What Will El Niño Bring to Iran and the World This Year?

El Niño is a periodic phenomenon, recurring roughly every two to seven years, during which surface waters of the tropical eastern Pacific Ocean become unusually warm. Its appearance can produce major weather anomalies around the world, including floods, drought, famine, and the spread of disease.

The article explains the Spanish name El Niño as a reference to the Christ child, reflecting the historical association of the phenomenon with the Christmas season.

Image from the original article

Pacific sea-surface temperature anomalies during the period discussed in the original 2015 article.

According to information then being reported by the U.S. National Oceanic and Atmospheric Administration (NOAA) and NASA, the 2015 El Niño was strengthening. Several observed variables resembled those of the powerful 1997 event. Measurements of Pacific sea-surface height and temperature, together with wind patterns, showed cooling in parts of the western Pacific while tropical waters farther east were warming substantially. [source]

Record-Breaking Cold in the United States and Iran

While Monday's snowy weather over the Zagros region and Iran's Central Plateau has intensified the winter cold for residents of many Iranian cities, people in the United States have also been dealing with exceptional cold over the past few days.

Temperatures have dropped sharply across the northern and central United States. Cities along the Gulf of Mexico coast, whose climate is reminiscent of coastal cities in southern Iran, experienced temperatures below freezing last night, while farther north temperatures fell as low as −20°C. Cold approaching −25°C in Chicago led to the cancellation of all flights. Forecasts also indicated that freezing conditions would persist across the central and eastern United States for another two to three days.

The article attributes these conditions to a weakening of the fast atmospheric currents circulating around the polar regions. Under normal conditions, these currents prevent frozen polar air from penetrating farther south. Similar conditions have also contributed to falling temperatures elsewhere.

Accordingly, temperatures in Iran were expected to decline noticeably over the following few days, with the largest drops in the northwest, along the Zagros slopes, and across the central desert regions, where temperatures could fall to −10°C. These conditions were expected to continue into the following week.

With another system entering Iran from the west and southwest the following Saturday, renewed snowfall was considered likely in western Iran, the Zagros region, and central areas. The author notes that further analysis of the system would be posted by Saturday.

Why Is It Still Rainy in Iran and Snowy in Canada?

As I mentioned in one of my previous posts, in climate discussions we deal with a parameter called the Arctic Oscillation (AO), which plays an important role in determining weather conditions at middle and more northerly latitudes. As explained in that post, the Arctic Oscillation has two phases, negative and positive, and fluctuates between them from year to year. In some years the weather of the Northern Hemisphere is influenced by the negative phase of the AO, and in others by the positive phase.

During the positive phase, weather at northern latitudes near the polar regions is colder than normal, while farther south, where more people live, conditions are warmer than normal (Figure 1).

Image from the original article

Figure 1. Left: effects of the positive phase on Northern Hemisphere weather. Right: effects of the negative phase on these regions.

For example, 1390 SH was strongly influenced by the positive phase. In Canada, this contributed to weather warmer than normal and a very short, pleasant winter, while severe cold remained confined to the polar regions. This pattern reversed in 1391 SH: during the year just ended, the middle latitudes of the Northern Hemisphere experienced very cold weather under the influence of the negative phase.

That pattern is still continuing. During the past week, for example, temperatures in Canada were 10–15°C colder than during the corresponding period the previous year, and here we celebrated Nowruz amid exceptional snow and blizzards.

Although the negative phase brings cold, snow, and blizzards to regions such as Canada and northern Europe, at middle latitudes such as the Middle East and Iran it is accompanied by abundant precipitation. Because much of Iran has an arid or semi-arid climate, this is a welcome oscillation phase for those regions.

Nevertheless, forecasts indicate that the pressure system over the polar regions will weaken during the next few weeks (Figure 2), so we should soon see warmer weather in more northerly areas. This means relatively greater precipitation for regions such as northern Europe and North America and, unfortunately, warmer and drier weather—relative to the preceding few weeks—for Mediterranean regions and the Middle East.

AO

Figure 2. Forecast AO index.