Due to Earth'saxial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night. There is also a seasonal variation in temperatures, which lags the variation in day and night. Conventionally,winter in the Northern Hemisphere is taken as the period from theDecember solstice (typically December 21UTC) to theMarch equinox (typicallyMarch 20 UTC), whilesummer is taken as the period from theJune solstice through to theSeptember equinox (typically on 23 September UTC). The dates vary each year due to the difference between thecalendar year and theastronomical year. Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events includeEl Niño–Southern Oscillation.
Trade winds blow from east to west just above the equator. The winds pull surface water with them, creating currents, which flow westward due to theCoriolis effect. The currents then bend to the right, heading north. At about 30 degrees north latitude, a different set of winds, thewesterlies, push the currents back to the east, producing a closed clockwise loop.[2]
Its surface is 60.7% water, compared with 80.9% water in the case of theSouthern Hemisphere, and it contains 67.3% of Earth's land.[3] The continents ofNorth America and mainlandEurasia are located entirely in the Northern Hemisphere, together with about two-thirds ofAfrica and a small part ofSouth America.
During the 2.5 million years of thePleistocene, numerous cold phases calledglacials (Quaternary ice age), or significant advances of continental ice sheets, inEurope andNorth America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorterinterglacials which lasted about 10,000–15,000 years. The last cold episode of thelast glacial period ended about 10,000 years ago.[4] Earth is currently in an interglacial period ofthe Quaternary, called theHolocene.[5] The glaciations that occurred during the glacial period covered many areas of the Northern Hemisphere.
Northern hemisphere glaciation during the lastice ages. The setup of 3 to 4 kilometer thick ice sheets caused asea level lowering of about 120 m.
TheArctic is a region around theNorth Pole (90°latitude). Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in the form of snow. Areas inside theArctic Circle (66°34′ latitude) experience some days in summer when the Sun never sets, and some days during the winter when it never rises. The duration of these phases varies from one day for locations right on the Arctic Circle to several months near the Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and theTropic of Cancer (23°26′ latitude) lies theNorthern temperate zone. The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather.
Tropical regions (between the Tropic of Cancer and the Equator, 0° latitude) are generally hot all year round and tend to experience arainy season during the summer months, and adry season during the winter months.
In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of theCoriolis effect. As a result, large-scale horizontal flows of air or water tend to form clockwise-turninggyres.[6] These are best seen in ocean circulation patterns in theNorth Atlantic andNorth Pacific oceans.[6] Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast.[7] For the same reason, flows of air down toward the northern surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic ofhigh pressure weather cells in the Northern Hemisphere. Conversely, air rising from the northern surface of the Earth (creating a region of low pressure) tends to draw air toward it in a counterclockwise pattern.Hurricanes andtropical storms (massive low-pressure systems) spin counterclockwise in the Northern Hemisphere.[8]
The shadow of a sundial moves clockwise on latitudes north of thesubsolar point and anticlockwise to the south. During the day at these latitudes, the Sun tends to rise to its maximum at a southerly position. Between the Tropic of Cancer and the Equator, theSun can be seen to the north, directly overhead, or to the south at noon, depending on the time of year. In the Southern Hemisphere, the midday Sun is predominantly in the north.
When viewed from the Northern Hemisphere, theMoon appears inverted compared to a view from the Southern Hemisphere.[9][10] The North Pole faces away from theGalactic Center of theMilky Way. This results in the Milky Way being sparser and dimmer in the Northern Hemisphere compared to the Southern Hemisphere, making the Northern Hemisphere more suitable for deep-space observation, as it is not "blinded" by the Milky Way.[citation needed]
As of 2015, the Northern Hemisphere is home to approximately 6.4 billion people, which is around 87.0% of the Earth's total human population of 7.3 billion people.[11][12][13]
List of continents, countries or territories, and oceans in the Northern Hemisphere
^abThe continent itself is entirely within the Northern Hemisphere. However, some overseas territories of the countries ofFrance,Norway and theUnited Kingdom are in the Southern Hemisphere.
^Calculated from World Population Yearbook 2019(in thousands)World total population: 7,359,970Northern Hemisphere population: 6,405,03087.0%Southern Hemisphere population: 954,94013.0%Note 1) If there is no data for 2019, the latest data was used.Note 2) Countries with land that straddles the equator are divided into half populations in each of the Northern and Southern Hemispheres.
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