Scale interaction in the Western Pacific Monsoon

Holland, Gregory

doi:10.1007/bf01022521

Cited by 210 publications

(209 citation statements)

References 57 publications

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“…Over the west Pacific, there is also a westerly jet to the south and west of the base point, which further contributes to dU/dx being negative. These results are consistent with Holland (1995)'s idea that TC genesis from easterly waves is ultimately caused by the disturbance entering a region of stretching deformation, where dU/dx ( 0, such that wave energy is enhanced on small scales via ''wave accumulation'' (Webster and Chang 1988). Similar evidence for wave accumulation playing an important role in TC genesis can be found in the recent WRF study by Done et al (2009).…”

Section: Easterly Waves and Tc Genesissupporting

confidence: 80%

Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

2009

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This study evaluates the performance of a regional climate model in simulating two types of synoptic tropical weather disturbances: convectively-coupled Kelvin and easterly waves. Interest in these two wave modes stems from their potential predictability out to several weeks in advance, as well as a strong observed linkage between easterly waves and tropical cyclogenesis. The model is a recent version of the weather research and forecast (WRF) system with 36-km horizontal grid spacing and convection parameterized using a scheme that accounts for key convective triggering and inhibition processes. The domain spans the entire tropical belt between 45°S and 45°N with periodic boundary conditions in the east-west direction, and conditions at the meridional/lower boundaries specified based on observations. The simulation covers 6 years from 2000 to 2005, which is long enough to establish a statistical depiction of the waves through space-time spectral filtering of rainfall data, together with simple lagged-linear regression. Results show that both the horizontal phase speeds and three-dimensional structures of the waves are qualitatively well captured by the model in comparison to observations. However, significant biases in wave activity are seen, with generally overactive easterly waves and underactive Kelvin waves. Evidence is presented to suggest that these biases in wave activity (which are also correlated with biases in time-mean rainfall, as well as biases in the model's tropical cyclone climatology) stem in part from convection in the model coupling too strongly to rotational circulation anomalies. Nevertheless, the model is seen to do a reasonable job at capturing the genesis of tropical cyclones from easterly waves, with evidence for both wave accumulation and critical layer processes being importantly involved.

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Section: Easterly Waves and Tc Genesissupporting

confidence: 80%

Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

2009

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“…On the other hand, as confirmed by Murakami and Matsumoto (1994), the tropical WNPM circulation exhibits a distinct tonal asymmetry in the zonal winds with westerlies (easterlies) to the west (east) of the major updraft center near 140-150E. Holland (1995) postulated that the low-level confluence zone between the monsoon westerlies and trades facilitates development and effectively traps tropical waves in a similar manner to the accumulation and emanation mechanisms described by Webster and Chang (1988). In general, the eddy wave energy fluxes are directed down the gradient of the mean tonal winds and, thus, disturbances can grow by extracting energy from the mean flow.…”

mentioning

confidence: 70%

Interaction Between the Mean Summer Monsoon Flow and 45-Day Transient Perturbations

Kawamura

Murakami

1995

Journal of the Meteorological Society of Japan

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The influence of the low-level mean summer monsoon flow on 45-day transient eddies through barotropic interaction is diagnosed by a scalar product between the horizontal shear vector and Eliassen-Palm (E-P) flux, while the dry (moist) baroclinic interaction is measured by a vector product between the vertical wind shear and the eddy sensible (latent) heat transport, which represents the vertical component of E-P fluxes. Activity of 45-day transient eddies was monitored by the evolution of kinetic energy during the 9-year period of [1985][1986][1987][1988][1989][1990][1991][1992][1993].The 45-day wave activity is relatively weak over the SEAM (Southeast Asian monsoon) domain. Absence of geographically fixed forcing makes the WNPM (western North Pacific monsoon) more violent, with the peak 45-day wave activity occurring in late August, the time of frequent development of vigorous tropical cyclones. Near the WNPM updraft center (15N, 140-150E), the E-P wave energy fluxes are oriented in a direction which causes weakening of the sheared mean zonal and meridional winds, implying barotropic amplification of 45-day waves. The weak mean temperature gradient relegates the dry baroclinic instability to that of secondary importance over the WNPM domain. This is contrasted with the significant moist baroclinic process due to an approximate perpendicular relationship between the eddy moisture transport and the strong vertical shear of the monsoon flow.Curiously, 45-day waves are quite active near Japan even during August's dry, hot climate. Neither barotropic nor dry (moist) baroclinic instability can account for late-summer disturbance activity. Evidence is presented that 45-day convective oscillations occuring over the WNPM domain induce a strong 45-day response near Japan and further eastward, possibly indicating an intraseasonal Rossby wave dispersion along the westerly jet stream. Near the Aleutian Islands, a pronounced poleward eddy sensible heat flux is directed down the mean temperature gradient, resulting in dry baroclinic amplification of mid-latitude 45-day waves via action of the Coriolis torque. An import of moisture from the WNPM source region brings about a moist baroclinic instability of extratropical 45-day waves poleward of the Pacific High.

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“…They also showed that the vapor supply from remote oceans occupies a large proportion of the total precipitable water around the cyclone center when it approached Japan; they named this type of largescale vapor transport from the tropics into the TC system the moisture conveyor belt (MCB). The TC heating acts as a source of equatorial Rossby waves and their dispersive westward phase propagation can produce a low-level cyclonic gyre and westerly flow west of the heated area (e.g., Holland 1995;Katsube and Inatsu 2016). K2014 postulated that the MCB is formed when the induced westerly flow overlaps with low-level monsoon westerlies around the South China Sea.…”

Section: Introductionmentioning

confidence: 99%

An estimation of water origins in the vicinity of a tropical cyclone’s center and associated dynamic processes

et al. 2017

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Scale interaction in the Western Pacific Monsoon

Cited by 210 publications

References 57 publications

Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

Interaction Between the Mean Summer Monsoon Flow and 45-Day Transient Perturbations

An estimation of water origins in the vicinity of a tropical cyclone’s center and associated dynamic processes

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