Climate Variability Andy Hoell - andrew_hoell@uml.edu Earth and - - PowerPoint PPT Presentation

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Climate Variability Andy Hoell - andrew_hoell@uml.edu Earth and - - PowerPoint PPT Presentation

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Climate Variability Andy Hoell - andrew_hoell@uml.edu Earth and Environmental Systems II 13 April 2011 The Earth System Earth is made of several components that individually change throughout time, interact with each of the other

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Climate Variability

Andy Hoell - andrew_hoell@uml.edu Earth and Environmental Systems II 13 April 2011

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The Earth System

  • Earth is made of several

components that individually change throughout time, interact with each of the other components and modify the other components while being modified by the

  • ther components
  • Unus pro omnibus, omnes

pro uno

Source: http://www.icess.ucsb.edu/

13 April 2011 Climate Variability 2

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Definition of Climate

  • Climate is the instantaneous measurements of

environmental variables averaged over longer periods of time

  • Though we typically think of weather and climate

from an atmospheric point of view, where weather are the instantaneous measurements and climate are the averaged variables, we can apply this definition to all aspects of the Earth System

13 April 2011 Climate Variability 3

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Climate Variability Definition

  • Weather varies over long periods of time, and so too

does climate

  • Climate Variability (alt. Climate Change) is the

variation of environmental variables on time scales

  • f greater than a couple of weeks
  • Atmosphere: e.g. Temperature, Humidity
  • Ocean: e.g. Sea Surface Temperatures, Sea Height
  • In society, (i.e. at home, bus stop, etc) the term

“Climate Change” will result in a discussion on human-induced climate variability – unless you want a political argument, don’t use this definition

  • If you want to talk about such things as El Nino, use

the term Climate Variability

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Modes of Climate Variability

  • Components of the Earth System change on

different time scales, can be observed in different variables and are usually oscillatory

  • Each discernable change in a variable on

climate time scales is called a climate mode

  • Modes of climate variability observed in one

component of the Earth System influence each

  • f the other components of the Earth System
  • Modes of climate variability compliment,

augment and compete with other modes of climate variability

13 April 2011 Climate Variability 5

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Climate Mode Time Scale Example

1 day 1 mo 1 yr 10 yr 100 yr 103 yr 104 yr 105 yr

Weather Seasonal Cycle ENSO PDO Orbital Parameters Humans Monsoons

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Separating Climate Variability

  • Climate variability can be triggered by an individual

component of the climate system or multiple components working synergistically

  • So-called “natural climate variability” originates within the Earth

System

  • So-called “human-induced” climate variability results from the

actions of humans

  • The effects of the changes in a particular sector of the

Earth System manifest throughout the entire system, making it extremely difficult to determine the root cause and effect of the initial change

  • In short, separating individual modes of climate

variability, determining their influence on the Earth System and understanding how each mode interacts with other modes is extremely difficult, if not impossible

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Identifying Climate Modes

  • Observation
  • Some climate modes occur regularly (i.e. seasonal cycle) or are

so strong they can’t be missed (i.e. ENSO).

  • Statistical Analysis
  • Some climate modes occur irregularly with varying magnitudes

(i.e. Madden-Julian Oscillation) or on time scales too long or short for us to notice easily (Pacific Decadal Oscillation)

  • Climate Modes we haven’t figured out yet
  • Occur on time scales that we have insufficient data or tools to

measure

  • A note on time scales – some climate modes are elusive
  • r we just don’t understand their behavior, as they
  • perate on time scales that we have insufficient data for

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Measuring Climate Modes

  • Climate modes are measured through statistical

analysis of varying complexity

  • Some modes are simply averages of a particular

variable over a given domain, as is the case with

  • ceanic Nino indices
  • Other modes are measured through more

complicated analyses of patterns throughout time, involving one or more variables, as is the case with the Pacific Decadal Oscillation, for example

13 April 2011 Climate Variability 9

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Seasonal Cycle

  • The regular oscillation in weather patterns that
  • ccurs each year as a result of Earth’s orbital

parameters is called the seasonal cycle

  • On “human time scales”, i.e. 1 day to a couple

hundred years, this mode provides the largest variation of weather and climate

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U.S. Precip. Seasonal Cycle

JFM AMJ JAS OND

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Seasonal Precipitation

1 2 3 4 5 6 7 8 9 10 11 12 2 4 6 8 10 12 14 16 18 20 Annual Precipitaiton Climatology Precipitation (cm) Month Boston Seattle

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El Nino-Southern Oscillation

  • Climate mode that is “quasi-periodic” and occurs an average of

every five years

  • Two phases: El Nino and La Nina
  • El Nino observed as warm waters (relative to average conditions)

across the equatorial Pacific Ocean

  • La Nina observed as cool waters(relative to average conditions)

across the equatorial Pacific Ocean

  • Growth and decay of ENSO events linked to both ocean and

atmospheric circulation – no definite mechanism is understood

  • The tropical atmospheric component associated with El Nino/La

Nina is called the Southern Oscillation

  • ENSO is most commonly observed using area-averages of sea

surface temperatures over the Pacific

  • The SO is most commonly observed using pressure differences

between Tahiti (west Pacific) and Darwin (Australia)

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Nino Indices

2 1.5 1 0.5 0.5 1 1.5 2

  • 2
  • 19982002 Monthly SST Index Anomaly (

N4

The Nino indices are one way of measuring El Nino/La Nina, and are simply averaged sea surface temperature anomalies over the colored regions Nino4 index for 1998-2002. Major tick marks are January of each year. Notice the La Nina from mid-1998 to early 2001 and the El Nino thereafter.

Source: http://www.bom.gov.au/climate/enso/indices/about.shtml

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Average Conditions Schematic

Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html

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El Nino Schematic

Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html

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La Nina Schematic

Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html

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Global Climate Impacts of ENSO

  • The tropical circulation is modified in the

presence of ENSO extremes

  • The extratropical (mid-latitude) circulation is also

modified

  • The atmospheric energy budget is modified in the

presence of ENSO extremes, which influences the circulation of the atmosphere

  • Circulation modifications that result in changes

to weather and climate vary by location – over the U.S., most impacts occur along the West Coast and southern half of the country

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