Chapter 3 Temperature Dry Adiabatic Lapse Rate Environmental Lapse Rate Growing Degree Day GDD Heating Degree Day HGG Insolation Isotherm Lag Lapse Rate Monthly Mean Temperature Nocturnal Inversion Normal Temperatures Radiation Inversion Seasonal Temperature Cycle Statically Stable Atmosphere Surface Temperature Temperature Inversion Temperature Gradient Temperature Range Turbulence Wind Chill Temperature Key Terms Absolutely Unstable Adiabatic Process Annual Average Temperature Annual Temperature Range Anomalies Aspect Cooling Degree Day CDD Daily Mean Temperature Diurnal Temperature Cycle Diurnal Temperature Range Summary Temperature near the surface is governed by the energy gains and losses at ground level The ground gains energy during the day from the Sun and emits longwave radiation both day and night An imbalance between the gains and losses causes a change in temperature The surface exchanges with the air in a variety of ways Conduction between the ground and the atmosphere is slow and only affect the air temperature close to the ground Convection turbulent mixing by the winds and radiative and latent heat fluxes exchange most of the energy between the ground and the rest of the air If energy gains and losses ebb and flow in a regular pattern over time then the surface temperature will change in a cyclical pattern The surface temperature has cycles daily annual and interannual time scales The annual and diurnal temperature cycles are primarily driven by the periodic nature of solar energy gains at the ground The diurnal and annual temperature cycles are related to the following 1 Solar energy input and therefore latitude the time of day and time of year 2 The surface type including proximity to bodies of water which determines albedo and specific heat and influences evaporation 3 Advection a steady wind direction which can advect warm or cold air into a region 4 Cloud cover which suppresses temperature changes 5 Altitude and aspect which cause generally cooler temperatures at higher altitudes and on north facing slopes in the Northern Hemisphere Temperature changes with altitude above the Earth s surface The dry adiabatic lapse rate of 10 degrees Celsius per kilometer describes how the temperature of an air parcel changes as it goes up or down The environmental lapse rate describes how the temperature the temperature varies with altitude at a given time and location Comparing these two lapse rates allows us to know if an air parcel will keep rising If the environmental lapse rate is bigger than the dry adiabatic lapse rate the parcel will keep rising This situation is called absolutely unstable If the environmental lapse rate is less than the dry adiabatic lapse rate of 10 degrees km than the atmosphere is stable An extreme case of this is a temperature inversion when warmer air overlies colder air Vertical motions of air parcels are inhibited by these stable temperature inversions This is an example of an absolutely stable atmosphere Conditions favorable for the formation of a near surface temperature inversion are clear skies long nights calm and light winds and little vegetation These conditions promote radiative energy losses that are greatest neat the surface Drainage of cold air into valleys can also form inversions near the ground Temperature inversions play a role in air pollution episodes and agriculture During winter in the northern United States and Canada nightly weather reports often include wind chill equivalent temperature The wind chill temperature indicates how cold it feels outside as a result of the combination of surface temperature and wind Temperature indices are used to help predict agricultural and energy consumption needs Growing degree days are used to predict when a given crop will reach maturity Heating and cooling degree days are indicators of a building energy demand for heating and cooling respectively
View Full Document
Unlocking...