Meteo 201 - Definitions

Temperature

a measure of the average kinetic energy of the molecules of a substance

Troposphere

the lowest layer of the atmosphere in which temperature decreases with height, on average

Boundary layer

lower part of the troposphere that is significantly affected by exchanges of energy, mositure and momentum with the ground

Stratosphere

the layer above the troposphere, stretching to ~50km

Tropopause

the boundary between the troposphere and the stratosphere

Inversion

an atmospheric layer in which temperature increases with height

Environmental lapse rate

the rate at which temperature decreases with height

Diurnal Range

difference between the highest and lowest temperature of a day

Seasonality

difference in temperature between the warmest and coldest months

Surface Station Model

a compact way on a map to show weather data observed at a particular location at a particular time

Anemometer

measures the speed of the wind

Wind Vane

point in the direction that air is coming from (ie. Wind direction)

Stream Lines

lines that are everywhere parallel to the wind direction at a particular time

Prevailing wind

the wind direction most frequently observed, on average, during a specified period (typically a month, or season, or annually)

Pressure

weight of air column, per unit area

Isopleth

a line of equal value of something

Gradient of Q

change in value of Q, distance over which change is measured

Tropical Cyclone

generic term for a low pressure system that forms over warm tropical seas and has an observable cyclonic circulation

Tropical depression

a tropical cyclone with maximum sustained winds of less than 39mph

Tropical storm

a tropical cyclone with maximum sustained winds of 39-73mph

Hurricane

a tropical cyclone with maximum sustained wind of at least 74 mph

Storm Surge

the rise in ocean level as a tropical cyclone makes landfall, caused by winds blowing ocean towards shore

Climatology

use the average (ie. the normal)i as the forecast

Persistence

what has happened will continue to happen

Analog Forecasting

assume weather repeats itself (almost)

Grid point model

cover the forecast area with a 3D-grid, solve equations as grid point

Spectral model

because atmospheric variables tend to be wavy, build a model using wavy mathmatical functions

initial conditions

the values of all the variables that are given to the model at the beginning of a run

Ensemble Forecasting

a set of computer model forecasts rather than just one

Plume diagrams

in general, the lines separate as the forecast goes farther out, indicating that the forecast is becoming more uncertain with time

Humidity

generic word used widely to describe moisture in atmosphere

Parcel

blob of air of various sizes

saturation

condition at which evaporation rate = condensation rate. when condensation rate > evaporation rate, condensation nuclei grow → clouds

Calorie

amount of energy required to raise temperature of one gram of water by 1ºC

latent heat

“hidden heat” hidden in molecules to get back if you reverse the process

Condensation nuclei

microscopic particles of dust, dirt, soot, salt, and other particles in air onto which water vapor condenses to form cloud drops

wet-bulb temperature

lowest temperature to which air can be cooled by evaporating water into it

dew-point

temperature to which air must be cooled at constant pressure for saturation to occur

hygrometer

instrument to measure moisture content of air

Planck’s law

all matter emits radiation constantly and at all wavelengths

Wien’s Law

matter does not emit radiation at all wavelengths equally. The hotter the object, the shorter the wavelength of maximum emission

stefan-boltzman law

the total energy emitted per unit area is proportional to the 4th power of temperature

kirchoffs law

an object that absorbs radiation efficiently at a particular wavelength will also emit radiation efficiently at that wavelength E=𝜎T⁴

Absorption

object heats and/or changes phase

transmission

radiation passes through object

back-scatter (reflect)

radiation emerges back toward the source

albedo

fraction of visible radiation back-scattered

conduction

molecular collisions transfer energy

convection

blobs (parcels) of rising air transfer energy

In-situ observations

instrument in direct contact with the medium it is measuring

remote obsercations

instrument not in direct contact with the medium its measuring