Convective Interaction with Boundary-Layer Dynamics in the Development of a Tropical Intraseasonal System

Wang, Bin; Li, Tianming

doi:10.1175/1520-0469(1994)051<1386:ciwbld>2.0.co;2

Cited by 193 publications

(183 citation statements)

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“…13g, h), thus inhibiting the formation of robust Pacific basin-wide overturning circulations. Present study reemphasizes the important role of enhanced boundary convergence ahead of MJO convection on its smooth eastward propagation (Wang and Li 1994;Hendon and Salby 1994;Jones and Weare 1996). It is expected that MJO convection in Indian Ocean will emanate a low sea level pressure tongue to its east as a Kelvin-wave response (e.g., the classic schematics of Madden and Julian 1972).…”

Section: Discussion and Concluding Remarkssupporting

confidence: 65%

Three different downstream fates of the boreal-summer MJOs on their passages over the Maritime Continent

Wang

Ren

et al. 2017

Clim Dyn

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phase. The convection of type-I and -III MJOs at eastern IO is able to generate positive boundary-layer moisture anomalies along with positive column-integrated moisture tendencies over the MC and western Pacific, thus allowing them to propagate eastward smoothly. On the other hand, the type-II MJO convection in eastern IO is associated with a very dry troposphere and negative column-integrated moisture tendency over western Pacific, which result in the rapid decay of convection over the MC. These results emphasize the important roles of robust Kelvin-wave responses and positive SST anomalies on the eastward propagation of boreal-summer MJOs over the MC through moistening the troposphere ahead of the convection.

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Section: Discussion and Concluding Remarkssupporting

confidence: 65%

Three different downstream fates of the boreal-summer MJOs on their passages over the Maritime Continent

Wang

Ren

et al. 2017

Clim Dyn

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“…The warm and cold ENSO composites for the moist stability in the model atmosphere, based on a definition analogous to that of Neelin and Held (1987), are also computed. Weaker moist stability over the central Pacific (not shown) is found during El Niñ o years, which might be conducive to the slower MJO propagation during warm events (see, e.g., Wang and Li 1994;Yu et al 1998). Another possible mechanism for the change of the MJO phase speed is the advection by the time mean flow, as the mean upper-level zonal wind is decreased during warm ENSO events in the same central Pacific region in the November-March period (not shown).…”

Section: B Observational Datamentioning

confidence: 95%

Modulation of the Madden-Julian Oscillation by ENSO: Inferences from Observations and GCM Simulations

Tam

Lau

2005

Journal of the Meteorological Society of Japan

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The impact of the El Niñ o-Southern Oscillation (ENSO) on the Madden-Julian Oscillation (MJO) is studied, based on reanalysis data and output from an ensemble general circulation model (GCM) experiment. Observed monthly sea surface temperature variations over the period of 1950-99 are imposed in the deep tropical eastern/central Pacific in the course of the SST experiment. Both GCM, and reanalysis data, indicate that intraseasonal activity of the low-level zonal wind is enhanced (reduced) over the central (western) Pacific during El Niñ o events. The propagation and growth/decay characterisitcis of the MJO in different phases of ENSO is also examined, based on a lag correlation technique. During warm events there is an eastward shift in the locations of strong growth and decay, and the propagation of the MJO becomes slower in the warm ENSO phase. These changes are reversed during La Niñ a epsiodes.Using output from the GCM experiment, the effects of ENSO on the circulation and convection during the MJO lifecycle are studied in detail. Further eastward penetration of MJO-related convection is simulated during warm events over the central Pacific. An instability index related to the vertical gradient of the moist static energy is found to be useful for depicting the onset of MJO convection along the equator. During warm events, the stronger magnitudes of this index over the central Pacific are conducive to more eastward penetration of convective anomalies in the region. These changes are mainly due to the intensified moisture accumulation at low levels. Analysis of the moisture budget suggests that the stronger moisture accumulation can be related to the increased low-level humidity over the central Pacific during warm events.

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“…Therefore the role of planetary-boundary-layer processes in organizing deep convection is emphasized (e.g. Charney, 1971;Wang and Li, 1994). One aspect of this is the reason why the ITCZ tends to form away from the Equator (Philander et al, 1996).…”

Section: Off-equatorial Convectionmentioning

confidence: 99%

A physical basis for the interannual variability of rainfall in the Sahel

Nicholson¹,

Webster²

2007

Quart J Royal Meteoro Soc

108

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A major factor in rainfall variability over Sahelian West Africa is the latitudinal location of the tropical rainbelt. When it is displaced abnormally far northward, the Sahel experiences a wet year. An anomalous southward displacement results in drought. In this paper we examine the question of what controls the location during the boreal summer, hypothesizing that inertial instability plays a role. An analysis of surface pressure and temperature fields, wind fields, divergence and vertical motion show that the criteria for inertial instability are satisfied in wet Augusts but not in dry ones. The key determinant appears to be the surface pressure gradient between the continent and the equatorial Atlantic. When this is large, inertial instability results in the development of a low-level westerly jet. The presence of this jet enhances the horizontal and vertical shear, and displaces the African Easterly Jet northwestward. Associated with this situation is strong vertical motion over the Sahel and subsidence over the Guinea Coast, producing dry conditions over the latter. The result is a rainfall dipole, one of two major modes of variability over West Africa. Important factors include sea surface temperatures (SSTs) in the equatorial Atlantic and pressure in the South Atlantic. The first of these factors suggests a link with the Atlantic Niño mode of tropical Atlantic variability; while the second suggests a possible link with the Pacific and the extratropical South Atlantic. Overall, our study relates the well-known SST influence on Sahel rainfall to atmospheric dynamics over the continent.

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Convective Interaction with Boundary-Layer Dynamics in the Development of a Tropical Intraseasonal System

Cited by 193 publications

References 0 publications

Three different downstream fates of the boreal-summer MJOs on their passages over the Maritime Continent

Three different downstream fates of the boreal-summer MJOs on their passages over the Maritime Continent

Modulation of the Madden-Julian Oscillation by ENSO: Inferences from Observations and GCM Simulations

A physical basis for the interannual variability of rainfall in the Sahel

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