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Marcus, S. L.

Publications and source records attributed to Marcus, S. L..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Detection of an ENSO Signal in Seasonal Atmospheric Angular Momentum Varitations

None. From Intro list: Investigate use of Earth rotation measurements as proxy measures of atmospheric angular momentum in global climate change studies. Examine role of observed length-of-day changes. Study observed changes in strength of seasonal lod signal. Investigate origin of this correlation by examining angular momentum of NCEP zonal winds.

angular momentum global climate change climate cha↗
NASA NTRS1996

Atmospheric Angular Momentum Fluctuations in Global Circulation Models During the Period 1979-1988

...A stringent test of any numerical global circulation model (GCM) is therefore provided by a quantitative assessment of its ability to represent AAM fluctuations on all relevant time scales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme (WCRP), we have investigated seasonal and interanual fluctuations and the decadal means are generally well simulated.

Earth's↗
NASA NTRS1994

Angular momentum exchange among the solid Earth, atmosphere, and oceans: A case study of the 1982-1983 El Nino event

The 1982-1983 El Nino/Southern Oscillation (ENSO) event was accompanied by the largest interannual variation in the Earth's rotation rate on record. In this study we demonstrate that atmospheric forcing was the dominant cause for this rotational anomaly, with atmospheric angular momentum (AAM) integrated from 1000 to 1 mbar (troposphere plus stratosphere) accounting for up to 92% of the interannual variance in the length of day (LOD). Winds between 100 and 1 mbar contributed nearly 20% of the variance explained, indicating that the stratosphere can play a significant role in the Earth's angular momentum budget on interannual time scales. Examination of LOD, AAM, and Southern Oscillation Index (SOI) data for a 15-year span surrounding the 1982-1983 event suggests that the strong rotational response resulted from constructive interference between the low-frequency (approximately 4-6 year) and quasi-biennial (approximately 2-3 year) components of the ENSO phenomenon, as well as the stratospheric Quasi-Biennial Oscillation (QBO). Sources of the remaining LOD discrepancy (approximately 55 and 64 microseconds rms residual for the European Centre for Medium-Range Forecasting (EC) and U.S. National Meteorological Center (NMC) analyses) are explored; noise and systematic errors in the AAM data are estimated to contribute 18 and 33 microseconds, respectively, leaving a residual (rms) of 40 (52) microseconds unaccounted for by the EC (NMC) analysis. Oceanic angular momentum contributions (both moment of inertia changes associated with baroclinic waves and motion terms) are shown to be candidates in closing the interannual axial angular momentum budget.

Dickey, J. O.↗
NASA NTRS1994

The extratropical 40-day oscillation in the UCLA general circulation model. Part 1: Atmospheric angular momentum

Variations in atmospheric angular momentum (AAM) are examined in a three-year simulation of the large-scale atmosphere with perpetual January forcing. The simulation is performed with a version of the University of California at Los Angeles (UCLA) general circulation model that contains no tropical Madden-Julian Oscillation (MJO). In addition, the results of three shorter experiments with no topography are analyzed. The three-year standard topography run contains no significant intraseasonal AAM periodicity in the tropics, consistent with the lack of the MJO, but produces a robust, 42-day AAM oscillation in the Northern Hemisphere (NH) extratropics. The model tropics undergoes a barotropic, zonally symmetric oscillation, driven by an exchange of mass with the NH extratropics. No intraseasonal periodicity is found in the average tropical latent heating field, indicating that the model oscillation is dynamically rather than thermodynamically driven. The no-mountain runs fail to produce an intraseasonal AAM oscillation, consistent with a topographic origin for the NH extratropical oscillation in the standard model. The spatial patterns of the oscillation in the 500-mb height field, and the relationship of the extratropical oscillation to intraseasonal variations in the tropics, will be discussed in Part 2 of this study.

Marcus, S. L.↗
NASA NTRS1993

The oceanic contribution to the Earth's seasonal angular momentum budget

Seasonal variations in the speed of the Earth's rotation manifest themselves as fluctuations in the length of the day (LOD) with an amplitude of about 1000 microseconds. We know from previous work that at least 95% of these variations can be accounted for in terms of angular momentum exchanged between the atmosphere and the solid Earth. Here we examine the respective contributions of the Antarctic Circumpolar Current (ACC) and the global oceans to the Earth's seasonal angular momentum budget, using in situ data from the Drake Passage and results from both the oceanic regional model (Fine Resolution Antarctic Model -- FRAM) of Webb et al. (1991) and the global ocanic model of Maier-Reimer et al. (1993) as analyzed by Brosche et al. (1990). The estimated annual contribution of the ACC (2-4 microsec) is much smaller than the total variation in the oceanic models or the existing LOD-AAM residual (both approximately 15-20 microsec). The estimated semi-annual ACC contribution (3-8 microsec) is offset by counter-current further north in both oceanic models, which exhibit larger semi-annual variations in planetary angular momentum. Further refinements in the Earth's seasonal angular momentum budget, therefore, will require the full (planetary plus relative) contribution of the global oceans in addition to that of the ACC.

Dickey, J. O.↗
NASA NTRS1993

Determination of the Excess Length-of-Day Since 1630

The Kalman Earth Orientation Filter (KEOF) is used at JPL to combine independent observations of the Earth's rotation parameters, producing smoothed, interpolated estimates of polar motion (PM) and UT1-TAI, as well as estimates of their excitation functions such as the length-of-day (lod). Prior to their combination, adjustments to the data sets are made in order to place them within a common reference frame. Recently, a number of lod data sets have been determined at JPL by combining the observations summarized in Table 1. The resulting lod data sets, summarized in Table 2, span different time intervals depending upon the particular subset of observations being combined, with the longest series, spanning 1630-1990, being obtained by combining all of the observations. The determination of these lod data sets and their comparison with series of climate indicators such as the Southern Oscillation Index will be discussed.

Gross, R. S.↗
NASA NTRS1993

Earth Rotation and Global Change

Global climate change, whether from natural or man-made causes, can be expected to lead to changes in the Earth's rotation. General Circulation Models (GCMs) of the atmosphere that have been used to study the effects of changes in the amount of atmospheric greenhouse gasses general predict the globally averaged temperature to increase by 1 degree to 4 degrees C during the next century. This temperature increase is not expected to occur uniformly over the globe, but should exhibit regional variations. This changing atmospheric temperature field will cause changes in the atmospheric wind field and hence in the atmospheric angular momentum (AAM). Since the angular momentum of the atmosphere-solid Earth system is conserved, a thermally-induced change in the AAM will cause consequent changes in the rotation of the solid Earth...

Dickey, J. O.↗