Query: “The Northern Hemisphere jet stream […] flow is stronger when that temperature difference is large.

Relevant passages:
Weather <=SEP=> Weather is the state of the atmosphere , to the degree that it is hot or cold , wet or dry , calm or stormy , clear or cloudy . Most weather phenomena occur in the lowest level of the atmosphere , the troposphere , just below the stratosphere . Weather refers to day-to-day temperature and precipitation activity , whereas climate is the term for the averaging of atmospheric conditions over longer periods of time . When used without qualification , `` weather '' is generally understood to mean the weather of Earth .   Weather is driven by air pressure , temperature and moisture differences between one place and another . These differences can occur due to the sun 's angle at any particular spot , which varies with latitude . The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations : the Hadley Cell , the Ferrel Cell , the Polar Cell , and the jet stream . Weather systems in the mid-latitudes , such as extratropical cyclones , are caused by instabilities of the jet stream flow . Because the Earth 's axis is tilted relative to its orbital plane , sunlight is incident at different angles at different times of the year . On Earth 's surface , temperatures usually range ± 40 ° C ( − 40 ° F to 100 ° F ) annually . Over thousands of years , changes in Earth 's orbit can affect the amount and distribution of solar energy received by the Earth , thus influencing long-term climate and global climate change .   Surface temperature differences in turn cause pressure differences . Higher altitudes are cooler than lower altitudes as most atmospheric heating is due to contact with the Earth 's surface while radiative losses to space are mostly constant . Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location . The Earth 's weather system is a chaotic system ; as a result , small changes to one part of the system can grow to have large effects on the system as a whole . Human attempts to control the weather have occurred throughout history , and there is evidence that human activities such as agriculture and industry have modified weather patterns .   Studying how the weather works on other planets has been helpful in understanding how weather works on Earth . A famous landmark in the Solar System , Jupiter 's Great Red Spot , is an anticyclonic storm known to have existed for at least 300 years . However , weather is not limited to planetary bodies . A star 's corona is constantly being lost to space , creating what is essentially a very thin atmosphere throughout the Solar System . The movement of mass ejected from the Sun is known as the solar wind .

Jet stream <=SEP=> Jet streams are fast flowing , narrow , meandering air currents found in the atmosphere of some planets , including Earth . On Earth , the main jet streams are located near the altitude of the tropopause and are westerly winds ( flowing west to east ) . Their paths typically have a meandering shape . Jet streams may start , stop , split into two or more parts , combine into one stream , or flow in various directions including opposite to the direction of the remainder of the jet . The strongest jet streams are the polar jets , at 9 - above sea level , and the higher altitude and somewhat weaker subtropical jets at 10 - . The Northern Hemisphere and the Southern Hemisphere each have a polar jet and a subtropical jet . The northern hemisphere polar jet flows over the middle to northern latitudes of North America , Europe , and Asia and their intervening oceans , while the southern hemisphere polar jet mostly circles Antarctica all year round .   Jet streams are the product of two factors : the atmospheric heating by solar radiation that produces the large scale Polar , Ferrel , and Hadley circulation cells , and the action of the Coriolis force acting on those moving masses . The Coriolis force is caused by the planet 's rotation on its axis . On other planets , internal heat rather than solar heating drives their jet streams . The Polar jet stream forms near the interface of the Polar and Ferrel circulation cells ; while the subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells .   Other jet streams also exist . During the Northern Hemisphere summer , easterly jets can form in tropical regions , typically where dry air encounters more humid air at high altitudes . Low-level jets also are typical of various regions such as the central United States .   Meteorologists use the location of some of the jet streams as an aid in weather forecasting . The main commercial relevance of the jet streams is in air travel , as flight time can be dramatically affected by either flying with the flow or against , which results in significant fuel and time cost savings for airlines . Often , the airlines work to fly ` with ' the jet stream for this reason . Dynamic North Atlantic Tracks are one example of how airlines and air traffic control work together to accommodate the jet steam and winds aloft that results in the maximum benefit for airlines and other users . Clear-air turbulence , a potential hazard to aircraft passenger safety , is often found in a jet stream 's vicinity , but it does not create a substantial alteration on flight times .

Pacific Ocean <=SEP=> The Pacific Ocean is the largest and deepest of the Earth 's oceanic divisions . It extends from the Arctic Ocean in the north to the Southern Ocean ( or , depending on definition , to Antarctica ) in the south and is bounded by Asia and Australia in the west and the Americas in the east .   At 63,800,000 sqmi in area , this largest division of the World Ocean -- and , in turn , the hydrosphere -- covers about 46 % of the Earth 's water surface and about one-third of its total surface area , making it larger than all of the Earth 's land area combined .   The equator subdivides it into the North Pacific Ocean and South Pacific Ocean , with two exceptions : the Galápagos and Gilbert Islands , while straddling the equator , are deemed wholly within the South Pacific . The Mariana Trench in the western North Pacific is the deepest point in the world , reaching a depth of 35797 ft.   Both the center of the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean .   Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times , the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great `` southern sea '' which he named Mar del Sur ( in Spanish ) . The ocean 's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521 , as he encountered favorable winds on reaching the ocean . He called it Mar Pacífico , which in both Portuguese and Spanish means `` peaceful sea '' .