SEASONAL ATMOSPHERIC CIRCULATION WESTERN NORTH AMERICA


Sheppard 2002

REGIONAL CLIMATE

WINTER: Aleutian Low brings cyclonic storms into the West from the Pacific Ocean. As winter progresses, the Low intensifies and moves southward.

EARLY WINTER (Dec, Jan), high pressure cell (winter monsoon) prevents storms from entering the Great Basin.

EARLY SPRING (Mar, Apr): high pressure cell weakens, storms to enter the northern Great Basin from the Pacific Ocean. Centered in N Nevada "Tonopah Low"

SUMMER: the Pacific and Bermuda Highs intensify and move northwest-ward
LATE SUMMER: Tropical Storms may bring catastropic precipitation to the Southwestn


Tonopah Low

1983 flood


CLIMATIC REGIONS: Equivalent Potential Temperature

Boundaries and wind-flow patterns follow major topographic features Pyke, 1972; Mitchell, 1976

SEASONAL ATMOSPHERIC CIRCULATION DURING THE Insolation Maximum 12 to 9,000 ya (Northern Hemisphere ):

Increased summer temperatures increased stability of east Pacific High, and increased evaporation, producing an
    "EARLY HOLOCENE XEROTHERMIC" in the Pacific Northwest. Hebda & Matthews (1984), Clague & Mathewes (1989), Barnosky (1984), (Davis et al., 1984), (Davis et al., 1985)

    Greater summer contrast (cooler ocean, warmer land), and enhanced circulation around the Bermuda High increased monsoonal precipitation, producing higher lake levels and an

    "EARLY HOLOCENE PLUVIAL" Oviatt (1988), Spaulding and Graumlich (1986), Davis and Sellers (1987, 1989)

Smith and Street-Perrott, 1983
Harrison, 1993
Davis and Sellers (1987)
Davis and Sellers (1989)

CLIMATE MODELS:

mathematical representation of relationship between climatic forcing and climatic response - a test of understanding and assumptions

GOAL Explicit, repeatable results of climate forcing, based on understanding (assumptions) of meteorologic system, based on Atmospheric Physics,Gas Laws, Thermodynamics

THREE TYPES OF CLIMATE MODELS

GCM Comparisons: how well do they reproduce modern conditions?
"PIPO": Present In - Present Out
PALEOCLIMATE COLLABORATIVE RESEARCH: CLIMAP - COHMAP
Data In (Parameterization) PROVIDED BY GEOSCIENTIST
Data Out EVALUATED BY GEOSCIENTIST

CLIMAP 1976






COHMAP 1988

COHMAP "Input Paramaters"
IVA








COST

COHMAP Results
The depressed polar jetstream

see (Licciardi, 2001)


Regional Climate Readings


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