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

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 components and modify the other components while being modified by the other components • Unus pro omnibus, omnes pro uno Source: http://www.icess.ucsb.edu/ 13 April 2011 Climate Variability 2

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

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 of 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 13 April 2011 Climate Variability 4

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 of 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

Climate Mode Time Scale Example Humans PDO Orbital Parameters ENSO Monsoons Seasonal Cycle Weather 1 day 1 mo 1 yr 10 yr 100 yr 10 3 yr 10 4 yr 10 5 yr 13 April 2011 Climate Variability 6

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 13 April 2011 Climate Variability 7

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 or we just don’t understand their behavior, as they operate on time scales that we have insufficient data for 13 April 2011 Climate Variability 8

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 oceanic 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

Seasonal Cycle • The regular oscillation in weather patterns that occurs 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 13 April 2011 Climate Variability 10

U.S. Precip. Seasonal Cycle JFM AMJ JAS OND 13 April 2011 Climate Variability 11

Seasonal Precipitation Annual Precipitaiton Climatology 20 Boston Seattle 18 16 14 Precipitation (cm) 12 10 8 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 Month 13 April 2011 Climate Variability 12

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) 13 April 2011 Climate Variability 13

Nino Indices The Nino indices are one way of measuring El Nino/La Nina, and are simply averaged sea surface temperature anomalies over the colored regions Source: http://www.bom.gov.au/climate/enso/indices/about.shtml 1998 � 2002 Monthly SST Index Anomaly ( 2 Nino4 index for 1998-2002. Major 1.5 tick marks are January of each year. 1 0.5 Notice the La Nina from mid-1998 to 0 early 2001 and the El Nino � 0.5 � 1 thereafter. � 1.5 N4 � 2 2 13 April 2011 Climate Variability 14 � � � � � � � � � � � �

Average Conditions Schematic Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html 13 April 2011 Climate Variability 15

El Nino Schematic Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html 13 April 2011 Climate Variability 16

La Nina Schematic Source: http://www.pmel.noaa.gov/ tao/elnino/nino_normal.html 13 April 2011 Climate Variability 17

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 13 April 2011 Climate Variability 18