GEO 1130 Unit 2: Air Pressure, Atmospheric Circulation, Air Masses, Fronts, and Weather Forecasting

Comprehensive question-and-answer flashcards covering all major concepts, terms, models, instruments, and classifications from GEO 1130 Study Guide Unit 2.

How does air pressure change with height above Earth's surface?

Air pressure decreases continuously with increasing height above the surface because fewer air molecules are found at higher altitudes.

What is the pressure gradient force?

The force that arises from spatial differences in atmospheric pressure, causing air to move from areas of higher pressure toward areas of lower pressure.

Which three instruments are listed in the study guide for measuring air pressure?

The mercury barometer, aneroid barometer, and barograph.

How does station pressure differ from sea-level pressure?

Station pressure is the actual atmospheric pressure measured at the elevation of the observing station, whereas sea-level pressure is adjusted to mean sea level to allow direct comparison between stations at different altitudes.

What are isobars, contour lines, and isotherms?

Isobars connect lines of equal pressure, contour lines connect lines of equal elevation or height on upper-air charts, and isotherms connect lines of equal temperature.

How does the Coriolis effect impact wind in the Northern and Southern Hemispheres?

Due to Earth's rotation, the Coriolis effect deflects moving air to the right of its intended path in the Northern Hemisphere and to the left in the Southern Hemisphere.

What is a geostrophic wind?

A theoretical wind that blows parallel to straight isobars or height contours when there is an exact balance between the horizontal pressure gradient force and the Coriolis force.

How do cyclonic flow and anticyclonic flow differ?

Cyclonic flow circulates around a low-pressure center (counterclockwise in the Northern Hemisphere), while anticyclonic flow circulates around a high-pressure center (clockwise in the Northern Hemisphere).

What is the difference between meridional and zonal wind patterns on upper-level charts?

Zonal wind patterns flow predominantly west-to-east parallel to lines of latitude, whereas meridional wind patterns feature pronounced north-to-south loops and ridges across latitudes.

What vertical movement of air is produced by surface convergence versus surface divergence?

Surface convergence forces air together, leading to rising motion (vertical ascent), while surface divergence forces air outward, drawing sinking air downward (subsidence).

Which instruments are listed for measuring wind direction and speed?

Anemometer, wind vane, aerovane (skyvane), sonic anemometer, Rawinsonde observations, and satellites.

What are the three primary scales of atmospheric motion?

Microscale, mesoscale, and macroscale.

What causes thermal circulations like sea/land breezes and mountain/valley breezes?

Differential heating of adjacent surfaces that generates localized horizontal temperature and pressure gradients.

What are katabatic, Chinook, and Santa Ana winds?

Katabatic winds are cold downslope winds; Chinook winds are warm, dry winds descending the leeward slopes of mountains; and Santa Ana winds are warm, dry, gusty downslope winds affecting Southern California.

What desert winds are highlighted in the study guide, and how do haboobs form?

Haboobs and dust devils; haboobs form when downdrafts from a thunderstorm reach the ground and sweep desert dust and sand into a massive, surging wall.

Which two monsoon wind systems are identified in the study guide?

The Indian monsoon and the North American monsoon.

What are the three major convection cells in the three-cell model of global circulation?

The Hadley cell, Ferrel cell, and Polar cell.

What are the three major surface wind belts of the three-cell model?

The trade winds, westerlies, and polar easterlies.

What is the Intertropical Convergence Zone (ITCZ), and how does it move seasonally?

The ITCZ is the equatorial zone of low pressure and convergence between the northeast and southeast trade winds; it migrates north during the Northern Hemisphere summer and south during the Northern Hemisphere winter.

Which semipermanent pressure systems are listed in the realistic global circulation model?

The Bermuda High, Pacific High, Icelandic Low, and Aleution Low.

Which non-semipermanent pressure systems are identified in the notes?

The Siberian High and Canadian High.

What are the global precipitation patterns associated with pressure systems?

High precipitation occurs at the equatorial low and subpolar low, while low precipitation occurs at the subtropical high and polar high.

What are the two major jet streams discussed in the study guide?

The Polar jet and the Subtropical jet.

What factors govern major surface ocean currents?

Major wind belts, the distribution of continents, the Coriolis effect, and Ekman transport.

How do western boundary currents compare to eastern boundary currents?

Western boundary currents are warm, fast, narrow, and deep, whereas eastern boundary currents are cold, slow, broad, and shallow.

What causes equatorial upwelling versus downwelling in the ocean?

Diverging currents lead to equatorial upwelling (bringing cold, nutrient-rich water to the surface), while converging currents lead to downwelling (sinking surface water).

What is the economic importance of the Peru current highlighted in the notes?

It drives coastal upwelling that supports a highly productive marine ecosystem vital to the fishing industry.

What are the Walker circulation and Southern Oscillation?

The Walker circulation is the east-west atmospheric circulation cell driven by pressure differences across the tropical Pacific; the Southern Oscillation is the seesaw reversal of surface pressure between the eastern and western tropical Pacific.

What array is used to monitor El Niño Southern Oscillation (ENSO) events?

The TAO (Tropical Atmosphere Ocean) moored buoy array.

What natural oscillations besides ENSO are listed in the ocean-atmosphere interactions section?

The Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO).

How are air masses classified according to moisture and temperature?

By moisture: continental (dry) and maritime (moist); and by temperature: arctic (extremely cold), polar (cold), and tropical (warm).

How does lake-effect snow develop in North America?

When cold continental Polar (cP) or continental Arctic (cA) air masses pass over the relatively warmer, unfrozen waters of the Great Lakes, absorbing warmth and moisture before dropping heavy snow on downwind shores.

What is Pacific air?

Maritime Polar (mP) air from the Pacific that undergoes orographic lifting over western mountain ranges, losing much of its moisture before moderating into a milder, drier continental-like air mass east of the mountains.

What role do Maritime Tropical air masses play in North America?

They supply warm, highly humid air and are responsible for atmospheric rivers that channel narrow bands of intense water vapor and heavy precipitation.

What is a dryline?

A narrow boundary that separates a warm, moist maritime Tropical (mT) air mass from a hot, dry continental Tropical (cT) air mass, frequently serving as a focus for thunderstorm development.

What is an occluded front, and what are its two classifications?

A front that forms when a rapidly moving cold front overtakes a warm front; it is classified as either a cold occlusion or a warm occlusion depending on the relative temperatures of the advancing and retreating air masses.

What theory describes the life cycle and structure of mid-latitude cyclones?

The Polar front theory.

What are the four primary locations where mid-latitude cyclones form in North America?

Alberta Clipper, Colorado Low, Gulf Low, and Hatteras Low.

What are Nor'easters?

Intense mid-latitude cyclones that track up the East Coast of North America, producing strong northeasterly winds, heavy coastal rain, and inland snow.

Which surface-based instruments are specified for land and water measurements in the notes?

Electrical resistance thermometers, Automated Surface Observing Systems (ASOS), thermistors and radiosondes, standard rain gauges, and tipping bucket rain gages.

Which three satellites are listed in the study guide for measuring temperature and precipitation?

TRMM, GPM, and CloudSat.

Which meteorological organizations are responsible for oversight and forecasting in the study guide?

The World Meteorological Organization (WMO) and the National Center for Environmental Prediction (NCEP)/National Weather Service (NWS).

What is the difference between a meteogram and a sounding?

A meteogram displays how surface weather variables change over time at a single location, whereas a sounding shows the vertical profile of temperature, dew point, and winds aloft at a given point in time.

What is a prognostic chart (prog)?

A computer-generated forecast map portraying expected atmospheric conditions, such as surface pressures or upper-air heights, at a specific future time.

What is an ensemble forecast?

A weather prediction method that runs multiple numerical model simulations with slightly altered initial conditions to assess forecast reliability and uncertainty.

How do persistence forecasts differ from steady-state (trend) forecasts?

A persistence forecast assumes tomorrow's weather will replicate today's, while a steady-state (trend) forecast assumes weather features will maintain their current speed and direction of motion.

How do the analog method and climatological forecasts predict weather?

The analog method matches current weather features to similar historical weather maps, while a climatological forecast relies strictly on long-term historical climate averages.

What are the standard time frames for weather forecasts from nowcast to long-range?

Nowcast covers the immediate $0-6$ hours; short-range spans up to roughly $48$ hours; medium-range covers $3$ to $8.5$ days; long-range extends beyond $8$ days; and seasonal outlooks span multiple months.

What is the distinction between a watch, a warning, and an advisory?

An advisory warns of inconvenient or nuisance weather; a watch signals that severe or hazardous conditions are possible; and a warning confirms that hazardous weather is imminent or already occurring.

What is the forecast funnel approach?

A structured forecasting process that starts with the broad hemispheric/planetary scale (upper-air charts), narrows to synoptic surface maps, and finally zooms in to mesoscale and local city-level conditions.