Comprehensive Study Guide on El Nifffo, La Nifffa, and the ENSO Cycle

Definitions and Core Phenomena of the Equatorial Pacific

• El Niño Definition: This phenomenon is defined as "unusually warm sea surface temperatures along the Equatorial Pacific Ocean."

• La Niña definition: This phenomenon represents "unusually cool sea surface temperatures along the Equatorial Pacific Ocean."

• Geographic Scope: Both phenomena occur exclusively along the Equatorial Pacific. They represent a change from the "norm" of sea surface temperatures specifically in that region and nowhere else.

• The El Nifffo Southern Oscillation (ENSO):

  • ENSO refers to the "process of sea surface temperature change along the Equatorial Pacific Ocean."

  • The term "oscillation" describes the cyclical nature of these temperatures, which move "back and forth" over a period of many years.

  • The cycle transitions from a "normal state" (the standard temperature of the ocean) into an El Nifffo state or a La Nifffa state, before eventually returning to normal.

Geographic Regions of the Equatorial Pacific

• Regional Mapping: Scientists have divided the Equatorial Pacific into specific zones to track temperature fluctuations. These regions are bounded by Australia and Indonesia to the West and South America to the East.

• Nifffo 1 and 2:

  • Location: Directly off the coast of South America (near Peru).

  • Historical Significance: This was the first area where temperature changes were officially discovered.

• Nifffo 3: A region located further out into the Equatorial Pacific from the South American coast.

• Nifffo 4: This region is located even further West along the Equatorial Pacific, nearing Australia and Indonesia.

• Nifffo 3.4:

  • Location: A specific "hashed" region on scientific maps that is split between the Nifffo $4$ and Nifffo $3$ regions.

  • Function: This is currently the primary area used by scientists to predict the occurrence of El Nifffo. It serves as a "telltale area" because temperatures often warm here before they warm in the Nifffo $1$ and $2$ regions.

Historical Discovery and the Role of Peruvian Fishermen

• Initial Observations: The discovery of the sea surface temperature change was not initially made by scientists, but by fishermen working off the coast of Peru.

• Impact on Industry: Fishermen noticed that their business would suffer as fish died off in large numbers, often during the months of December, January, and February.

• Cyclic Nature: These events did not happen every year; the fishermen observed them occurring approximately every $7$ years.

• Scientific Expansion: Eventually, scientists realized that these coastal changes were part of a larger phenomenon encompassing the entire Equatorial Pacific. Research indicated that these changes could influence global atmospheric and ocean circulation patterns.

The Oceanic Nifffo Index (ONI) and Defining "Normal"

• Dataset: The ONI uses historical data spanning from January $1950$ to January $2016$.

• Defining Normal (The Zero Baseline):

  • The baseline (represented as $0$ on the index) represents the mean baseline normal temperature.

  • To calculate this "normal," scientists take the temperature readings from the Nifffo $3.4$ region over the past $30$ years and calculate the average.

• Measuring Anomalies: To determine if an El Nifffo or La Nifffa is occurring, scientists measure the difference between the current temperature and this $30$-year average.

• The Three-Month Average: A single daily reading is insufficient to declare an El Nifffo. To filter out "weird data points," scientists use a three-month average of the sea surface temperatures in the Nifffo $3.4$ region.

Classification and Intensity Thresholds

• Declaration Thresholds:

  • El Nifffo: Declared when the three-month average is more than $0.5\,^{\circ}\text{C}$ warmer than the normal baseline.

  • La Nifffa: Declared when the three-month average is more than $0.5\,^{\circ}\text{C}$ cooler than the normal baseline.

  • Neutral/Normal: Readings within $0.5\,^{\circ}\text{C}$ in either direction of the baseline are considered normal.

• El Nifffo Intensity Categories:

  • Weak: Change of $0.5\,^{\circ}\text{C}$ to $1\,^{\circ}\text{C}$.

  • Moderate: Change of $1\,^{\circ}\text{C}$ to $1.5\,^{\circ}\text{C}$.

  • Strong: Change of $1.5\,^{\circ}\text{C}$ to $2\,^{\circ}\text{C}$.

  • Very Strong: Change of $2\,^{\circ}\text{C}$ or more.

• La Nifffa Intensity Categories: Ranked similarly as Weak, Moderate, and Strong. As of the lecture recording, a "very strong" La Nifffa had not yet been recorded.

Historical Records of Very Strong El Nifffo Events

• There are only three "very strong" El Nifffo events in recorded history (within the context of this study):

  • $1982$ to $1983$.

  • The event spanning July $1998$.

  • The $2015$ to $2016$ El Nifffo.