{"id":275,"date":"2017-01-23T16:36:04","date_gmt":"2017-01-23T16:36:04","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/introduction-to-oceanography\/chapter\/8-3-winds-and-climate\/"},"modified":"2021-10-26T22:11:00","modified_gmt":"2021-10-26T22:11:00","slug":"8-3-winds-and-climate","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/introduction-to-oceanography\/chapter\/8-3-winds-and-climate\/","title":{"raw":"8.3 Winds and Climate","rendered":"8.3 Winds and Climate"},"content":{"raw":"In the previous section we learned that rising air creates [pb_glossary id=\"1774\"]low pressure[\/pb_glossary] systems, and sinking air creates [pb_glossary id=\"1773\"]high pressure[\/pb_glossary]. In addition to their role in creating the surface winds, these high and low pressure systems also influence other climatic phenomena. Along the equator air is rising as it is warmed by solar radiation (section 8.2<\/a>). Warm air contains more water vapor than cold air, which is why we experience humidity during the summer and not during the winter. The water content of air roughly doubles with every 10o<\/sup> C increase in temperature. So the air rising at the equator is warm and full of water vapor; as it rises into the upper atmosphere it cools, and the cool air can no longer hold as much water vapor, so the water condenses and forms rain. Therefore,\u00a0[pb_glossary id=\"1774\"]low pressure[\/pb_glossary] systems are associated with precipitation, and we see wet habitats like tropical rainforests near the equator (Figure 8.3.1).\r\n\r\n[caption id=\"attachment_271\" align=\"aligncenter\" width=\"1024\"]\"Major<\/a> Figure 8.3.1<\/strong> Major global climatic regions in relation to atmospheric convection cells. Rising air and low pressure creates rain and wet environments at 0o<\/sup> and 60o<\/sup> latitudes, while high pressure, sinking air creates drier conditions at 30o<\/sup> and 90o<\/sup> latitudes. (Modified by PW; Map by Waitak at en.wikipedia Later version(s) were uploaded by Splette at en.wikipedia; Sun by Inductiveload (Own work Based on File:Nuvola_apps_kweather.svg); Raincloud by Calusarul (Own work); all [CC BY-SA 3.0], via Wikimedia Commons).[\/caption]After rising and producing rain near the equator, the air masses move towards 30o <\/sup>latitude and sink back towards Earth as part of the [pb_glossary id=\"1764\"]Hadley [\/pb_glossary] [pb_glossary id=\"1278\"]convection cells[\/pb_glossary]. This air has lost most of its moisture after producing the equatorial rains, so the sinking air is dry, resulting in arid climates near 30o <\/sup>latitude in both hemispheres. Many of the major desert regions on Earth are located near 30o<\/sup> latitude, including much of Australia, the Middle East, and the Sahara Desert of Africa (Figure 8.3.1). The air also becomes compressed and heats up as it sinks, absorbing any moisture from the clouds and creating clear skies. Thus [pb_glossary id=\"1773\"]high pressure[\/pb_glossary] systems are associated with dry weather and clear skies. This cycle of high and low pressure regions continues with the [pb_glossary id=\"1765\"]Ferrel [\/pb_glossary] and [pb_glossary id=\"1766\"]Polar [\/pb_glossary] convection cells, leading to rain and the boreal forests at 60o<\/sup> latitude in the Northern Hemisphere (there are no corresponding large land masses at these latitudes in the Southern Hemisphere). At the poles, descending, dry air produces little precipitation, leading to the polar desert climate.\r\n\r\nThe elevation of the land also plays a role in precipitation and climactic characteristics. As moist air moves over land and encounters mountains it rises, expands, and cools because of the declining pressure and temperature. The cool air holds less water vapor, so condensation occurs and rain falls on the windward side of the mountains. As the air passes over the mountains to the leeward side, it is now dry air, and as it sinks the pressure increases, it heats back up, any moisture revaporizes, and it creates dry, deserts regions behind the mountains (Figure 8.3.2). This phenomenon is referred to as a [pb_glossary id=\"1070\"]rain shadow[\/pb_glossary]<\/strong>, and can be found in areas such as the Tibetan Plateau and Gobi Desert behind the Himalayas, Death Valley behind the Sierra Nevada mountains, and the dry San Joaquin Valley in California.\r\n\r\n[caption id=\"attachment_272\" align=\"aligncenter\" width=\"1024\"]\"An<\/a> Figure 8.3.2<\/strong> A rain shadow. Air rising over mountains cools and condenses and forms rain, leaving dry descending air and arid conditions on the other side of the mountain (Modified by PW from Thebiologyprimer, Public domain via Wikimedia Commons).[\/caption]\r\n\r\nRising and falling air are also responsible for more localized, short-term wind patterns in coastal areas. Due to the high [pb_glossary id=\"828\"]heat capacity[\/pb_glossary] of water, land heats up and cools down about five times faster than water. During the day the sun heats up the land faster than it heats the water, setting up a [pb_glossary id=\"1278\"]convection cell[\/pb_glossary] of warmer rising air over the land and sinking cooler air over the water. This creates winds blowing from the water towards the land during the day and early evening; a [pb_glossary id=\"1108\"]sea breeze[\/pb_glossary]<\/strong> (Figure 8.3.3). The opposite occurs at night, when the land cools more quickly than the ocean. Now the ocean is warmer than the land, so air rises over the water and sinks over the land, creating a convection cell where winds blow from land towards the water. This is a [pb_glossary id=\"884\"]land breeze[\/pb_glossary]<\/strong>, which blows at night and into the early morning (Figure 8.3.3).\r\n\r\n[caption id=\"attachment_273\" align=\"aligncenter\" width=\"1024\"]\"Land<\/a> Figure 8.3.3<\/strong> Land heats and cools faster than the ocean, so during the day the land is warmer than the water leading to rising air over land and a sea breeze. At night, the ocean is warmer than the land, creating a land breeze (Modified by PW derivative work: Ingwik (Diagrama de formacion de la brisa-breeze.png) [CC-BY-SA-3.0 or GFDL (http:\/\/www.gnu.org\/copyleft\/fdl.html)], via Wikimedia Commons).[\/caption]The same phenomenon leads to seasonal climatic changes in many areas. During the winter the [pb_glossary id=\"1774\"]lower pressure[\/pb_glossary] is over the warmer ocean, and the [pb_glossary id=\"1773\"]high pressure[\/pb_glossary] is over the colder land, so winds blow from land to sea. In summer the land is warmer than the ocean, causing low pressure over the land and winds to blow from the ocean towards the land. The winds blowing from the ocean contain a lot of water vapor, and as the moist air passes over land and rises, it cools and condenses causing seasonal rains, such as the summer monsoons<\/strong> of southeast Asia (Figure 8.3.4).\r\n\r\n \r\n\r\n[caption id=\"attachment_274\" align=\"aligncenter\" width=\"530\"]\"Seasonal<\/a> Figure 8.3.4<\/strong> Seasonal wind patterns and monsoons over India. In summer, moist air from the ocean moves over the continent and rises, creating rain and the summer monsoons (pink arrows). In winter, winds are blowing from land to the sea, leading to the dry season (green arrows) (By Saravask, based on work by Planemad and Nichalp [CC BY-SA 3.0], via Wikimedia Commons).[\/caption]","rendered":"

In the previous section we learned that rising air creates low pressure systems, and sinking air creates high pressure. In addition to their role in creating the surface winds, these high and low pressure systems also influence other climatic phenomena. Along the equator air is rising as it is warmed by solar radiation (section 8.2<\/a>). Warm air contains more water vapor than cold air, which is why we experience humidity during the summer and not during the winter. The water content of air roughly doubles with every 10o<\/sup> C increase in temperature. So the air rising at the equator is warm and full of water vapor; as it rises into the upper atmosphere it cools, and the cool air can no longer hold as much water vapor, so the water condenses and forms rain. Therefore,\u00a0low pressure systems are associated with precipitation, and we see wet habitats like tropical rainforests near the equator (Figure 8.3.1).<\/p>\n

\"Major<\/a>
Figure 8.3.1<\/strong> Major global climatic regions in relation to atmospheric convection cells. Rising air and low pressure creates rain and wet environments at 0o<\/sup> and 60o<\/sup> latitudes, while high pressure, sinking air creates drier conditions at 30o<\/sup> and 90o<\/sup> latitudes. (Modified by PW; Map by Waitak at en.wikipedia Later version(s) were uploaded by Splette at en.wikipedia; Sun by Inductiveload (Own work Based on File:Nuvola_apps_kweather.svg); Raincloud by Calusarul (Own work); all [CC BY-SA 3.0], via Wikimedia Commons).<\/figcaption><\/figure>\n

The elevation of the land also plays a role in precipitation and climactic characteristics. As moist air moves over land and encounters mountains it rises, expands, and cools because of the declining pressure and temperature. The cool air holds less water vapor, so condensation occurs and rain falls on the windward side of the mountains. As the air passes over the mountains to the leeward side, it is now dry air, and as it sinks the pressure increases, it heats back up, any moisture revaporizes, and it creates dry, deserts regions behind the mountains (Figure 8.3.2). This phenomenon is referred to as a rain shadow<\/a><\/strong>, and can be found in areas such as the Tibetan Plateau and Gobi Desert behind the Himalayas, Death Valley behind the Sierra Nevada mountains, and the dry San Joaquin Valley in California.<\/p>\n

\"An<\/a>
Figure 8.3.2<\/strong> A rain shadow. Air rising over mountains cools and condenses and forms rain, leaving dry descending air and arid conditions on the other side of the mountain (Modified by PW from Thebiologyprimer, Public domain via Wikimedia Commons).<\/figcaption><\/figure>\n

Rising and falling air are also responsible for more localized, short-term wind patterns in coastal areas. Due to the high heat capacity<\/a> of water, land heats up and cools down about five times faster than water. During the day the sun heats up the land faster than it heats the water, setting up a convection cell<\/a> of warmer rising air over the land and sinking cooler air over the water. This creates winds blowing from the water towards the land during the day and early evening; a sea breeze<\/a><\/strong> (Figure 8.3.3). The opposite occurs at night, when the land cools more quickly than the ocean. Now the ocean is warmer than the land, so air rises over the water and sinks over the land, creating a convection cell where winds blow from land towards the water. This is a land breeze<\/a><\/strong>, which blows at night and into the early morning (Figure 8.3.3).<\/p>\n

\"Land<\/a>
Figure 8.3.3<\/strong> Land heats and cools faster than the ocean, so during the day the land is warmer than the water leading to rising air over land and a sea breeze. At night, the ocean is warmer than the land, creating a land breeze (Modified by PW derivative work: Ingwik (Diagrama de formacion de la brisa-breeze.png) [CC-BY-SA-3.0 or GFDL (http:\/\/www.gnu.org\/copyleft\/fdl.html)], via Wikimedia Commons).<\/figcaption><\/figure>\n

The same phenomenon leads to seasonal climatic changes in many areas. During the winter the lower pressure is over the warmer ocean, and the high pressure is over the colder land, so winds blow from land to sea. In summer the land is warmer than the ocean, causing low pressure over the land and winds to blow from the ocean towards the land. The winds blowing from the ocean contain a lot of water vapor, and as the moist air passes over land and rises, it cools and condenses causing seasonal rains, such as the summer monsoons<\/strong> of southeast Asia (Figure 8.3.4).<\/p>\n

 <\/p>\n

\"Seasonal<\/a>
Figure 8.3.4<\/strong> Seasonal wind patterns and monsoons over India. In summer, moist air from the ocean moves over the continent and rises, creating rain and the summer monsoons (pink arrows). In winter, winds are blowing from land to the sea, leading to the dry season (green arrows) (By Saravask, based on work by Planemad and Nichalp [CC BY-SA 3.0], via Wikimedia Commons).<\/figcaption><\/figure>\n
definition<\/span>

After rising and producing rain near the equator, the air masses move towards 30o <\/sup>latitude and sink back towards Earth as part of the Hadley convection cells<\/a>. This air has lost most of its moisture after producing the equatorial rains, so the sinking air is dry, resulting in arid climates near 30o <\/sup>latitude in both hemispheres. Many of the major desert regions on Earth are located near 30o<\/sup> latitude, including much of Australia, the Middle East, and the Sahara Desert of Africa (Figure 8.3.1). The air also becomes compressed and heats up as it sinks, absorbing any moisture from the clouds and creating clear skies. Thus high pressure systems are associated with dry weather and clear skies. This cycle of high and low pressure regions continues with the Ferrel and Polar convection cells, leading to rain and the boreal forests at 60o<\/sup> latitude in the Northern Hemisphere (there are no corresponding large land masses at these latitudes in the Southern Hemisphere). At the poles, descending, dry air produces little precipitation, leading to the polar desert climate.<\/p>\n