L. 5: Climactic Variability v. Trends, C. 4-Trenberth

Question 1

Time Scales Decomposition

Answer 1

Trend or 'climate change' signal
Interannual variability(e.g., ENSO)
Decadal Variability (e.g., PDO, IPO, AMO, AO, NAO)
Sub-seasonal (e.g., MJO)

Question 2

Objectives of decomposition

Answer 2

Determine relative contribution of each to climatic variability.
Sources of climatic information.
To inform adaptation or risk mitigation strategies. (Need to know which type of climate variability to deal with for agriculture, food security. Different planning in area, different solution, depending on influence of trend or decadal.

Question 3

Trend or ‘climate change’ signal

Answer 3

Represents the responses to the external forcings of the climate system: solar activity, GHGs, volcanic activity, etc. Does not include ocean temp.
Globally averaged temperature from a large ensemble of computer models is used to isolate the forced changes.

Question 4

Decadal variability

Answer 4

All fluctuations that are at least a decade long. It can present changes in its amplitude or frequency along the 20th century (not necessarily a periodic oscillation).
After removing the ‘trend,’ decadal component from the residuals is isolated using a ‘low-pass’ filter.

Question 5

Interannual variability

Answer 5

Year-to-year variability. More than 1 year but less than 10. Not perfectly periodic (e.g., El Nino/La Nina 2 to 7 years).
Isolated using high-pass filters that retain high frequency.

Question 6

Variability of precipitation

Answer 6

Varies a lot by region and over time. As more local, less data and less reliable.

Question 7

Subseasonal variability

Answer 7

Variability within a year.

Question 8

ENSO

Answer 8

En Nino-Southern Oscillation
Interannual. El Nino is a warming of at least 0.5 deg C (0.9F) averaged over the east-central (tropical) Pacific that happens at irregular intervals of 2-7 years, and lasts 9 months to 2 years. Increased SST. Associated with negative SOI values (below normal pressure over Tahiti and above normal pressure of Darwin, Australia). Hot air rises in Central Pacific, travels east, then west before cooling and descending. Less cold water and cool air on South America. Less nutrients, fish.
La Nina is the cold phase when cold pool in eastern Pacific intensifies and trade winds strengthen and move west, pushing warmer air and water farther west than usual.

Question 9

Decadal

Answer 9

PDO (Pacific Decadal Oscillation) – detected as warm or cool surface waters in the Pacific north of 20 deg N.
IPO (Interdecadal Pacific Oscillation) – similar to PDO but longer (15-30 yrs), and affects north and south Pacific.

Question 10

Sub-seasonal variation

Answer 10

MJO (Madden Julian Oscillation), 41-53 day zonal eastward-propagating circulation anomaly, impacts precipitation worldwide.

Question 11

Intraseasonal variability

Answer 11

Daily, active and break phases, even during monsoon seasons.

Question 12

Clausius-Clapeyron relationship

Answer 12

As temperature goes up, capacity of atmosphere to hold water goes up. More up means more comes down.

Question 13

Advection

Answer 13

The transfer of heat or matter by the flow of a fluid, esp. horizontally in the atmosphere or the sea.

Question 14

Convection

Answer 14

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. The process by which masses of relatively warm air are raised into the atmosphere, often cooling and forming clouds, with compensatory downward movements of cooler air.

Question 15

Precipitation simulations

Answer 15

Trenberth – all climate models contain errors in these simulations because they fail to account for the amount, location, patterns, seasonal variation, and characteristics of precipitation (frequency, duration and intensity).