On the Role of Transient Eddies in the Tropical Troposphere

Nitta, Tsuyoshi

doi:10.2151/jmsj1965.48.4_348

Cited by 28 publications

(12 citation statements)

References 28 publications

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“…8a with the mean zonal wind as contours). Similar negative correlation between temperature and v wind near the central Pacific has been noticed in a number of studies concerning summertime synoptic-scale activity (e.g., Nitta 1970). 6a), there is a strong positive vorticity anomaly at the upper level located at 160°W.…”

Section: B Vertical Structure Of Circulation and Wave Activitysupporting

confidence: 85%

“…The low-level "cold core" along the trough axis has been pointed out by many studies (see, e.g., Chang et al 1970). Interestingly, Nitta (1970) and Reed and Recker (1971) found equatorward heat flux at ϳ700 hPa associated with the synoptic-scale eddies over the western to central Pacific. This is consistent with the large conversion from eddy available potential energy to kinetic energy, the former of which is mainly generated from diabatic heating (Lau and Lau 1992).…”

Section: A Structure and Wave Characteristicsmentioning

confidence: 72%

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The Origin and Dispersion Characteristics of the Observed Tropical Summertime Synoptic-Scale Waves over the Western Pacific*

Tam

2006

Monthly Weather Review

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The origin, initiation, and dispersion behavior of the observed summertime synoptic-scale disturbances in the tropical western Pacific are studied. These westward-propagating disturbances have the strongest growth rate over the region of ϳ130°-160°E off the equator. The three-dimensional wave activity flux associated with a wave packet in the vicinity of this region is computed. In general, wave activity is directed westward. There is accumulation of activity flux, which gives rise to the amplification of waves. In the low levels, such accumulation can be attributed to the convergence of both the mean flow and the intrinsic group velocity. Diabatic forcing also contributes to the growth of disturbances and is most important in the 500-600-hPa layer. Along the east-west-oriented "storm tracks" of the synoptic-scale disturbances, there are two different dynamical regimes. West of ϳ150°E, enhanced convection is associated with increased specific humidity at the top of the planetary boundary layer and is in phase with positive low-level vorticity anomalies. To the east of 150°E the vorticity leads the convection by about one-quarter of a wavelength. This phase relationship can be explained by adiabatic dynamics and is related to the positive vertical shear of the mean zonal flow in the latter region.Near and to the east of the date line where disturbances are initiated in the low levels, the heat flux associated with the synoptic-scale eddies is negative (i.e., ЈT Ј Ͻ 0) from about 300 to 700 hPa. This implies downward-directed wave activity. In the upper troposphere at the same geographical location, there is southward wave activity from the extratropics penetrating into the Tropics. These findings suggest that summertime synoptic-scale disturbances may originate from extratropical forcing. This hypothesis is supported by a case study. Intrusion of high potential vorticity into the Tropics was seen to be followed by downward development, resulting in low-level disturbances that subsequently moved westward in the western Pacific and grew.

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Section: B Vertical Structure Of Circulation and Wave Activitysupporting

confidence: 85%

Section: A Structure and Wave Characteristicsmentioning

confidence: 72%

The Origin and Dispersion Characteristics of the Observed Tropical Summertime Synoptic-Scale Waves over the Western Pacific*

Tam

2006

Monthly Weather Review

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“…In contrast, during July 1975, negative conversion occurred in the upper half of the troposphere. As Kung pointed out, his results were also in close agreement with profiles obtained by Nitta [8] and Wallace [ 19] who integrated the cospectra of vertical motion and temperature time series over a limited region in the Marshall islands area. The conversion of energy in the whole column from 1000 to 100 mb showed a negative value, indicating the predominance of conversion of kinetic to available potential energy in a tropical atmosphere with weak convection and with no significant disturbances.…”

Section: ~[V]supporting

confidence: 86%

The kinetic energy budget over the West Pacific during dominant trade wind and active monsoon regimes

Reiter

1983

Arch. Met. Geoph. Biocl. A.

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From upper-air network data and NMC tropical wind analyses over the West Pacific during July 1972 and July 1975, the kinetic energy balance in large-scale disturbances and in the general flow of the tropical circulation was calculated. During July 1972, when an active monsoon and its attendant intertropical convergence zone (ITCZ) dominated much of the tropical West Pacific and five typhoons and a depression formed in the area under study, cross-isobaric generation of the eddy kinetic energy took place in the upper (300 to 100 rob) and lower troposphere (1000 to 700 mb), with weak dissipation at middle levels. The total amount of eddy kinetic energy produced in the area during July 1972 was five times greater than during July 1975, when strong southeast trade winds prevailed over most of the West Pacific and no typhoons formed in that area. In the 1972 case, a significant portion of the generated eddy kinetic energy was exported out of the region, whereas in the 1975 case the area imported a considerable amount of eddy kinetic energy to compensate for dissipation mainly in the upper troposphere. For the month with an active monsoon regime the eddy conversion from available potential to kinetic energy, -[w*c~*], was large, with a maximum in the layer 500 to 200 mb, due to the strong convective warming, whereas for the month with a prevailing trade-wind regime only weak positive eddy conversion (increase of eddy kinetic energy) took place in the lower troposphere, with a considerable portion of the troposphere being dominated by negative eddy conversion. The kinetic energy balance in the general flow of the two contrasting periods revealed opposite behavior. The budget for July 1972 was characterized by cross-isobaric destruction of kinetic energy in the whole troposphere, with a maximum at waddle levels, and with a negative dissipation term which compensated for the cross-isobaric destruction through the interaction between the grid-scale flow and subgrid scale disturbances. In contrast, the cross-isobaric generation and positive dissipation term constituted a balance of

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“…The 10-20-day oscillation in the tropics was reported by several previous studies (e.g., Wallace and Chang 1969;Nitta 1970;Chang et al 1970;Yanai and Murakami 1970;Murakami 1971). It was referred to as the quasibiweekly oscillation (QBWO) by Murakami (1976) and Krishnamurti and Bhalme (1976), who pointed out the remarkable QBWOs that exist in the entire monsoon region.…”

Section: Introductionmentioning

confidence: 76%

Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

Wen

Zhang

et al. 2010

Journal of the Atmospheric Sciences

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The structure and evolution features of the quasi-biweekly (10-20 day) oscillation (QBWO) in boreal spring over the tropical Indian Ocean (IO) are investigated using 27-yr daily outgoing longwave radiation (OLR) and the National Centers for Environment Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data. It is found that a convective disturbance is initiated over the western IO and moves slowly eastward. After passing the central IO, it abruptly jumps into the eastern IO. Meanwhile, the preexisting suppressed convective anomaly in the eastern IO moves poleward in the form of double-cell Rossby gyres. The analysis of vertical circulation shows that a few days prior to the onset of local convection in the eastern equatorial IO an ascending motion appears in the boundary layer.Based on the diagnosis of the zonal momentum equation, a possible boundary layer-triggering mechanism over the eastern equatorial IO is proposed. The cause of the boundary layer convergence and vertical motion is attributed to the free-atmospheric divergence in association with the development of the barotropic wind. It is the downward transport of the background mean easterly momentum by perturbation vertical motion during the suppressed convective phase of the QBWO that leads to the generation of a barotropic easterly-the latter of which further causes the free-atmospheric divergence and, thus, the boundary layer convergence. The result suggests that the local process, rather than the eastward propagation of the disturbance from the western IO, is essential for the phase transition of the QBWO convection over the eastern equatorial IO.

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On the Role of Transient Eddies in the Tropical Troposphere

Cited by 28 publications

References 28 publications

The Origin and Dispersion Characteristics of the Observed Tropical Summertime Synoptic-Scale Waves over the Western Pacific*

The Origin and Dispersion Characteristics of the Observed Tropical Summertime Synoptic-Scale Waves over the Western Pacific*

The kinetic energy budget over the West Pacific during dominant trade wind and active monsoon regimes

Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

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