oct 18, 2004 Solution: HUDSON BAY Check the spacing of the isobars of equal surface pressure

Source: NASA

Surface roughness decreases wind speed Reduces impact of Inertial Coriolis Force Winds cross isobars, spiralling out of ANTICYCLONES (H), and into CYCLONES (L) H L

weather.unisys.com

H L Air tends to be unstable in low pressure (tendency to rise) Air tends to be stable in high pressure (tendency to fall)

1.Equatorial Low Pressure Trough 2.Subtropical High Pressure Cells 3.Subpolar Low Pressure Cells 4.Weak Polar High Pressure Cells

A ratio that compares the amount of water vapour in the air to the maximum water vapour capacity at that temperature The relative humidity of saturated air is 100% RH = [H 2 0 vapour content/H 2 0 capacity] x 100

The portion of atmospheric pressure that is made up of water vapour molecules (mb or kPa) SATURATION VAPOUR PRESSURE: The pressure that water vapour molecules would exert if the air were saturated (at a given temperature)

Absolute stability Temperature decreases with altitude more slowly than MALR (ELR > -6 C/km)

Temperature decreases with altitude more quickly than the DALR (ELR < -10 C /km)

VANCOUVERLETHBRIDGE 8°C8°C 12°C X X Cooling At MALR 6°C/km Warming At DALR 10 °C/km Cooling At DALR 10 °C/km Cooling At MALR 6°C/km Warming At DALR 10 °C/km More sensible heat

Cold advection Radiational cooling of clouds Solar heating of Earths surface Warm air advection at surface Air moving over a warm surface

See weather.unisys.com

SHARP COLD FRONT WARM, MOIST SOUTHERLY FLOW NORTH- EAST WINDS h GMT APRIL

GROWING DEGREE DAYS CORN HEAT UNITS Cumulative index of daily T avg < 18 C Cumulative index of daily T avg > 18 C Cumulative index of daily T avg > 4 C Cumulative index of daily T avg > 10 C