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Sarah M. Kang, Dargan M. W. Frierson, and Isaac M. Held

1. Introduction One of the most prominent features of the tropical climate is the intertropical convergence zone (ITCZ). Small changes in the structure and position of the ITCZ can produce large changes in local precipitation. Recent studies suggest that tropical precipitation can be influenced by extratropical forcing. For example, modeling studies show that the Atlantic ITCZ is displaced southward by freshwater input in the northern North Atlantic ( Stouffer et al. 2006 ; Zhang and Delworth

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Yoshio Kawatani, Shingo Watanabe, Kaoru Sato, Timothy J. Dunkerton, Saburo Miyahara, and Masaaki Takahashi

the mean upward motion existing in the equatorial lower stratosphere, which has an estimated magnitude of approximately 0.3 mm s −1 (e.g., Mote et al. 1996 , 1998 ; Schoeberl et al. 2008 ). On the other hand, the downward-propagating speed of the QBO is approximately 0.5 mm s −1 . The equatorial mean upward motion makes the QBO phase move upward, whereas the wave forcing makes the QBO phase move downward. Therefore, the wave forcing should have a stronger effect than the equatorial upward flow

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S. Ramachandran

Satheesh and Srinivasan (2006 , henceforth SS06 ) discussed a method to determine aerosol radiative forcing from spectral optical depths. A more refined methodology applicable to a wide variety of environments, which employs stringent criteria and is statistically rigorous, for the first time has been published earlier by Ramachandran and Jayaraman (2003) , the details of which are given below. In addition the shortcomings in the method given in SS06 are pointed out in this work. The

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Rafail V. Abramov and Andrew J. Majda

1. Introduction The low-frequency response to changes in external forcing for various components of the climate system is a central problem of contemporary climate change science. In particular, in the atmosphere the response of the low-frequency teleconnection patterns such as the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the Pacific–North America pattern (PNA), which steer the storm tracks, is a fundamental issue. Leith (1975) suggested that if the climate system

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Orli Lachmy and Nili Harnik

and McIntyre 1985 ) that suggest that in the nonlinear limit a CL can undergo cycles of absorption, reflection, and overreflection, settling at the end on a fully reflective state. However, these studies focus on the CL dynamics alone. To understand how the CL will affect the wave–mean flow equilibration, an understanding of the CL dynamics needs to be combined with other factors of the dynamics of the full system and their interplay. The equilibrated state also depends on the radiative forcing

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William J. Randel, Fei Wu, and Piers Forster

. For SH winter a weak wave 1 is also evident, with maximum near the date line (somewhat downstream of the strongest winds, but distant from the eddy storm track maximum in the southern Indian ocean; Trenberth 1991 ). Overall the GPS data suggest that the strength of the TIL does not vary strongly in longitude, nor is it closely linked to storm track statistics. 4. A radiative forcing mechanism for the TIL The global GPS observations demonstrate that the TIL is a ubiquitous feature of the

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Jeremiah P. Sjoberg and Thomas Birner

simple models—the Holton–Mass model—has been utilized in many studies because of its relative simplicity. This one-dimensional, β -plane channel model explores the interaction of waves specified by eddy potential vorticity and the zonal-mean zonal wind. It has been shown to capture zonal wind and eddy heat flux vacillations characteristic of SSWs from forcing by steady bottom boundary wave amplitudes ( Holton and Mass 1976 ) and from forcing by sinusoidal bottom boundary wave amplitudes of varying

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Hyun-Joo Choi, Hye-Yeong Chun, and In-Sun Song

. 1998 ) in the middle atmosphere. Convectively forced gravity waves are known to play crucial roles in providing the momentum forcing required to drive the quasi-biennial oscillation (QBO) and the mesospheric semiannual oscillation (SAO) in the Tropics ( Alexander and Holton 1997 ; Piani et al. 2000 ). As interest increases in understanding convective gravity waves, there have been many numerical modeling studies of convective gravity waves and their generation mechanisms (e.g., Pandya and

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Bingqi Yi, Ping Yang, Bryan A. Baum, Tristan L'Ecuyer, Lazaros Oreopoulos, Eli J. Mlawer, Andrew J. Heymsfield, and Kuo-Nan Liou

individual cases, thereby limiting the representativeness of the results. These earlier studies helped, however, establish the need to update the effects of ice crystal roughness on optical property parameterizations and to revisit the radiative forcing estimates. Both issues are pursued comprehensively in this paper. We describe the data and methodology used in this study in section 2 . Section 3 shows the simulated ice roughness effects by single-column radiative transfer models (RTMs) and an AGCM

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Brian J. Hoskins and Gui-Ying Yang

1. Introduction The possible forcing of the tropical atmosphere from higher latitudes was proposed by Charney (1963) . However, Charney (1969) showed that only Rossby waves with westward phase speed greater than that of the zonally averaged westward (easterly) zonal flow could propagate. Since these waves have little energy, it was assumed the relevant problem for high-latitude forcing of the Tropics became that of absorption of stationary and eastward-moving Rossby waves at critical lines

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