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CHAPTER 8 CLIMATIC CLASSIFICATION

By Jose Hill,2014-07-09 07:27
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CHAPTER 8 CLIMATIC CLASSIFICATION

CHAPTER 8 CLIMATIC CLASSIFICATION

Early Attempts at Global Climatic Classification

    ; Very early attempts by the ancient Greeks at classifying climate were logic-based, and resulted in

    Paramenides’ identification of three principal climate regions; the Frigid Zone, the Temperate Zone,

    and the Torrid Zone

    ; Other climatic classification schemes followed, including one by Hipparchus who updated the

    Paramenides classification by including information on the calculated day length for particular

    locations

    ; Logic-based climatic classification systems ruled until the development and proliferation of weather

    recording instrumentation

The Classical Age of Climatic Classifications

    ; Modified Köppen Climatic Classification System

    o Utilizes monthly temperature and precipitation data in making calculations upon which the

    classification scheme is based

    o Köppen identified five main climatic groups: A (tropical), B (arid), C (mesothermal or

    mid-latitude mild), D (microthermal or mid-latitude cold), and E (polar)

    o In general, the A, C, and D climates support the growth of trees, whereas the B and E

    climates do not, being either too dry or too cold, respectively

    o In the case of A, C, and D climates, the second-order subdivision refers to the precipitation

    seasonality (with “f” representing climates that are wet year-round, “s” indicating summer

    dry climates, “w” representing winter dry climates, and “m” representing tropical monsoon

    conditions)

    o For B climates, the second-order subdivision is “S” if the dry climates are only semi-arid,

    and “W” if the dry climates are true deserts

    o In the case of “E” climates, the second-order subdivision is “T” for the milder Tundra

    sub-type of polar climate, while “F” (frozen) is used to represent the Ice Cap subtype

    o For the mesothermal and microthermal climates, third-order subdivisions identify the

    characteristics of summer temperatures, with “a” representing hot summers, “b” used for

    warm summers, “c” indicating mild summers, and the rare “d” indicating cool summers

    o Arid climates have a third-order subdivision of “h” and “k” which are used to denote “hot”

    and “cold” arid or semi-arid regions, respectively

    ; Thornthwaite Climatic Classification System

    o Is built on the physical interactions between local moisture and temperature rather than

    only the precipitation and temperature data. It represents a more sophisticated and precise

    scheme of classification based on local surface water balances

    o Thornthwaite devised a number of specific indices to quantify necessary climatic

    components, including the moisture index (MI) and the potential evapotranspiration

    (PE) rate for a location

    o Thornthwaite also derived a Thermal Efficiency Index (T/ET) of the ratio of temperature

    (T) to a calculated evapotranspiration (ET) value, and a Dryness Index (DI) and

    Humidity Index (HI) to identify the times of the year with water deficit or surplus ; Other Global Classification Systems

    o The Holdridge Life Zones Climatic Classification System was intended to be for global

    application, but it became most widely used in tropical areas, where it has proved useful in

    ecological and alpine applications

    o The Budyko Climatic Classification System uses an energy budget approach to

    classifying climates

    ? 2012 Jones and Bartlett Learning, LLC

Genetic Classifications

    ; Strategy is to classify climates solely on the basis of the major forcing mechanisms that make climate

    the way that it is

    ; The Bergeron Climatic Classification System, devised by Swedish meteorologist Tor Bergeron in

    1928, is one early-modern genetic classification system. This system categorizes the climate at a

    location based on the manual and somewhat subjective determination of frequency with which it is

    dominated by certain types of weather

    ; Air Masses and Fronts

    o The Bjerknes model classified areas of a surface cyclone and associated pressure features

    into specific sectors with each section exhibiting particular weather characteristics

    o An air mass is a body of air that is relatively uniform in its characteristics for distances of

    hundreds to thousands of kilometers, with its characteristics resulting largely from the

    characteristics of the place where the air mass forms the source region

    o Air mass types include: the intensely-cold and dry Arctic (A) type; the slightly warmer

    and more humid continental polar (cP); cool, humid maritime polar (mP); warm, humid

    maritime tropical (mT), hot, dry continental tropical (cT), and the “E” air masses of

    equatorial origin a more extreme version of the mT type

    o A cold front represents a situation in which a colder air mass is pushing a warmer air mass

    back toward its source region

    o A warm front is a region where a warmer air mass is displacing a colder one poleward

    o In a stationary front, the cold and warm air mass may temporarily be at a stalemate, with

    neither air mass pushing the other backward

    o A cold front and warm front generally emanate from a central region of low pressure in a

    midlatitude wave cyclone

    o After the midlatitude wave cyclone travels eastward for a few days in the mid-latitude

    westerlies, the cold front will actually catch up with the warm front near the cyclonic

    center, where the two fronts are closest to each other, resulting in an occluded front

Local and Regional Classifications

    ; The Lamb Weather Types and Muller Weather Types

    o Aare based on the mid-latitude wave cyclone model

    o These are manual systems meaning that the researcher subjectively categorizes the types

    based on his/her interpretation of the weather map on a given day

Quantitative Analysis to Derive Climatic Types

    ; Eigenvector Analysis

    o Iis helpful for identifying relationships between two different sets of variables (such as

    spatial data points, observations of an atmospheric variable through time, or atmospheric

    variables) to be analyzed simultaneously

    o In synoptic typing, eigenvector analysis may be used whereby the atmospheric variables

    may collectively represent the properties that dominate, and locations where similar

    characteristics of the atmosphere tend to occur simultaneously would be categorized as part

    of the same type for that entity of time

    ; Cluster Analysis

    o The actual classification process in any eigenvector analysis (including PCA) comes when

    the matrix of loadings or scores (which usually represents the spatial and temporal

    variability (respectively) in the data set) is subjected to a cluster analysis ? 2012 Jones and Bartlett Learning, LLC

    o Several types of cluster analysis can be used with each giving a slightly different

    classification result, but all have the common goal of selecting the groups so that the

    distance in n-dimensional space between the points within the cluster (within-group

    variability) is minimized

    ; Hybrid Techniques

    o Typically require the investigator to identify “prototype” atmospheric circulation patterns

    manually a “textbook” case of each particular genetic category, with the computerized

    cluster analysis used to categorize all other days (or months, if monthly mean data are used)

    automatically, quickly, and efficiently, into the group with the prototype day (or month)

    that the weather map for the day (or month) in question most resembles

    ? 2012 Jones and Bartlett Learning, LLC

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