THE ENERGY BALANCE AT SURFACE Net Radiation + Sensible Heat + Latent Heat + Ground Heating = 0 1 st LAW OF THERMODYNAMICS (CONSERVATION OF ENERGY): Energy only changes from one form to another. It cannot be created or destroyed. Read pages 49, Book

SENSIBLE AND LATENT HEAT STATES OF MATTER Gas: The particles move rapidly; there are larger spaces between them Liquid: The particles move less rapidly; they are closer Solid: The particles move very little and are arranged in a tight pattern Gas LiquidSolid

SENSIBLE AND LATENT HEAT HEAT TRANSFER: Radiation: electromagnetic waves transport energy trough space (e.g. sun radiation) Conduction: the transfer of energy trough matter from particle to particle. Convection: the transfer of heat by mass motion of a fluid (water, air) when the heated fluid is caused to move away from the source of heat (the heated fluid is less dense and rises)

SENSIBLE HEAT: Heat sensed by touching or feeling (measured by a thermometer) Sensible heat transfer (Ex: conduction, convection) LATENT HEAT: Hidden heat. It’s stored in the form of a molecular motion when a substance change from solid to liquid, liquid to gas, or solid to gas Latent heat transfer: when water evaporates from a moist surface or water surface it removes the heat stored in the change of state (transference of heat from surface to atmosphere) cooling surface

SENSIBLE HEAT LATENT HEAT

SURFACE AND AIR TEMPERATURE TEMPERATURE: Temperature is the measure of level of sensible heat of matter (gaseous, liquid, solid) SURFACE TEMPERATURE: Temperature in a surface is determined by the balance among various energy flows: Net radiation (positive at day, negative at night) Sensible heat transfer Conduction: from warm to cold trough direct contact (ex: heat into soils) Convection: fluid is heated by warm surface, expand, rises (upward flow) Latent heat transfer:when water evaporates at a surface, it removes heat stored (cooling surface). When condenses at surface, latent heat is released (warming surface)

THE AIR TEMPERATURE (CHAPTER 3 BOOK) Temperature observed at short distance above surface (1.2m or 4 feet) Air temperature and surface temperature can be different, but air temperatures tend to follow surface temperatures (because of heat flows) Weather information uses air temperature

AIR TEMPERATURE MEASUREMENT In US is widely measured using Farenheit The Celsius scale is the international standard The World Meteorological Organization (WMO) is a specialized agency of United Nations. One of its purposes is to promote standardization of meteorological observations Instrument used: Thermometer liquid-filled (expands when liquid is heated, contracts when is cooled) thermistor (change of electrical resistance with temperature)

Mongolia (Midlatitude) Baltimore (Midlatitude) Min: 6.0 F Max: 60.0 F Min: 45.0 F Max: 65.0 F Not always temperature at same latitudes are similar, for example:

TEMPERATURE RANGE Daily: Tmax- Tmin Annual: Difference between the lowest and highest monthly mean temperatures

THE AIR TEMPERATURE The factors that influence air temperature are: 1.Insolation 2. Latitude 3. Surface type (urban, moist soil, forest, deserts) 4. Coastal vs interior location: Narrower range of air temperatures in coast (water heats and cools more slowly than land) 5. Elevation

ANNUAL CYCLE OF MAXIMUM AIR TEMPERATURE (SOUTHERN HEMISPHERE) SS EE In-class Exercise

URBAN-RURAL DIFFERENCES RURAL: vegetation transpiration cooler surface moist soil evaporation URBAN: dry surfaceinsolationwarmer surface asphalt and roofing (dark surfaces) more absorption (twice the vegetation) warmer surface

LAND AND WATER CONTRASTS The range of temperature is lower in water Continental air temperature isotherms shift over a much wider latitude range from summer to winter than oceanic air temperature isotherms.

Reasons: 1. Penetration vs no penetration of radiation 2. Water heats and cools slowly than land 3. Mixing (warm and cool water) vs no mixing 4. More evaporation vs less evaporation LAND AND WATER CONTRASTS 1. penetration 1.No penetration 2.Land heats quickly 3.mixing 3. No mixing 2. Water heats slowly 4. More evaporation 4. Less evaporation

HIGH-MOUNTAIN ENVIRONMENTS

DAILY CYCLE OF AIR TEMPERATURE During day: net radiation is positive During night: is negative surface gains heat surface loses heat Location at 45°N Why minimum temperature takes place in early morning and not during the night? Factors: Earth’s rotation on its axis, latitude, urban/rural, elevation In-class Exercise

During night: NEGATIVE net radiation heat flows from ground surface surface air layer warms a little bit, but remains with low temperatures Ground surface is cooled Surface air layer is cooled Lower temp Lower temp… Until net radiation is POSITIVE