Correlation, MJO, Monsoons - Notes

Correlation Coefficient

  • Represents the relationship between two variables (e.g., temperature and precipitation).

  • Statistically represents how well two variables vary with each other in time or space (i.e., covariance).

  • The correlation coefficient ranges between -1 and 1. Values closer to 1 (or -1) indicate a stronger covarying relationship between the two variables.

  • Positive correlations indicate a direct relationship between two variables. Negative values indicate an inverse relationship.

Pearson Correlation Coefficient

  • The Pearson correlation coefficient is the covariance between two variables (x and y).

  • Illustrates the strength of linear relationships.

Correlation Coefficient - Important Notes

  • The correlation coefficient is a simple way to examine the linear relationship between two variables.

  • Correlation does not imply causation!

  • Correlation can be a powerful statistical tool in hydroclimatology, as it can increase our understanding of how hydroclimate variables are related.

Madden-Julian Oscillation (MJO)

  • Discovered in 1971 by Dr. Roland Madden and Dr. Paul Julian of the American National Center for Atmospheric Research (NCAR).

  • The MJO is a 30-60 day oscillation in tropical rainfall with a parent circulation.

  • The MJO is most active over the Indian and Pacific Oceans.

  • It impacts the monsoon, tropical cyclone development, and overall precipitation.

  • Does not always exist; appears 40-50% of the time.

MJO Characteristics:

  • Eastward movement is observed.

  • Involves both upper-level (200 mb) and lower-level (850 mb) winds.

  • Features include upward motion over southern Asia, downward motion over associated with stormy and wet conditions and downward motion over Middle Pacific related to sunny and dry conditions.

MJO Propagation

  • The MJO interacts with the Monsoon and can enhance precipitation in some locations while suppressing monsoon precipitation in others.

MJO Phases

  • Phase 1: Enhanced convection (rainfall) develops over the western Indian Ocean.

  • Phases 2 and 3: Enhanced convection moves eastward over eastern Africa, the Indian Ocean, and parts of the Indian subcontinent.

  • Phases 4 and 5: Enhanced convection reaches the Maritime Continent (Indonesia and West Pacific).

  • Phases 6, 7, and 8: Enhanced rainfall moves further eastward over the western Pacific, eventually dying out in the central Pacific. The next MJO cycle begins.

Monsoons

  • Differential heating between the land and ocean yields a pressure gradient and drives a circulation (Halley 1686).

  • Monsoon winds are deflected by the Earth’s rotation (Hadley 1735).

  • Seasonal oscillation of solar heating with net heating drives the migration of the equatorial trough and the intertropical convergence zones.

Hadley Circulation

  • Non-Rotating Earth: Features ascent in the tropics and descent at the poles.

  • Rotating Earth: Includes mid-latitude and polar cells. Westerlies, Northeasterly Trades and Southeasterly Trades are important features. Descent at ~30°N and ~30°S. Ascent at the tropics

Trade Winds - Edmond Halley (1686)

  • Diagram showing trade winds across the globe.

Terrestrial/Ocean Interactions

  • Air heats more quickly over land than water, becoming more buoyant over the land, producing ascent and a relative minimum in pressure (low pressure).

  • The opposite occurs over the water (sinking air and high pressure).

  • A Land/Ocean circulation develops.

Semi-Permanent Pressure Systems

  • Illustrates observed surface wind-flow patterns in January (austral summer) and July (austral winter).

Austral/Asian Monsoon Conditions

  • Boreal Summer (left) and Boreal Winter (right) conditions are shown.

Rainfall Patterns

  • January and July average rainfall (mm/dd) from 1998 to 2007 are compared.

Classic Monsoon Region

  • Geographic location is indicated. Covers central Africa, Indian Subcontinent, most of China, Japan, and Maritime continent

Tropical Rainfall

  • Tropical rainfall as a function of seasonality (December - February and June - August).

Geographical Extent of the Global Surface Monsoons

  • Red, green, and blue areas indicate the tropical, subtropical, and temperate-frigid monsoons, respectively.

  • Red and blue thick lines represent the ITCZ in summer and winter, respectively.

    • ITCZ significantly higher in summer, especially over Africa, South Asia and Maritime continent

Monsoon Systems

  • OLR, 200hPa Streamlines, 850 hPa Wind Climatology (1979-1995) Examples for American, African, and Asian-Australian monsoons.

The Role of the Monsoon in India and Australia

  • Illustrates the position of the Intertropical Convergence Zone (ITCZ) in December-January (lower position) and June-July (higher position).

Monsoon Impacts - India and Australia

  • As the ITCZ swings north during the summer months, it brings monsoon rains to Kozhikode, India.

  • As the ITCZ drops south during summer in the Southern Hemisphere, it brings monsoon rains to Darwin, Australia.

Indian Monsoon

  • Winter (dry) and Summer (wet) monsoon conditions.

  • Nagpur, India is used as an example.

  • Precipitation patterns at Nagpur, India, are also given.

The African Monsoon

  • African Monsoon Peak: OLR, 200 hPa Streamlines, 850 hPa Wind Climatology (1979-1995).

  • Illustrates the Intertropical Discontinuity/Front (ITD/ITF).

African Rainfall Patterns

  • High rainfall central Africa June-Sep. High rainfall southeastern Africa Jan-March.

  • Harmattan conditions (very hot and dry) are indicated.

The North American Monsoon

  • Upper-level jet stream and subtropical high influence the monsoon.

The North American Monsoon - Annual Precipitation

  • JJAS Average Precipitation (mm) and JJAS Annual Contribution (Percent) from 1948-2010.

Monsoon Example - Arizona

  • Average monthly precipitation for Phoenix and Tucson, Arizona.