Major weather patterns and past climates Flashcards
Hurricanes more typically affect where?
The eastern seaboard of N America
Along the west coast of N America, cold currents and upwelling keep the Pacific ocean cold, and high pressure generates stable air, so late summer tropical storms are rare…..
What weather changes can occur during an El Nino?
Eastern Pacific hurricanes occur?
Drought and wildfires in eastern and central Australia
Drought and fire in Indonesia
What is La Nina?
A turbo charged normal situation.
Normally the warm water pulls up in the western pacific, much more upwelling and colder conditions in the eastern pacific.
What is ENSO?
El Nino southern oscillation
We can use statistics to describe the El Nino using?
An index summarising status – based on a set of key conditions.
Around a standardised mean- departures from mean = anomalies.
The six components of the multivariate ENSO index are…
Sea-level pressure (often compared Darwin vs Tahiti)
Zonal and meridional components of the surface wind
Sea-surface temperature (especially east Pacific)
Surface air temperature
Total cloudiness fraction of the sky.
Values applied according to a formula to derive a single figure that describes when ENSO has occurred.
Other effects of El Niño and La Niña (the extreme years)
Atlantic hurricane season stronger in La Niña years, weaker in El Niño years
SW USA precipitation higher in El Niño years – can lead to flooding
N coast of S America – El Niño brings rains, floods, and the suppressed upwelling in the E Pacific reduces the fisheries
Estimates of global economic losses from 1998 El Niño are ca $80 billion
Climate oscillations =
Internal variability of the climate system
Short-term (decadal-scale) oscillations are inherent in climate system (“internal” variability). It is now recognized that some oscillations can span several decades, however.
Indices of climate oscillations. These are usually contrasting spatial poles of temperature, pressure, precipitation, etc, that exist in two extreme states and also intermediate states. They are useful descriptions of climate oscillations. Several can be combined.
When does the PDO (Pacific Decadal Oscillation- a robust, recurring pattern of ocean-atmosphere climate) have a negative value?
When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific.
When does the PDO (Pacific Decadal Oscillation- a robust, recurring pattern of ocean-atmosphere climate) have a positive value?
When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific
Basic pattern of the monsoon circulation is…
reversed summer and winter winds related to pressure centres over Asia.
Increased sophistication of understanding of the monsoon:
- Not just about “Sea breeze” – winter high and summer low in Asia, jet streams control flows
- The movement of the ITCZ/heat equator explains the trade winds drawn to the continent in summer, convergence rising air, deflected by Coriolis
- Role of jet streams in switching monsoon on and off and funnelling air across the ocean from high-pressure areas
Simple basis of monsoon summer vs winter
Movement of the ITCZ
Summer = convergence and rising air over the S Asian continent
Onshore flow brining moist air from the oceans and generating rain.
Winter high sits over cold Asian continent
Offshore flow of dry cool air.
Jet switching as a monsoon trigger (a sudden change that causes a rapid onset of the summer monsoon flow)
Winter westerly jet splits around Tibet. Southern branch over S central Asia associated with descending air and high pressure.
In summer, southern branch disappears, air rises above ITCZ trough, causing upper-level high.
This generates a high-level easterly jet, associated with rising air.
What are teleconnections?
Patterns in different areas are correlated and may have cause-effect relationship
