Publications by Type: Journal Article

2005
Kondrashov, Dmitri, Yizhak Feliks, and Michael Ghil. 2005. “Oscillatory modes of extended Nile River records (A.D. 622–1922).” Geophysical Research Letters 32 (10). AGU: L10702. Abstract

The historical records of the low- and high-water levels of the Nile River are among the longest climatic records that have near-annual resolution. There are few gaps in the first part of the records (A.D. 622-1470) and larger gaps later (A.D. 1471-1922). We apply advanced spectral methods, Singular-Spectrum Analysis (SSA) and the Multi-Taper Method (MTM), to fill the gaps and to locate interannual and interdecadal periodicities. The gap filling uses a novel, iterative version of SSA. Our analysis reveals several statistically significant features of the records: a nonlinear, data-adaptive trend that includes a 256-year cycle, a quasi-quadriennial (4.2-year) and a quasi-biennial (2.2-year) mode, as well as additional periodicities of 64, 19, 12, and, most strikingly, 7 years. The quasi-quadriennial and quasi-biennial modes support the long-established connection between the Nile River discharge and the El-Niño/Southern Oscillation (ENSO) phenomenon in the Indo-Pacific Ocean. The longest periods might be of astronomical origin. The 7-year periodicity, possibly related to the biblical cycle of lean and fat years, seems to be due to North Atlantic influences.

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Ghil, Michael, Tian Ma, and Shouhong Wang. 2005. “Structural Bifurcation of 2-D Nondivergent Flows with Dirichlet Boundary Conditions: Applications to Boundary-Layer Separation.” SIAM J. Appl. Math. 65 (5). Society for Industrial & Applied Mathematics (SIAM): 1576–1596.
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2004
Feliks, Yizhak, Michael Ghil, and Eric Simonnet. 2004. “Low-frequency variability in the midlatitude atmosphere induced by an oceanic thermal front.” Journal of the atmospheric sciences 61 (9): 961–981.
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Feliks, Yizhak, Michael Ghil, and Eric Simonnet. 2004. “Low-frequency variability in the midlatitude atmosphere induced by an oceanic thermal front.” Journal of the Atmospheric Sciences 61 (9): 961–981. Abstract
This study examines the flow induced in a highly idealized atmospheric model by an east–west-oriented oceanic thermal front. The model has a linear marine boundary layer coupled to a quasigeostrophic, equivalent- barotropic free atmosphere. The vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet, parallel to the oceanic front's isotherms. A large gyre develops on either side of this jet, cyclonic to the north and anticyclonic to the south of it. As the jet intensifies during spinup from rest, it becomes unstable. The most unstable wave has a length of about 500 km, it evolves into a meander, and eddies detach from the eastern edge of each gyre. The dependence of the atmospheric dynamics on the strength T of the oceanic front is studied. The Gulf Stream and Kuroshio fronts correspond roughly, in the scaling used here, to T 7°C. For weak fronts, T < 4°C, the circulation is steady and exhibits two large, antisymmetric gyres separated by a westerly zonal jet. As the front strengthens, 4 < T < 5, the solution undergoes Hopf bifurcation to become periodic in time, with a period of 30 days, and spatially asymmetric. The bifurcation is due to the westerly jet's barotropic instability, which has a symmetric spatial pattern. The addition of this pattern to the antisymmetric mean results in the overall asymmetry of the full solution. The spatial scale and amplitude of the symmetric, internally generated, and antisymmetric, forced mode increase with the strength T of the oceanic front. For T > 5°C, the solution becomes chaotic, but a dominant period still stands out above the broadband noise. This dominant period increases with T overall, but the increase is not monotonic. The oceanic front's intensity dictates the mean speed of the atmospheric jet. Two energy regimes are obtained. 1) In the low-energy regime, the SST front, and hence the atmospheric jet, are weak; in this regime, small meanders develop along the jet axis, and the dominant period is about 25 days. 2) In the high-energy regime, the SST front and the jet are strong; in it, large meanders and eddies develop along the jet, and the dominant oscillation has a period of about 70 days. The physical nature of the two types of oscillations is discussed, as are possible transitions between them when T changes on very long time scales. The results are placed in the context of previous theories of ocean front effects on atmospheric flows, in which baroclinic phenomena are dominant.
Ghil, Michael, Jian-Guo Liu, Cheng Wang, and Shouhong Wang. 2004. “Boundary-layer separation and adverse pressure gradient for 2-D viscous incompressible flow.” Physica D: Nonlinear Phenomena 197 (1-2). Elsevier BV: 149–173.
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Kao, Jim, Dawn Flicker, Rudy Henninger, Sarah Frey, Michael Ghil, and Kayo Ide. 2004. “Data assimilation with an extended Kalman filter for impact-produced shock-wave dynamics.” Journal of Computational Physics 196 (2). Elsevier: 705–723.
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Kravtsov, Sergey, and Michael Ghil. 2004. “Interdecadal variability in a hybrid coupled ocean-atmosphere-sea ice model.” Journal of Physical Oceanography 34 (7): 1756–1775.
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Loeuille, Nicolas, and Michael Ghil. 2004. “Intrinsic and climatic factors in North-American animal population dynamics.” BMC Ecology 4 (1). BioMed Central: 1. Publisher's Version
Lott, François, Andrew W. Robertson, and Michael Ghil. 2004. “Mountain torques and Northern Hemisphere low-frequency variability. Part II: Regional aspects.” Journal of the Atmospheric Sciences 61 (11): 1272–1283.
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Lott, François, Andrew W. Robertson, and Michael Ghil. 2004. “Mountain torques and Northern Hemisphere low-frequency variability. Part I: Hemispheric aspects.” Journal of the Atmospheric Sciences 61 (11): 1259–1271.
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Sayag, Roiy, Eli Tziperman, and Michael Ghil. 2004. “Rapid switch-like sea ice growth and land ice–sea ice hysteresis.” Paleoceanography 19 (1). Wiley Online Library.
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Kahn, Brian H., Annmarie Eldering, Michael Ghil, Simona Bordoni, and Shepard A. Clough. 2004. “Sensitivity analysis of cirrus cloud properties from high-resolution infrared spectra. Part I: Methodology and synthetic cirrus.” Journal of Climate 17 (24): 4856–4870.
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Kondrashov, Dmitri, K. Ide, and Michael Ghil. 2004. “Weather regimes and preferred transition paths in a three-level quasigeostrophic model.” Journal of the Atmospheric Sciences 61 (5): 568–587.
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2003
Zaliapin, Ilya, Vladimir Keilis-Borok, and Michael Ghil. 2003. “A Boolean delay equation model of colliding cascades. Part I: Multiple seismic regimes.” Journal of Statistical Physics 111 (3-4). Springer: 815–837.
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Zaliapin, Ilya, Vladimir Keilis-Borok, and Michael Ghil. 2003. “A Boolean delay equation model of colliding cascades. Part II: Prediction of critical transitions.” Journal of Statistical Physics 111 (3-4). Springer: 839–861.
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Ghil, Michael. 2003. “Did celestial chaos kill the dinosaurs?” The Observatory 123 (1177): 328–333.
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Simonnet, Eric, Michael Ghil, Shouhong Wang, and Zhi-Min Chen. 2003. “Hopf Bifurcation in Quasi-geostrophic Channel Flow.” SIAM J. Appl. Math. 64 (1). Society for Industrial & Applied Mathematics (SIAM): 343–368.
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Bellon, G., H. Le Treut, and Michael Ghil. 2003. “Large-scale and evaporation-wind feedbacks in a box model of the tropical climate.” Geophysical Research Letters 30 (22). Wiley Online Library.
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Kravtsov, S., Andrew W. Robertson, and Michael Ghil. 2003. “Low-Frequency Variability in a Baroclinic Beta-Channel with Land-Sea Contrast*.” Journal of the Atmospheric Sciences 60 (18): 2267–2293.
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Simonnet, Eric, Michael Ghil, Kayo Ide, Roger Temam, and Shouhong Wang. 2003. “Low-frequency variability in shallow-water models of the wind-driven ocean circulation. Part II: Time-dependent solutions.” Journal of Physical Oceanography 33 (4). Abstract

The time-dependent wind-driven ocean circulation is investigated for both a rectangular and a North Atlantic– shaped basin. Multiple steady states in a 2 ½ -layer shallow-water model and their dependence on various pa- rameters and other model properties were studied in Part I for the rectangular basin. As the wind stress on the rectangular basin is increased, each steady-state branch is destabilized by a Hopf bifurcation. The periodic solutions that arise off the subpolar branch have a robust subannual periodicity of 4–5 months. For the subtropical branch, the period varies between sub- and interannual, depending on the inverse Froude number F 2 defined with respect to the lower active layer’s thickness H 2 . As F 2 is lowered, the perturbed-symmetric branch is destabilized baroclinically, before the perturbed pitchfork bifurcation examined in detail in Part I occurs. Transition to aperiodic behavior arises at first by a homoclinic explosion off the isolated branch that exists only for sufficiently high wind stress. Subsequent global and local bifurcations all involve the subpolar branch, which alone exists in the limit of vanishing wind stress. Purely subpolar solutions vary on an interannual scale, whereas combined subpolar and subtropical solutions exhibit complex transitions affected by a second, subpolar homoclinic orbit. In the latter case, the timescale of the variability is interdecadal. The role of the global bifurcations in the interdecadal variability is investigated. Numerical simulations were carried out for the North Atlantic with earth topography- 5 minute (ETOPO-5) coastline geometry in the presence of realistic, as well as idealized, wind stress forcing. The simulations exhibit a realistic Gulf Stream at 20-km resolution and with realistic wind stress. The variability at 12-km resolution exhibits spectral peaks at 6 months, 16 months, and 6–7 years. The subannual mode is strongest in the subtropical gyre; the interannual modes are both strongest in the subpolar gyre.

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