Sebastian W. Hoch & C. David Whiteman

Atmos 3200/Geog 3280Mountain Weather and Climate

Mountain Climates

Snowpatch Spire, Bugaboos © CD Whiteman

Climate differs from one location to another because of four primary factors:• Latitude• Altitude• Continentality• Exposure to regional circulations,

including winds and ocean currents

Four main climate factors

Latitude determines length of day and angle of incoming sunlight and, thus, amount of solar radiation received.• In equatorial regions, day length & solar angle change

little with season. Little seasonal variability, mostly diurnal changes.

• In polar regions (NH), the sun does not rise at all in winter. In the summer it never sets, although remaining low in sky. Big seasonal changes, small diurnal changes.

• In mid-latitudes, seasonal and diurnal changes.

Latitude also determines site’s exposure to latitudinal belts of high and low pressure• High pressure - subsidence• Low pressure - convection

Latitude

Revolution of Earth around Sun

Ahrens (1994)Northern Hemisphere terminology

• Zonal, meridional (winds)• 360°/24 hours = 15°/hour• Plane of ecliptic• Obliquity of ecliptic = 23.5°• Aphelion• Perihelion• Eccentricity of earth’s orbit• Mean earth diameter = 6371 km

Winter solstice: Dec 21/22Vernal equinox: Mar 20/21Summer solstice: June 21/22Autumnal equinox: Sep 22/23

7% higher insolation on hemisphere in perihelion in summer!

Terminology

(2000)(2000)

Image Credit & Copyright: Ian Griffin (Otago Museum) https://apod.nasa.gov/apod/ap200109.html

Solar “constant”

Whiteman (2000)

Past and future eccentricity of Earth's orbit.

Past and future obliquity of Earth's orbit.

Past and future sin of angle "longitude of perihelion"

Wikimedia Commons

“Milankovitch cycles”

Sun diurnal path in the sky

Day length vs latitude

Sun at high latitude

Temperature: seasonal vs. diurnal changesdi

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seasonal change

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seasonal change

Mt Pangrango 3019 m7ºS

Zugspitze 2962 m47ºN

Barry (1992)

• Net radiation (incoming – outgoing) and temperature decrease as latitude increases.

• Elevation of treeline / snowline decreases poleward.

• Belt of alpine vegetation and permanent snow and ice are lower on mountains at high latitude versus the tropics.

Impacts of latitude

Snow lines and timberlines

• Air density and atmospheric pressure decrease exponentially with altitude.

• Incoming solar radiation increases with altitude.• Changes in air temperature at high altitudes are

small, however, because of smaller amount of land area at higher altitudes.

• Air temperature usually decreases with altitude (mean: -6.5°C/km).

• Moisture in air usually decreases with altitude.• Wind speed usually increases with altitude.

Altitude

Whiteman (2000)

Mesopause

Stratopause

Tropopause

Distribution of state variables (p,ρ,T,u) depends strongly on height in free atmosphere and as function of terrain height.

Vapor pressure of water and radiation also vary strongly with height.

Thermopause

• The degree to which a point on the earth’s surface is in all respects subject to the influence of a landmass. Compare oceanicity.

• Continental locations experience larger diurnal and seasonal temperature changes than locations on or near large bodies of water because land surfaces heat and cool more quickly than oceans.

• Interior locations experience more sunshine, less cloudiness, less moisture and less precipitation than coastal areas.

• Precipitation is especially heavy on the windward side of coastal mountain ranges oriented perpendicular to prevailing winds from the ocean. Marine air lifted up a mountain range releases much of its moisture as precipitation. As a result, far less precipitation is received on the leeward side.

Continentality

• Arises from differences in heat capacity and heat conductivity of soils vs. water

• Water able to store more heat• Soils store less heat

• Degree of continentality expressed by annual range of mean monthly temperatures

Continentality

Fairbanks, AK Nome, AK

http://www.usclimatedata.com/climate/

50ºF

10ºF

10ºC

-12ºC

FN

• Latitude, altitude and continentality are the primary factors, but exposure to regional winds and ocean currents is also a factor

• Some regional winds are associated with the latitudinal bands of high and low pressure (e.g., Pacific High, Aleutian Low, Bermuda-Azores High)

• Ocean currents also play an important role. Ex: Gulf Stream in Atlantic and Japanese Current in Pacific affect North America.

– The southern branch of the Japanese Current draws surface water away from the Pacific Coast, allowing much colder water from below to rise to the surface (“upwelling”), producing coastal fog and stratus clouds.

– Ocean currents turn somewhat to the right (NH) of the winds that drive them.

Regional circulations

Whiteman (2000)

Latitudinal distribution of highs and lows

Whiteman (2000)

Summer Winter

Seasonal changes in pressure patterns

• Mountain Climate– Barry, R. G., 1992: Mountain Weather and Climate, 2nd Edition.

Routledge, New York, 402 pp.

– Price, L. W., 1981: Mountains and Man: A Study of Process and Environment. University of California Press, Berkeley, 506 pp.

– Whiteman, C. D., 2000: Mountain Meteorology. Oxford University Press, New York, 355pp.

– Papineau, J., 2002: Mountain Weather The Complete Guide for Outdoorspeople. Tab Books, 192 pp.

– Woodmencey, J., 1998: Reading Weather. Where will you be when the Storm Hits? Falcon Press, 160 pp.

– Various field guide series of books on Weather.

• Solar Radiation:– Waugh, A. E., 1973: Sundials: Their Theory And Construction. New

York, Dover Publications, Inc. 228 pp.

Sources