Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales
The two leading empirical orthogonal functions (EOFs) of zonal-mean zonal wind describe north-south fluctuations, and intensification and narrowing, respectively, of the midlatitude jet. Under certain circumstances, these two leading EOFs cannot be regarded as independent but are in fact manifestati...
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| Format: | Article |
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American Meteorological Society
2018
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| Online Access: | http://hdl.handle.net/1721.1/114585 https://orcid.org/0000-0002-6716-1576 |
| _version_ | 1811082209246838784 |
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| author | Sheshadri, Aditi Plumb, R. Alan |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Sheshadri, Aditi Plumb, R. Alan |
| author_sort | Sheshadri, Aditi |
| collection | MIT |
| description | The two leading empirical orthogonal functions (EOFs) of zonal-mean zonal wind describe north-south fluctuations, and intensification and narrowing, respectively, of the midlatitude jet. Under certain circumstances, these two leading EOFs cannot be regarded as independent but are in fact manifestations of a single, coupled, underlying mode of the dynamical system describing the evolution in time of zonal wind anomalies. The true modes are revealed by the principal oscillation patterns (POPs). The leading mode and its associated eigenvalue are complex, its structure involves at least two EOFs, and it describes poleward (or equatorward) propagation of zonal-mean zonal wind anomalies. In this propagating regime, the principal component (PC) time series associated with the two leading EOFs decay nonexponentially, and the response of the system to external forcing in a given EOF does not depend solely on the PC decorrelation time nor on the projection of the forcing onto that EOF. These considerations are illustrated using results from an idealized dynamical core model. Results from Southern Hemisphere ERA-Interim data are partly consistent with the behavior of the model's propagating regime. Among other things, these results imply that the time scale that determines the sensitivity of a model to external forcing might be different from the decorrelation time of the leading PC and involves both the rate of decay of the dynamical mode and the period associated with propagation. Keywords: Annular mode; Atmospheric circulation; Dynamics |
| first_indexed | 2024-09-23T11:59:26Z |
| format | Article |
| id | mit-1721.1/114585 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T11:59:26Z |
| publishDate | 2018 |
| publisher | American Meteorological Society |
| record_format | dspace |
| spelling | mit-1721.1/1145852024-05-15T07:33:28Z Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales Sheshadri, Aditi Plumb, R. Alan Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Plumb, Raymond Alan The two leading empirical orthogonal functions (EOFs) of zonal-mean zonal wind describe north-south fluctuations, and intensification and narrowing, respectively, of the midlatitude jet. Under certain circumstances, these two leading EOFs cannot be regarded as independent but are in fact manifestations of a single, coupled, underlying mode of the dynamical system describing the evolution in time of zonal wind anomalies. The true modes are revealed by the principal oscillation patterns (POPs). The leading mode and its associated eigenvalue are complex, its structure involves at least two EOFs, and it describes poleward (or equatorward) propagation of zonal-mean zonal wind anomalies. In this propagating regime, the principal component (PC) time series associated with the two leading EOFs decay nonexponentially, and the response of the system to external forcing in a given EOF does not depend solely on the PC decorrelation time nor on the projection of the forcing onto that EOF. These considerations are illustrated using results from an idealized dynamical core model. Results from Southern Hemisphere ERA-Interim data are partly consistent with the behavior of the model's propagating regime. Among other things, these results imply that the time scale that determines the sensitivity of a model to external forcing might be different from the decorrelation time of the leading PC and involves both the rate of decay of the dynamical mode and the period associated with propagation. Keywords: Annular mode; Atmospheric circulation; Dynamics Simons Foundation (Award 354584) National Science Foundation (U.S.) (Grant OCE-1338814) 2018-04-06T14:21:01Z 2018-04-06T14:21:01Z 2017-04 2017-01 2018-03-30T17:46:38Z Article http://purl.org/eprint/type/JournalArticle 0022-4928 1520-0469 http://hdl.handle.net/1721.1/114585 Sheshadri, Aditi, and R. Alan Plumb. “Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales.” Journal of the Atmospheric Sciences 74, 5 (May 2017): 1345–1361 © 2017 American Meteorological Society https://orcid.org/0000-0002-6716-1576 http://dx.doi.org/10.1175/JAS-D-16-0291.1 Journal of the Atmospheric Sciences Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Meteorological Society American Meteorological Society |
| spellingShingle | Sheshadri, Aditi Plumb, R. Alan Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title | Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title_full | Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title_fullStr | Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title_full_unstemmed | Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title_short | Propagating Annular Modes: Empirical Orthogonal Functions, Principal Oscillation Patterns, and Time Scales |
| title_sort | propagating annular modes empirical orthogonal functions principal oscillation patterns and time scales |
| url | http://hdl.handle.net/1721.1/114585 https://orcid.org/0000-0002-6716-1576 |
| work_keys_str_mv | AT sheshadriaditi propagatingannularmodesempiricalorthogonalfunctionsprincipaloscillationpatternsandtimescales AT plumbralan propagatingannularmodesempiricalorthogonalfunctionsprincipaloscillationpatternsandtimescales |