Short-Term Climate Variability and Atmospheric Teleconnections from Satellite-Observed Outgoing Longwave Radiation. Part I: Simultaneous Relationships

Impact of the sea surface temperature anomalies (SSTAs) on atmospheric circulations are studied with emphasis on the winter climate in Japan with the use of an atmospheric general circulation model.The empirical orthogonal function analyses are performed for precipitation, geopotential height at 500mb and surface air temperature. It is shown that leading eigenvectors of precipitation are zonally elongated in the tropics and that the distribution of positive and negative precipitation anomalies is dependent on the SST and precipitation field in the control run. Surface air temperature in East Asia is mostly governed by the temperature contrast between Japan-East China region and the Sea of Okhotsk. This is associated with high pressure anomalies in the North Pacific Ocean, which weakens the cold surge from Siberia. This circulation is found in the first eigenvector in the present experiment El(Z500) and is dominant in the run which uses the composited January SSTA observed during warm winter in Japan. The simulated anomalies in mid-latitude circulation correspond well with the observations.An additional run with the SSTA over the equator east of the dateline gives the largest anticyclonic circulation response over the North Pacific Ocean and the warmest surface air temperature anomalies in East Asia. The pattern relevant to warm winter in Japan is not a simple atmospheric response to tropical heating. It is conceivable that inherently there is a dominant circulation mode like El(Z500) and that this mode can be activated either by a direct and/or an indirect orographic effect or by anomalous heating induced by the SSTA.This pattern can be understood as a response to subtropical mass source/sink distribution under the framework of a linear theory.

Section: Interpretation Of Mid-latitude Responsementioning

confidence: 67%

“…A steady-state atmospheric response to an equatorial forcing is studied by Matsuno (1966), Gill (1980), Lau and Lim (1982), Lim and Chang (1983) and Heckley and Gill (1984). It is shown that for an isolated heat source over the equator, the Kelvin and the gravest Rossby modes dominate in the tropics.…”

Section: Interpretation Of Mid-latitude Responsementioning

confidence: 99%

A Numerical Experiment on Sea Surface Temperature Anomalies and Warm Winter in Japan

Kitoh

1988

“…In these regions the convective activity is also strong (low OLR) even in the mean state. During the 82-83 ENSO event, the warm SST region expanded eastward and the region of the strong 30-60 day signal of OLR also expanded eastward (Lau and Chan, 1985). Sardeshmukh and Hoskins (1985) also demonstrated that during the 82-83 event the 200mb vorticity activity of the 30-60 day time scale is very strong over the central Pacific around the east of the date line.…”

Section: Introductionmentioning

confidence: 89%

“…For instance, the appearance of anomalous convection in the central Pacific and drought over the maritime continent -Australia region during the ENSO (E1-Nino Southern Oscillation) events is recognized as a shift in the distribution of the 30-60 day oscillation (see, Fig. 15 of Lau and Chan, 1985).…”

Section: Introductionmentioning

confidence: 99%

The 30-40 Day Oscillations Simulated in an "Aqua Planet" Model

Hayashi

Sumi

1986

207

Numerical experiments using a general circulation model (GCM) were performed for the purpose of investigating the possibility of the generation of a long period (30-40 days) oscillation as a collective motion of cumulus activity (so-called wave-CISK) along the equator of an ocean covered globe ("aqua planet"). In our model, the SST distribution was symmetric about the equator and uniform in the longitudinal direction.The results of a 90 day integration exhibited the spontaneous appearance of a collective motion of convective activity together with an east-west wavenumber one circulation (the "30 day oscillation"). The characteristics of this east-west circulation resemble those of the observed 30-60 day oscillation in the actual atmosphere. The 30 day oscillation is characterized by a superposition of two different scales: the scale of precipitation patterns ("super clusters") which is nearly equal to the equatorial radius of deformation, and the scale observed as the modulation of precipitation patterns and the east-west circulation with a wavenumber one. The whole structure moves eastward at a slow phase speed (15m/s).The results also exhibited the spontaneous formation of double ITCZs around the equator. Thus the production of the double ITCZ structure does not necessarily require a minimum SST at the equator. In the equatorial region between the north and south ITCZs, active convection forms super clusters, while in the regions poleward of the ITCZs, active convection forms tropical cyclones.Another experiment without the moist processes resulted in the abrupt disintegration of the 30 day oscillation into Kelvin and Rossby waves. This indicates that strong mode coupling between the equatorial free waves is required in order to maintain the 30 day oscillation. The slow phase speed, the strong mode coupling and the double structure in scale indicate that the collective motion of convective activity along the equator cannot be explained simply as a Kelvin wave mode of the linear equatorial wave-CISK theory presented so far. The 30 day oscillation should be regarded as a new type solution of the equatorial wave-CISK problem.

“…11-18, following Livezey and Chen (1983), Lau and Chan (1983), and T. Murakami (1987). A common confidence level of 95 % is used for testing local and global significance.…”

Section: Relationship With Tropical Cyclogenesismentioning

confidence: 99%

An Intraseasonal Amplitude Modulation of the Short-term Tropical Disturbances over the Western Pacific

Yamazaki¹,

Murakami²

1989

The intraseasonal change of the activities of the short-term tropical disturbances are investigated in terms of their amplitude modulation. It has been revealed that the amplitude modulation in the tropics bears a periodicity around 30 days. It was also found that the enhanced phase of the amplitude modulation is often accompanied by the clustered genesis and/or development of tropical cyclones. The space-time analysis of the amplitude modulation has shown that it consists of two characteristic modes. One is the eastward-propagating mode with tonal wavenumber 1. Another mode shows a westward propagation and zonal wavenumber 4 to 6 as a characteristic longitudinal scale. Both modes appear equally significant in leading to enhanced disturbance activity.The large-scale circulation changes associated with the intraseasonal amplitude modulation are also investigated referring to the modulation over the tropical western Pacific. The composite analysis has revealed that the lower tropospheric westerly and the upper-level easterly are enhanced at the time of the enhanced activity of the tropical disturbances. The horizontal distribution of the circulation anomalies indicates that an intrusion of the low-level westerlies into the western Pacific takes place at this stage from the equatorial Indian Ocean through the South China Sea. This intrusion is also accompanied by enhanced cross-equatorial southerlies over the Indonesian region. In the upper levels, the intensification of the mid-Pacific trough is observed at the same stage.