Extratropical aspects of the 40–50 day oscillation in length‐of‐day and atmospheric angular momentum

Dickey, J. O.; Ghil, Michael; Marcus, S. L.

doi:10.1029/91jd02339

Cited by 71 publications

(57 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There is some evidence that the mid-latitude circulation over the North Pacific is correlated to convective anomalies associated with the tropical oscillation (56,62,63). On the other hand, Dickey et al (55) and Ghil and Mo (57) found the extratropical mode to be often independent of, and sometimes to lead, the tropical one. Upper-level potential vorticity anomalies are known to propagate from the mid-latitudes into the tropics; this propagation is associated with NW-SE tilting troughs (64).…”

Section: Markov Chains Transition Matricesmentioning

confidence: 95%

“…The careful analysis of perpetual-January runs with an atmospheric GCM thus confirms, on the one hand, the topographic origin of the NH 40-day oscillation, originally suggested by simple-and intermediate-model studies (6,58,59,67,75). On the other, it provides greater realism and spatio-temporal detail, permitting therewith a much better confrontation of the theory with the existing observations (55,57).…”

Section: Gcm Simulations and Their Validationmentioning

confidence: 99%

See 1 more Smart Citation

“Waves” vs. “particles” in the atmosphere's phase space: A pathway to long-range forecasting?

Ghil

Robertson

2002

Proc. Natl. Acad. Sci. U.S.A.

170

169

View full text Add to dashboard Cite

Thirty years ago, E. N. Lorenz provided some approximate limits to atmospheric predictability. The details-in space and time-of atmospheric flow fields are lost after about 10 days. Certain gross flow features recur, however, after times of the order of 10 -50 days, giving hope for their prediction. Over the last two decades, numerous attempts have been made to predict these recurrent features. The attempts have involved, on the one hand, systematic improvements in numerical weather prediction by increasing the spatial resolution and physical faithfulness in the detailed models used for this prediction. On the other hand, theoretical attempts motivated by the same goal have involved the study of the large-scale atmospheric motions' phase space and the inhomogeneities therein. These ''coarse-graining'' studies have addressed observed as well as simulated atmospheric data sets. Two distinct approaches have been used in these studies: the episodic or intermittent and the oscillatory or periodic. The intermittency approach describes multiple-flow (or weather) regimes, their persistence and recurrence, and the Markov chain of transitions among them. The periodicity approach studies intraseasonal oscillations, with periods of 15-70 days, and their predictability. We review these two approaches, ''particles'' vs. ''waves,'' in the quantum physics analogy alluded to in the title of this article, discuss their complementarity, and outline unsolved problems.

show abstract

Section: Markov Chains Transition Matricesmentioning

confidence: 95%

Section: Gcm Simulations and Their Validationmentioning

confidence: 99%

“Waves” vs. “particles” in the atmosphere's phase space: A pathway to long-range forecasting?

Ghil

Robertson

2002

Proc. Natl. Acad. Sci. U.S.A.

170

169

View full text Add to dashboard Cite

show abstract

“…Among them are the low-frequency oscillations with periods of 40-50 days, which were first detected in tropical convection and zonal winds (Madden & Julian 1971, 1972, and were also found later by analysis of length-of-day and atmospheric angular momentum data (Langley, King & Shapiro 1981). More detailed observational studies (Anderson & Rosen 1983;Dickey, Ghil & Marcus 1991) have identified a significant contribution to such oscillations from the Northern Hemisphere extratropics.…”

Section: Introductionmentioning

confidence: 96%

“…Our fluid is isothermal and incompressible, and the rigid side, top, and bottom walls of our annular container differ from the atmosphere's boundaries. To help understand the laboratory results and connect them with numerical models of the atmosphere (Charney & DeVore 1979;Pedlosky 1981;Legras & Ghil 1985;Jin & Ghil 1990) and with observations (Dickey et al 1991;Ghil & Mo 1991;Lott, Robertson & Ghil 2001), we constructed a numerical model to simulate the annulus experiment. The model is governed by the quasi-geostrophic (QG) barotropic potential vorticity equation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical studies of an eastward jet over topography

et al. 2001

View full text Add to dashboard Cite

Motivated by the phenomena of blocked and zonal flows in Earth's atmosphere, we conducted laboratory experiments and numerical simulations to study the dynamics of an eastward jet flowing over wavenumber-two topography. The laboratory experiments studied the dynamical behaviour of the flow in a barotropic rotating annulus as a function of the experimental Rossby and Ekman numbers. Two distinct flow patterns, resembling blocked and zonal flows in the atmosphere, were observed to persist for long time intervals.Earlier model studies had suggested that the atmosphere's normally upstreampropagating Rossby waves can resonantly lock to the underlying topography, and that this topographic resonance separates zonal from blocked flows. In the annulus, the zonal flows did indeed have super-resonant mean zonal velocities, while the blocked flows appear subresonant. Low-frequency variability, periodic or irregular, was present in the measured time series of azimuthal velocity in the blocked regime, with dominant periodicities in the range of 6-25 annulus rotations. Oscillations have also been detected in zonal states, with smaller amplitude and similar frequency. In addition, over a large region of parameter space the two flow states exhibited spontaneous, intermittent transitions from the one to the other.We numerically simulated the laboratory flow geometry in a quasi-geostrophic barotropic model over a similar range of parameters. Both flow regimes, blocked and zonal, were reproduced in the simulations, with similar spatial and temporal characteristics, including the low-frequency oscillations associated with the blocked flow. The blocked and zonal flow patterns are present over wide ranges of forcing, topographic height, and bottom friction. For a significant portion of parameter space, both model flows are stable. Depending on the initial state, either the blocked or the zonal flow is obtained and persists indefinitely, showing the existence of multiple equilibria.

show abstract

“…However, let us note that equatorward modes have also been shown in the case of the much more rapid subseasonal MaddenJulian oscillations in AAM by Dickey et al (1991). The origin of both could be related to mobile polar highs (MPH) (Leroux, 1993), which may originate in the downward air motion in the polar latitudes, before moving equatorward.…”

Section: Zonal Analysismentioning

confidence: 99%

Interannual signals in length of day and atmospheric angular momentum

Río¹,

Gambis

Salstein

2000

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. Atmospheric angular momentum (AAM) and length of day (LOD) series are investigated for their characteristics on interannual time scales during the half-century period 1949 to 1998. During this epoch, the interannual variability in LOD can be separated naturally into three bands: a quasi-biennial, a triennialquadrennial and one at six-seven years. The atmosphere appears to excite the ®rst two bands, while it does not contribute to the last. Considering the quasi-biennial (QB) band alone, the atmosphere appears to excite most of its signal in LOD, but it arises from separatē uctuations with stratospheric and tropospheric origin. Thus, although close in frequency, stratospheric and tropospheric processes dier in their amplitude and phase variability. The time shift can be noted especially during the strong El NinÄ o events of 1982±83 and 1997± 98 when both processes have positive phase and thus combine to help produce particularly strong peak in AAM and LOD. In addition, we have recon®rmed the downward propagation in the stratosphere and upward propagation in the troposphere of AAM observed in earlier studies for other variables. In the triennialquadrennial (TQ) band, time-variable spectral analyses reveal that LOD and AAM contain strong variability, with periods shorter than four years before 1975 and longer thereafter. This signal originates mainly within the troposphere and propagates upwards from the lower to the higher layers of the troposphere. According to a zonal analysis, an equatorial poleward mode, strongly linked to the SOI, explains more than 60% of the total variability at these ranges. In addition, this study also indicates that an equatorward mode, originating within polar latitudes, explains, on average, more than 15% of the triennial-quadrennial oscillation (TQO) variability in AAM, and up to 30% at certain epochs. Finally, a six year period in LOD noted in earlier studies, as well as in lengthier series covering much of the century, is found to be absent in atmospheric excitations, and it is thus likely to arise from mantle/core interactions.

show abstract

Extratropical aspects of the 40–50 day oscillation in length‐of‐day and atmospheric angular momentum

Cited by 71 publications

References 63 publications

“Waves” vs. “particles” in the atmosphere's phase space: A pathway to long-range forecasting?

“Waves” vs. “particles” in the atmosphere's phase space: A pathway to long-range forecasting?

Experimental and numerical studies of an eastward jet over topography

Interannual signals in length of day and atmospheric angular momentum

Contact Info

Product

Resources

About