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1. Introduction The Hadley circulation and the intertropical convergence zone (ITCZ) are important components of the general circulation of the earth’s atmosphere. A historically important and influential theory of the Hadley circulation is proposed by Held and Hou (1980 , hereafter HH ). HH offered a theory of the axisymmetric circulation that is driven thermally by Newtonian relaxation toward a radiative equilibrium temperature, which has a cos 2 ϕ dependence on latitude ϕ . The HH
1. Introduction The Hadley circulation and the intertropical convergence zone (ITCZ) are important components of the general circulation of the earth’s atmosphere. A historically important and influential theory of the Hadley circulation is proposed by Held and Hou (1980 , hereafter HH ). HH offered a theory of the axisymmetric circulation that is driven thermally by Newtonian relaxation toward a radiative equilibrium temperature, which has a cos 2 ϕ dependence on latitude ϕ . The HH
1. Introduction The general circulation of the atmosphere plays a key role in determining the surface climate of Earth. In low latitudes, the Hadley circulation determines the structure of convergence zones, which in turn shape the precipitation distribution. Therefore, changes in the atmospheric circulation must have contributed to climate changes in Earth’s history. The changes associated with Earth’s orbital parameters are of particular interest because they cause variations in top
1. Introduction The general circulation of the atmosphere plays a key role in determining the surface climate of Earth. In low latitudes, the Hadley circulation determines the structure of convergence zones, which in turn shape the precipitation distribution. Therefore, changes in the atmospheric circulation must have contributed to climate changes in Earth’s history. The changes associated with Earth’s orbital parameters are of particular interest because they cause variations in top
1. Introduction The Hadley circulation (HC) features ascending motion in the tropics and descending motion in the subtropics (e.g., Glickman 2000 ), and it plays vital roles in balancing the atmospheric water vapor, mass, and energy budgets globally. Variations in the HC can affect tropical precipitation, tropical cyclone activity, and even the climate in the middle to high latitudes (e.g., Lindzen 1994 ; Chang 1995 ; Hou 1998 ; Held 2001 ; Trenberth and Stepaniak 2003 ; Doos and Nilsson
1. Introduction The Hadley circulation (HC) features ascending motion in the tropics and descending motion in the subtropics (e.g., Glickman 2000 ), and it plays vital roles in balancing the atmospheric water vapor, mass, and energy budgets globally. Variations in the HC can affect tropical precipitation, tropical cyclone activity, and even the climate in the middle to high latitudes (e.g., Lindzen 1994 ; Chang 1995 ; Hou 1998 ; Held 2001 ; Trenberth and Stepaniak 2003 ; Doos and Nilsson
. For example, the common interpretation of monsoons as land–sea breeze circulations emphasizes the surface temperature gradient, which can affect the surface winds by modifying pressure or geopotential gradients that enter the horizontal momentum equation (e.g., Lindzen and Nigam 1987 ). In contrast, angular momentum-conserving Hadley circulation theories estimate the strength of the Hadley circulation, in an energetic sense, from the top-of-atmosphere energy balance ( Held and Hou 1980 ). We
. For example, the common interpretation of monsoons as land–sea breeze circulations emphasizes the surface temperature gradient, which can affect the surface winds by modifying pressure or geopotential gradients that enter the horizontal momentum equation (e.g., Lindzen and Nigam 1987 ). In contrast, angular momentum-conserving Hadley circulation theories estimate the strength of the Hadley circulation, in an energetic sense, from the top-of-atmosphere energy balance ( Held and Hou 1980 ). We
1. Introduction The tropical Hadley circulation (HC) is defined as the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30°S and 30°N. It is one of the most important and largest atmospheric circulations. The HC is mainly a thermally driven circulation, with warmer air rising in the tropics because of the release of latent heat and colder air sinking in the subtropics in both hemispheres, generating a closed circulation in each hemisphere ( Held and Hou 1980 ). This
1. Introduction The tropical Hadley circulation (HC) is defined as the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30°S and 30°N. It is one of the most important and largest atmospheric circulations. The HC is mainly a thermally driven circulation, with warmer air rising in the tropics because of the release of latent heat and colder air sinking in the subtropics in both hemispheres, generating a closed circulation in each hemisphere ( Held and Hou 1980 ). This
1. Introduction Monsoons are generally viewed as regionally concentrated, thermally direct overturning circulations in the latitude–height plane, with ascending motion in the summer hemisphere subtropics and descending motion in the winter hemisphere ( Newell et al. 1972 ; Gadgil 2003 ; Bordoni and Schneider 2008 ). These monsoonal circulations dominate the solstitial zonally averaged Hadley circulation, which is characterized by a strong and broad cross-equatorial winter cell and a very weak
1. Introduction Monsoons are generally viewed as regionally concentrated, thermally direct overturning circulations in the latitude–height plane, with ascending motion in the summer hemisphere subtropics and descending motion in the winter hemisphere ( Newell et al. 1972 ; Gadgil 2003 ; Bordoni and Schneider 2008 ). These monsoonal circulations dominate the solstitial zonally averaged Hadley circulation, which is characterized by a strong and broad cross-equatorial winter cell and a very weak
). Coincident with these poleward migrations in seasonal-mean TC latitudes, there has been an expansion of the dominant feature of the large-scale tropical atmospheric flow, the Hadley circulation (HC; e.g., Lucas et al. 2014 ). Reported magnitudes for the migration of the HC poleward extent are approximately 0.5°–0.81° lat decade −1 (e.g., Hu and Fu 2007 ; Stachnik and Schumacher 2011 ; Davis and Rosenlof 2012 ; Allen et al. 2012 ; Nguyen et al. 2013 ; Davis and Birner 2013 ). There is thus some
). Coincident with these poleward migrations in seasonal-mean TC latitudes, there has been an expansion of the dominant feature of the large-scale tropical atmospheric flow, the Hadley circulation (HC; e.g., Lucas et al. 2014 ). Reported magnitudes for the migration of the HC poleward extent are approximately 0.5°–0.81° lat decade −1 (e.g., Hu and Fu 2007 ; Stachnik and Schumacher 2011 ; Davis and Rosenlof 2012 ; Allen et al. 2012 ; Nguyen et al. 2013 ; Davis and Birner 2013 ). There is thus some
1. Introduction The Hadley circulation (HC) is a central element of Earth’s climate, transporting heat and momentum poleward and affecting the extent of the wet tropical and dry subtropical regions, and the properties of the midlatitude baroclinically unstable region. Understanding how the extent of the wet and dry regions, the HC strength (HCS), and the properties of the subtropical jets respond to variations of external parameters is therefore critical for understanding Earth’s climate
1. Introduction The Hadley circulation (HC) is a central element of Earth’s climate, transporting heat and momentum poleward and affecting the extent of the wet tropical and dry subtropical regions, and the properties of the midlatitude baroclinically unstable region. Understanding how the extent of the wet and dry regions, the HC strength (HCS), and the properties of the subtropical jets respond to variations of external parameters is therefore critical for understanding Earth’s climate
1. Introduction The Hadley circulation is a thermally driven circulation that features ascent of equatorial air to a height of about 15 km, transportation aloft toward the poles, descent at the subtropics, and a return flow near the surface. These features offer an explanation for the persistence and extent of the trade winds and the subtropical high pressure belt that dominate the climate of the tropics and subtropics. The descending branch of the Hadley cell (HC) is associated with subsidence
1. Introduction The Hadley circulation is a thermally driven circulation that features ascent of equatorial air to a height of about 15 km, transportation aloft toward the poles, descent at the subtropics, and a return flow near the surface. These features offer an explanation for the persistence and extent of the trade winds and the subtropical high pressure belt that dominate the climate of the tropics and subtropics. The descending branch of the Hadley cell (HC) is associated with subsidence
1. Introduction Steady-state, axisymmetric solutions for the circulation in a differentially heated fluid on a rotating sphere have been advanced over the past few decades as a means of understanding the Hadley circulation (e.g., Schneider 1977 ; Held and Hou 1980 ). The associated theory emphasizes conservation of absolute angular momentum in the free troposphere, which results in a nonlinear dependence of circulation strength and extent on the imposed thermal forcing. Results of this theory
1. Introduction Steady-state, axisymmetric solutions for the circulation in a differentially heated fluid on a rotating sphere have been advanced over the past few decades as a means of understanding the Hadley circulation (e.g., Schneider 1977 ; Held and Hou 1980 ). The associated theory emphasizes conservation of absolute angular momentum in the free troposphere, which results in a nonlinear dependence of circulation strength and extent on the imposed thermal forcing. Results of this theory
