Heat, heat transport and weather EOS 365 Lecture 4 Spring 2013 Heat, heat transport and weather

= no motion of molecules Temperature and Heat Kinetic energy = 1/2 mv2 Heat: The total kinetic energy of the atoms/molecules making up some substance Temperature: A measure of the average kinetic energy of the individual atoms/molecules making up the same substance Temperature Units Celsius (oC), Fahrenheit (oF) or Kelvin (K): K = °C + 273.15 °C = K – 273.15 °C = 5/9 × (°F – 32°) °F = (9/5 × °C) + 32° 0 K = –273.2 °C = –459.7 °F = no motion of molecules

Heat Units Transport of Heat Calorie: Amount of heat required to raise the temperature of 1 gram of water from 14.5 °C to 15.5°C (not used much now) Joule: 1 Joule = (kg m2)/s2 = Force {kg m/s2} × Distance {m} 1 Joule = 0.2389 calories 1 calorie = 4.1868 Joules Transport of Heat Temperature Gradient: A change in temperature with distance e.g. Equator (warm) to Pole (cold) e.g. Earth's surface (warm) to Tropopause (cold) Heat always flows from hot to cold e.g. via: Conduction Convection Advection Radiation

Conduction Conduction occurs within a substance or between substances that are in direct physical contact Kinetic energy of atoms/molecules (heat) is transferred by collisions between neighbouring atoms or molecules Different substances conduct heat differently (i.e., more or less readily) e.g. styrofoam cup, metal spoon + hot coffee e.g. new, thick snow, vs. old, packed snow. Heat is conducted from warm Earth's surface to the overlying air. Air is not a very good conductor Conduction is only significant in a very thin layer of air in immediate contact with the Earth's surface

Convection Conduction + Convection = Sensible Heating Much more important and effective than conduction in transporting heat vertically in the the troposphere. Convection is the transport of heat within a fluid via motion of the fluid itself. In Meteorology and Oceanography, the term is usually applied to the vertical transfer of heat. Convection in the atmosphere: Conduction from the ground to the overlying air:  Warms overlying air Warmed air rises, colder air sinks process repeats Conduction + Convection = Sensible Heating sensible since heating can be felt or sensed as temperature changes directly

Advection: The horizontal transport of heat by the winds Radiation: Already discussed

 water said to possess: Specific Heat Specific Heat: The amount of heat required to change the temperature of 1 gram of a substance by 1°C. Substance Specific Heat Water 1.000 Ice at 0°C 0.478 Wood 0.420 Aluminum 0.214 Sand 0.188 Dry Air 0.171 Copper 0.093 Silver 0.056 Gold 0.031 Note: Five times more heat required to raise water by 1°C than sand by 1°C. High specific heat of water:  surface temperature of land is more variable with time than that of a body of water  water said to possess: Thermal Stability Check out www.victoriaweather.ca

Implications for climate Air temperatures are regulated by the temperature of the surface over which the air resides. Maritime and Ultramaritime localities exhibit smaller seasonal variations than do subcontinental and continental localities. Index of Continentality At our latitudes: Winds tend to blow from west to east, so Maritime and Ultramaritime regions are generally in the west.

Climate is what you expect and Heat imbalances and weather Weather: The state of the atmosphere at some place and time described in terms of such variables as temperature, cloudiness, precipitation, and wind. Climate: Weather conditions at some locality averaged over a period of time. Climate = The statistics of weather Climate is what you expect and weather is what you get

Heat imbalances and weather Imbalances in rates of heating and cooling from one place to another within the atmosphere produce temperature gradients The atmosphere and ocean circulate and redistribute heat The Earth’s energy balance

The Earth’s energy balance Sensible Heating Latent Heating

Sensible and latent heating Sensible Heating: Sensible heating = conduction + convection Latent Heating: Latent heating is the movement or transfer of heat as a consequence of changes in the phase of water e.g. liquid  gas, gas  liquid, liquid  solid, solid  liquid, gas  solid, solid  gas Phase change of water from liquid to vapour can occur at any temperature

Latent heat loss from the Ocean

Heat Transport At high latitudes, the rate of infrared cooling exceeds the rate of solar radiational warming (averaged over the whole year) The opposite occurs at low latitudes. Q: Why don't the tropics continually warm and the midlatitude/polar regions continually cool? A: Poleward transport of heat by the atmospheric and oceanic circulation (including latent heat transport)

Temperature Gradients Weather Response to Heat Imbalances Solar radiation drives the entire air-sea-ice system In the atmosphere:  Imbalances in rates of radiational heating and cooling set up Temperature Gradients  Atmosphere responds to redistribute the heat, causing Weather Seasonality:  The need for heat redistribution varies with season  Atmospheric response and hence weather vary throughout the year e.g. Winter in North America: very strong temperature gradients from, say, the southern U.S. to northern Canada  Often get stronger storms, winds than in the summer.

The Controls of Temperature Radiational controls: Conditions that influence local radiation balance and hence local air temperature: 1. Time of day and year (solar altitude) Temperature as a function of month, Clevelandia, Amazon Basin, 4°N, 52°W Very little seasonal variation. Night/day variation larger than seasonal variation.

The Controls of Temperature Radiational controls: Conditions that influence local radiation balance and hence local air temperature: 2. Cloud cover

The Controls of Temperature Radiational controls: Conditions that influence local radiation balance and hence local air temperature: 3. Surface cover (albedo) or (specific heat) Astronaut photo of an area in eastern Bolivia

South Cascade Glacier, Washington 1928 2000

The Controls of Temperature Air mass controls:

Global Distribution of Temperature Temperature decreases poleward from the tropics

January global mean sea-level temperatures Isotherm – a line connecting places of equal temperature January Temperatures are adjusted to sea level

Global Distribution of Temperature Temperature decreases poleward from the tropics Isotherms exhibit a latitudinal shift with the seasons

January July

Global Distribution of Temperature Temperature decreases poleward from the tropics Isotherms exhibit a latitudinal shift with the seasons Warmest and coldest temperatures occur over land

January July

Global Distribution of Temperature Temperature decreases poleward from the tropics Isotherms exhibit a latitudinal shift with the seasons Warmest and coldest temperatures occur over land Southern hemisphere isotherms are straighter

July global mean sea-level temperatures Isotherm – a line connecting places of equal temperature July Temperatures are adjusted to sea level

Global Distribution of Temperature Temperature decreases poleward from the tropics Isotherms exhibit a latitudinal shift with the seasons Warmest and coldest temperatures occur over land Southern hemisphere isotherms are straighter Annual temperature range: Small near the equator Increases with latitude Greatest over the continents

Small changes over ocean Large changes over land January-July surface air temperature difference Small changes over ocean Large changes over land

The End