Happy perihelion! At 4.17pm GMT today the Earth is closer to the sun than at any time in the year, a distance of 147,105,000km. That is about five million kilometres closer than the Earth’s furthest point, aphelion, which happens on July 4 this year. At perihelion the sun appears very slightly larger and sunlight is about 7 per cent stronger than at aphelion, but the difference is so small it’s hardly noticeable. Far more important in the northern hemisphere’s winter climate is the Earth’s axis tilted away from the sun, leaving us with less solar energy and shorter hours of daylight.
The timing of perihelion shifts over a period of about 22,000 years, a cycle that influences global climate, such as ice ages. A team of scientists have also found that perihelion affects a yearly weather pattern — a cold tongue of seas that appears across equatorial parts of the Pacific. This effect has been known to appear at this time of year thanks to the Earth’s tilt, but the study revealed that perihelion also drives this phenomenon.
The Pacific’s cold tongue influences El Niño and La Niña in the Pacific, which tend to peak in the northern hemisphere’s winter. And so the effect of perihelion can have a huge impact on weather patterns across large parts of the globe.
“Our study found that the timing of perihelion . . . has an important influence on climate in the tropical Pacific,” Anthony Broccoli of Rutgers University said.
The changing distance between the Earth and sun operates in much the same way as the familiar seasonal monsoon winds between north and south parts of the Tropics, except the wind changes around perihelion are coming from an east-west monsoon. So when Earth is closest to the sun, these winds are strong but when the sun is at its furthest distance the winds become weak. These changes in the wind are then relayed to the Eastern Pacific and help to drive the annual cycle of the Pacific’s cold tongue.
