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The solar wind streams away from the Sun in all directions at speeds of several hundred km/s in the Earth's vicinity. At some distance from the Sun, well beyond the orbit of Neptune , this supersonic wind slows down as it encounters the gases in the interstellar medium .
The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of 300–500 km/s, a temperature of ~ 100 kilokelvin and a composition that is a close match to the ...
Researchers were unsure exactly where the Alfvén critical surface of the Sun lay. Based on remote images of the corona, estimates had put it somewhere between 10 and 20 solar radii from the surface of the Sun. [5] On April 28, 2021, during its eighth flyby of the Sun, NASA's Parker Solar Probe (PSP) encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated ...
Observations of CME speeds indicate that CMEs tend to accelerate or decelerate until they reach the speed of the solar wind (§ Interactions in the heliosphere). When observed in interplanetary space at distances greater than about 50 solar radii (0.23 AU) away from the Sun, CMEs are sometimes referred to as interplanetary CMEs , or ICMEs .
One astronomical unit (about 150 million kilometres; 93 million miles) is defined as the mean distance between the centers of the Sun and the Earth. The instantaneous distance varies by about ± 2.5 million kilometres (1.6 million miles) as Earth moves from perihelion around 3 January to aphelion around 4 July. [36]
A short burst of high speed wind is termed a wind gust; one technical definition of a wind gust is: the maxima that exceed the lowest wind speed measured during a ten-minute time interval by 10 knots (19 km/h; 12 mph) for periods of seconds. A squall is an increase of the wind speed above a certain threshold, which lasts for a minute or more.
At 7:15 a.m. EDT on Saturday, July 8, around 99% of the Earth's population will see sunlight in the sky - as long as it isn't cloudy. This equates to approximately 7.9 billion people across North ...
[4] [11] Because of the relatively smooth water surface, wind speeds do not decrease as much close to the sea as they do on land. [12] Over a city or rough terrain, the wind gradient effect could cause a reduction of 40% to 50% of the geostrophic wind speed aloft; while over open water or ice, the reduction may be only 20% to 30%. [13] [14]