Atmospheric Moisture, Clouds, Stability, and Air Pressure

Vocabulary practice flashcards covering atmospheric humidity, fog and cloud classification, satellite meteorology, lapse rates and stability, precipitation processes, and atmospheric pressure and wind dynamics.

Hydrologic Cycle

The unending circulation of Earth's water supply, in which precipitation exceeds evaporation over land, evaporation exceeds precipitation over the oceans, and runoff compensates for the difference.

Vapor Pressure

The part of the total atmospheric pressure exerted by water vapor molecules, expressed in millibars ($\text{mb}$).

Saturation (Atmospheric)

The state that occurs when the air holds as much water vapor as it physically can at a given temperature, where warm air can hold more water vapor than cold air.

Saturation Vapor Pressure

The portion of total atmospheric pressure exerted by water vapor molecules in saturated air ($\text{mb}$), which is temperature dependent and obtained from a reference chart.

Mixing Ratio

A measure of humidity defined as the weight of water vapor per weight of dry air, expressed in grams per kilogram ($\text{g/kg}$).

Saturation Mixing Ratio

The weight of water vapor per weight of saturated air, expressed in grams per kilogram ($\text{g/kg}$).

Relative Humidity

The ratio of actual water vapor content (mixing ratio) to the saturation mixing ratio, simplified as a fraction and expressed as a percentage.

Dew Point Temperature

The temperature to which air must be cooled in order to reach saturation ($100\%$ relative humidity).

Sling Psychrometer

An instrument used to calculate dew point temperature and relative humidity based on the difference between dry-bulb and wet-bulb temperatures, where a smaller difference indicates higher relative humidity.

Dew

Liquid water droplets formed by condensation on surfaces during clear, calm nights when the surface temperature is greater than $32^\circ\text{F}$.

Frost

Ice crystals formed on surfaces by deposition directly from water vapor on clear, calm nights when temperatures are below $32^\circ\text{F}$.

Radiation Fog

A fog formed through cooling when warm, humid air cools after sunset; it is common in valleys and characterized in Florida by calm winds and patchy coverage.

Advection Fog

A thick, dense fog formed when warm, humid air moves horizontally across a colder surface and drops in temperature to its condensation point.

Upslope Fog

Fog that develops when warm, humid air moves up mountain terrain and cools to its condensation temperature as it ascends.

Precipitation Fog

An evaporation-induced fog formed when falling raindrops evaporate into the air, which then cools to saturation after sunset or as colder air moves in.

Steam Fog

A fog formed through evaporation that always develops over water when lake water evaporates and recondenses as cooler air moves over the warmer lake.

Cumulus

Puffy, fair-weather clouds with flat bottoms and big cotton-ball tops formed by rising air, which can grow vertically into cumulonimbus clouds.

Stratus

Layered, featureless low clouds that form an overcast veil or sheet without distinct individual shape when warm, moist air cools.

Cirrus

Wispy and thin high-level clouds composed entirely of ice crystals formed from supercooled water droplets.

Clouds of Vertical Development

Clouds such as cumulonimbus that have bases in low atmospheric levels and tops extending to high altitudes as high as $60{,}000\,\text{feet}$, releasing energy as thunder and lightning.

Geostationary Satellite

A weather satellite placed in orbit at an altitude of $22{,}300\,\text{miles}$ ($36{,}000\,\text{km}$) that moves at the same speed as Earth's rotation to continuously monitor storms.

Polar-Orbiting Satellite

A weather satellite orbiting at an altitude of approximately $500\,\text{miles}$ ($879\,\text{km}$) that travels from pole to pole, photographing data-sparse regions twice daily for complete Earth coverage.

Infrared Satellite Imagery

Satellite imagery available $24\,\text{hours/day}$ across $256$ levels, displaying low-level warm non-precipitating clouds as gray and high-level cold precipitating clouds as white.

Visible Satellite Imagery

High-resolution satellite imagery available only during daylight hours, where all clouds appear white and individual cloud formations can be resolved.

Adiabatic Temperature Change

A temperature change occurring within an air parcel resulting purely from expansion (cooling) or compression (heating) without the addition or subtraction of heat.

Dry Adiabatic Lapse Rate

The rate at which unsaturated air cools as it ascends or warms as it descends, equal to exactly $10^\circ\text{C/km}$.

Wet Adiabatic Lapse Rate

The rate at which saturated rising air cools, equal to $5^\circ\text{C/km}$, which is slower than the dry rate because the condensation of water vapor releases latent heat that offsets cooling.

Absolute Instability

An atmospheric condition in which the environmental lapse rate is greater than the dry adiabatic lapse rate ($> 10^\circ\text{C/km}$), causing lifted air parcels to remain warmer than their surroundings and continuously rise.

Absolute Stability

An atmospheric condition in which the environmental lapse rate is less than the wet adiabatic lapse rate ($< 5^\circ\text{C/km}$), causing lifted air parcels to be colder than their surroundings and sink back to their starting altitude.

Conditional Instability

An atmospheric state where the environmental lapse rate lies between $5^\circ\text{C/km}$ and $10^\circ\text{C/km}$, making the atmosphere unstable for saturated air parcels and stable for unsaturated air parcels.

Subsidence

The downward sinking of a column of air, which causes compression, warming, rising pressure, falling relative humidity, and fair, sunny weather.

Lake-Effect Snow

Heavy localized snow produced when cold air moves across a warmer body of open lake water, picking up moisture and destabilizing the air mass.

Condensation Nuclei

Microscopic solid surfaces measuring approximately $1\,\mu\text{m}$ (such as dust, smoke, pollen, or salt) onto which water vapor molecules ($0.0001\,\mu\text{m}$) condense.

Collision-Coalescence Process

A mechanism of raindrop formation in warm clouds where liquid water droplets with opposite charges collide and merge, requiring approximately $1\text{ million}$ collisions to produce a single raindrop.

Bergeron Process

A precipitation-generating mechanism in cold clouds where ice crystals grow at the expense of surrounding supercooled water droplets, capable of producing all precipitation types.

Supercooled Water Droplets

Liquid water droplets that remain unfrozen at temperatures below freezing ($< 32^\circ\text{F}$) and freeze upon contact with surfaces or ice crystals.

Sleet

A solid winter precipitation type consisting of ice pellets formed when snowflakes melt in a warm air layer and subsequently refreeze before striking the ground.

Freezing Rain

A winter precipitation type where snowflakes melt into liquid drops, become supercooled as they pass through cold air, and freeze immediately upon contact with surface objects.

Hail

Solid, layered precipitation formed in spring thunderstorms via the Bergeron process as ice particles grow while circulating through convective updrafts until becoming too heavy to remain suspended.

Standard Rain Gauge

A precipitation-measuring instrument accurate to $0.01\,\text{in}$ with a total capacity of $11\,\text{in}$, using an inner tube with $\frac{1}{10}$ the area of the collecting funnel, where $1\,\text{in}$ of liquid water equals $10\,\text{in}$ of snow.

Air Pressure

The force exerted on every atmospheric surface resulting from the molecular collisions of gas particles.

Barometer

An instrument that measures atmospheric pressure, where standard pressure at sea level is $29.92\,\text{in}$ of mercury ($1013.25\,\text{mb}$ or $14.7\,\text{lbs/in}^2$).

Pressure Gradient Force (PGF)

The fundamental force driving wind produced by differential surface heating, which directs air from areas of high pressure toward areas of low pressure.

Coriolis Effect

An apparent deflective force caused by Earth's rotation that deflects air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, acting at right angles to wind direction as a function of wind speed and latitude.

Centrifugal Force

An apparent outward-directed force in curved atmospheric flow that depends directly on wind speed.

Geostrophic Wind

An upper-level wind produced by a balance between the pressure gradient force and the Coriolis force, blowing parallel to straight isobars in the absence of friction.

Anticyclone

A high-pressure system characterized by sinking, stable air that diverges outward at the surface and rotates clockwise in the Northern Hemisphere, accompanied by warming temperatures and decreasing relative humidity.

Cyclone

A low-pressure system characterized by rising, unstable air that converges inward at the surface and rotates counter-clockwise in the Northern Hemisphere, accompanied by cooling temperatures and increasing relative humidity.

Wind Vane

A meteorological instrument designed to determine wind direction by pointing directly into the oncoming wind.

Cup Anemometer

A meteorological instrument featuring rotating hemispherical cups used to measure wind speed.