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521 results on '"Held, Isaac M."'

5. Non-Uniqueness in ITCZ Latitude Due To Radiation-Circulation Coupling in an Idealized GCM

Author

Agencia Estatal de Investigación (España), Zurita-Gotor, Pablo [0000-0002-6873-7645], Held, Isaac M. [0000-0002-6744-439X], Merlis, Timothy M. [0000-0002-5593-8210], Chang, Chiung Yin [0009-0009-8815-893X], Hill, Spencer A. [0000-0001-8672-0671], Zurita-Gotor, Pablo, Held, Isaac M., Merlis, Timothy M., Chang, Chiung Yin, Hill, Spencer A., MacDonald, Cameron G., Agencia Estatal de Investigación (España), Zurita-Gotor, Pablo [0000-0002-6873-7645], Held, Isaac M. [0000-0002-6744-439X], Merlis, Timothy M. [0000-0002-5593-8210], Chang, Chiung Yin [0009-0009-8815-893X], Hill, Spencer A. [0000-0001-8672-0671], Zurita-Gotor, Pablo, Held, Isaac M., Merlis, Timothy M., Chang, Chiung Yin, Hill, Spencer A., and MacDonald, Cameron G.

Abstract

An idealized aquaplanet moist global atmospheric model with realistic radiative transfer but no clouds and no convective parameterization is found to possess multiple climate equilibria. When forced symmetrically about the equator, in some cases the Inter Tropical Convergence Zone (ITCZ) migrates to an off-equatorial equilibrium position. Mechanism denial experiments prescribing relative humidity imply that radiation-circulation coupling is essential to this instability. The cross-equatorial asymmetry occurs only when the underlying slab ocean is sufficiently deep and the atmosphere's spectral dynamical core is sufficiently coarse (∼T170 or less with our control parameters). At higher resolutions, initializing with an asymmetric state indicates metastability with very slow (thousands of days) return to hemispheric symmetry. There is some sensitivity to the model timestep, which affects the time required to transition to the asymmetric state, with little effect on the equilibrium climate. The instability is enhanced when the planetary boundary layer scheme favors deeper layers or by a prescribed meridional heat transport away from the equator within the slab. The instability is not present when the model is run with a convective parameterization scheme commonly utilized in idealized moist models. We argue that the instability occurs when the asymmetric heating associated with a spontaneous ITCZ shift drives a circulation that rises poleward of the perturbed ITCZ. These results serve as a warning of the potential for instability and non-uniqueness of climate that may complicate studies with idealized models of the tropical response to perturbations in forcing.

Published
2023

11. A Scaling Theory for Horizontally Homogeneous, Baroclinically Unstable Flow on a Beta-Plane

Author

Held, Isaac M. and Larichev, Vitaly D.

Subjects
Physics - Atmospheric and Oceanic Physics
Abstract

The scaling argument developed by Larichev and Held (1995) for eddy amplitudes and fluxes in a horizontally homogeneous, two-layer model on an f-plane is extended to a beta-plane. In terms of the non-dimensional number x = U/(beta*lambda^2), where lambda is the deformation radius and U is the mean thermal wind, the result for the RMS eddy velocity V, the characteristic wavenumber of the energy-containing eddies and of the eddy-driven jets k, and the magnitude of the eddy diffusivity for potential vorticity D, in the limit x>>1, are as follows: V/U ~ x ; k*lambda ~ 1/x ; D/(U*lambda) ~ x^2. Numerical simulations provide qualitative support for this scaling, but suggest that it underestimates the sensitivity of these eddy statistics to the value of x. A generalization that is applicable to continuous stratification is suggested which leads to the estimates: V ~ 1/(beta T^2); k ~ beta*T; D ~ 1/{[beta^2][T^3]} where T is a time-scale determined by the environment; in particular, it equals lambda/U in the two-layer model and N/(fS) in a continuous flow with uniform shear S and stratification N. This same scaling has also been suggested as relevant to a continuously stratified fluid in the opposite limit, x<<1 (Held, 1980). Therefore, we suggest that it may be of general relevance in planetary atmospheres and in the oceans., Comment: Submitted to Journal of the Atmospheric Sciences. Latex source file. Figures are included in an uuencoded file. Revision only involves submission format, not content of paper. User may wish to obtain postscript version of full paper from http://www.gfdl.gov/~ih

Published
1995
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13. Kinetic energy-conserving hyperdiffusion can improve low resolution atmospheric models

Author

Zurita Gotor, Pablo, Held, Isaac M., Jansen, Malte F., Zurita Gotor, Pablo, Held, Isaac M., and Jansen, Malte F.

Abstract

© 2015. The Authors. © 2015 American Geophysical Union. P.Z.G is funded by grant CGL2012-30641 by the Ministry of Economy and Research of Spain. The results presented in this work were obtained using the spectral dynamical core available at http://www.gfdl.noaa.gov/fms and the kinetic energy-conserving subgrid scheme described in the manuscript. The output data for all simulations in the paper are stored in the Geophysical Fluid Dynamics Laboratory archive system and can be obtained from the first author (pzurita@alum.mit.edu) upon request. We are grateful to Ed Gerber and an anonymous reviewer for their thorough reviews and pertinent suggestions., Motivated by findings that energetically consistent subgrid dissipation schemes can improve eddy-permitting ocean simulations, this work investigates the impact of the subgrid dissipation scheme on low-resolution atmospheric dynamical cores. A kinetic energy-conserving dissipation scheme is implemented in the model adding a negative viscosity term that injects back into the eddy field the kinetic energy dissipated by horizontal hyperdiffusion. The kinetic energy-conserving scheme enhances numerical convergence when horizontal resolution is changed with fixed vertical resolution and gives superior low-resolution results. Improvements are most obvious for eddy kinetic energy but also found in other fields, particularly with strong or little scale-selective horizontal hyperdiffusion. One advantage of the kinetic energy-conserving scheme is that it reduces the sensitivity of the model to changes in the subgrid dissipation rate, providing more robust results., Ministerio de Economia y Competitividad (MINECO), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Published
2023

15. Data files for the manuscript 'Non-uniqueness in ITCZ latitude due to radiation-circulation coupling in an idealized GCM'

Author

Zurita-Gotor, Pablo, Held, Isaac M., Merlis, Timothy M., Chiung-Yin Chang, Hill, Spencer A., and MacDonald, Cameron G.

Abstract

MATLAB scripts and data used to create the figures in the paper "Non-uniqueness in ITCZ latitude due to radiation-circulation coupling in an idealized GCM" by Zurita-Gotor et al., submitted to JAMES., P. Zurita-Gotor is supported by the Spanish Research Agency project DYNWARM (PID2019-109107GB-I00). S. Hill acknowledges funding support from NSF award AGS 2123327.

Published
2023
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32. The Dynamical Core, Physical Parameterizations, and Basic Simulation Characteristics of the Atmospheric Component AM3 of the GFDL Global Coupled Model CM3

Author

Donner, Leo J., Wyman, Bruce L., Hemler, Richard S., Horowitz, Larry W., Ming, Yi, Zhao, Ming, Golaz, Jean-Christophe, Ginoux, Paul, Lin, S.-J., Schwarzkopf, M. Daniel, Austin, John, Alaka, Ghassan, Cooke, William F., Delworth, Thomas L., Freidenreich, Stuart M., Gordon, C. T., Griffies, Stephen M., Held, Isaac M., Hurlin, William J., Klein, Stephen A., Knutson, Thomas R., Langenhorst, Amy R., Lee, Hyun-Chul, Lin, Yanluan, Magi, Brian I., Malyshev, Sergey L., Milly, P. C. D., Naik, Vaishali, Nath, Mary J., Pincus, Robert, Ploshay, Jeffrey J., Ramaswamy, V., Seman, Charles J., Shevliakova, Elena, Sirutis, Joseph J., Stern, William F., Stouffer, Ronald J., Wilson, R. John, Winton, Michael, Wittenberg, Andrew T., and Zeng, Fanrong

Published
2011

50. GFDL’s CM2 Global Coupled Climate Models. Part I : Formulation and Simulation Characteristics

Author

Delworth, Thomas L., Broccoli, Anthony J., Rosati, Anthony, Stouffer, Ronald J., Balaji, V., Beesley, John A., Cooke, William F., Dixon, Keith W., Dunne, John, Dunne, K. A., Durachta, Jeffrey W., Findell, Kirsten L., Ginoux, Paul, Gnanadesikan, Anand, Gordon, C. T., Griffies, Stephen M., Gudgel, Rich, Harrison, Matthew J., Held, Isaac M., Hemler, Richard S., Horowitz, Larry W., Klein, Stephen A., Knutson, Thomas R., Kushner, Paul J., Langenhorst, Amy R., Lee, Hyun-Chul, Lin, Shian-Jiann, Lu, Jian, Malyshev, Sergey L., Milly, P. C. D., Ramaswamy, V., Russell, Joellen, Schwarzkopf, M. Daniel, Shevliakova, Elena, Sirutis, Joseph J., Spelman, Michael J., Stern, William F., Winton, Michael, Wittenberg, Andrew T., Wyman, Bruce, Zeng, Fanrong, and Zhang, Rong

Published
2006

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