Evidence for an angular momentum flux in the solar wind
A round table discussion of problems of solar and stellar spindown and theory is presented. Observational evidence of the angular momentum flux of the solar wind is emphasized.
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Annihilation of angular momentum drift during spinning-up and thrusting maneuvers of rigid bodies
A very simple, yet accurate, heuristic solution for the spiral path of the angular momentum vector during spin-up and spin-down maneuvers of rigid body spacecraft is presented. A two-burn scheme is proposed consisting of a burn, a coast, and a second burn of the spin thruster. The appropriate burn times are found by a transcendental equation similar to Kepler's equation. Numerical results verify the accuracy of the burn, coast, and burn times given by closed form expressions. The scheme can also be applied to the problem of axial thrusting during constant spin.
Longuski, J. M.↗
Predictions of zonal wind and angular momentum by the NMC medium-range forecast model during 1985-89
This paper investigates the quality of weather predictions of the atmosphere's relative angular momentum (M) made by the most recent version of the NMC medium-range forecast model (MRF88) during December 1985-1989. It was found that, compared with older versions of MRF, bias errors in the MRF88 forecasts of M became more prominent, while random errors were not affected. Both types of errors in the M forecasts could be traced to problems with forecasts in the zonal mean zonal wind in the tropics.
Rosen, Richard D.↗
Interannual Fluctuations in Atmospheric Angular Momentum Simulated by the National Centers for Environmental Prediction Medium Range Forecast Model
An earlier study established the existence of globally coherent interannual fluctuations in atmospheric angular momentum (AAM), associated with the El Nino-Southern Oscillation (ENSO) cycle. In this paper, we pursue the origin and the structure of these fluctuations using an ensemble of experiments generated by the National Centers for Environmental Prediction, medium range forecast model version 9. In the control experiments, where the observed sea surface temperatures (SSTs) were used as the lower boundary conditions, the model captures the characteristic V-like structure in time-latitude plots of zonally averaged AAM, while experiments with climatological SSTs and those with either perpetual warm or cold ENSO conditions superimposed on the climatological SSTs failed to reproduce this structure. The numerical results indicate that these AAM structures are related to SST variations associated with transitions between different phases of the ENSO cycle and have both propagating and standing components. The largest zonal wind contribution from the levels studied (850, 500, and 200 hPa) is at 200 hPa, where the tropical convective outflow is the strongest. Composites of zonal wind and geopotential height show a clear relationship between the stages of the global AAM oscillation and the ENSO cycle. The strong similarity between the simulated and observed AAM series attests to the model's ability to realistically simulate the interannual response of the atmosphere to ENSO SST anomalies.
Mo, Kingtse C.↗
WGM resonators for studying orbital angular momentum of a photon, and methods
An optical system, device, and method that are capable of generating high-order Bessel beams and determining the orbital angular momentum of at least one of the photons of a Bessel beam are provided. The optical system and device include a tapered waveguide having an outer surface defined by a diameter that varies along a longitudinal axis of the waveguide from a first end to an opposing second end. The optical system and device include a resonator that is arranged in optical communication with the first end of the tapered waveguide such that an evanescent field emitted from (i) the waveguide can be coupled with the resonator, or (ii) the resonator can be coupled with the waveguide.
Matsko, Andrey B.↗
Variations in atmospheric angular momentum and the length of day
Six years of twice daily global analyses were used to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values were compared to independently determined charges in the rotation rate of the solid Earth. Finally, the atmospheric data was examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and which regions are contributing most to the changes found in the global integral. The data and techniques used to derive the time series of momentum values are described.
Rosen, R. D.↗
Principal modes of intraseasonal variations in atmospheric angular momentum and tropical convection
Five-day National Meteorological Center wind and outgoing longwave radiation (OLR) data are used here to study the seasonal, intraseasonal variation of angular momentum and its relationship with tropical convection. It is found that the zonally averaged u component and the zonally averaged OLR show pronounced periodicities around 30-60 days. The globally averaged zonal wind at 250 mbar exhibits strong seasonal variation in connection with the expansion and contraction of the easterly and westerly belt. At upper levels this is manifested as the poleward and equatorward migration of the subtropical jet streams. Results show that the 30- to 60-day oscillation in 250 mbar zonal mean wind and OLR can be represented by three basic meridional structures: tropical modes, tropical-subtropical modes, and extratropical modes.
Lau, K.-M.↗
Modulation of the seasonal cycle in the Earth's atmospheric, oceanic, and mantle angular momentum
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length of day atmospheric angular momentum oceanic↗
Discrepancies in the earth-atmosphere angular momentum budget
Modern geodetic and atmospheric data sets have demonstrated that changes in the solid earth's rotation rate are closely coupled to changes in the atmosphere's angular momentum over a range of subseasonal through interannual time scales. Nevertheless, limits to the correspondence between changes in the momenta of the two bodies exist at both ends of the spectrum resolvable by the data. It is shown that, at high frequencies, changes in the length of day as short as a fortnight can now be attributed almost entirely to atmospheric forcing; more rapid fluctuations in the length of day, however, cannot be shown to coincide with atmospheric behavior, a result blamed mostly on errors remaining in both the geodetic and atmospheric series rather than on the neglect of some other component of the momentum budget. On the decadal time scale, nonatmospheric processes, believed primarily to involve core-mantle coupling, dominate the global momentum budget.
Rosen, Richard D.↗
Rotational excitation in collisions between two rigid rotors - Alternate angular momentum coupling and pressure broadening of HCl by H2
In order to compute relaxation 'cross sections' for molecule-molecule collisions, it is convenient to employ a coupled angular-momentum representation which differs from that generally used. An explicit expression for collision-induced spectral pressure broadening in this representation is given, and this is used to examine the difference between para- and ortho-H2 for broadening of HCl.
Green, S.↗
Medium-range numerical forecasts of atmospheric angular momentum
Forecasts of zonal wind fields produced by the medium-range forecast (MRF) model of the National Meteorological Center are used to create predictions of the atmosphere's angular momentum at lead times of 1-10 days. Based on momentum forecasts archived for the period December 1985-November 1986, it is found that, on average, the MRF exhibits positive skill relative to persistence-based forecasts at all lead times. Over the entire one-year study period, the improvement over persistence exceeds 20 percent for 2-6 day forecasts and remains as large as 10 percent even for 10-day forecasts. On the other hand, skill scores for the MRF momentum predictions vary considerably from month to month, and for a sizable fraction of the study period, the MRF is less skillful than persistence.
Rosen, Richard D.↗
Atmospheric Angular Momentum Fluctuations During 1979-1988 Simulated by Global Circulation Models
Changes in major global dynamical phenomena in the Earth's atmosphere are manifested in the time series of atmospheric angular momentum (AAM), as determined directly from meteorological observations and indirectly from geodetic observations of small fluctuations in the rotation of the solid Earth which are proportional to length of day. AAM fluctuations are intimately linked with energetic processes throughout the whole atmosphere and also with the stresses at the Earth's surface produced largely by turbulent momentum transport in the oceanic and continental boundary layers and by the action of normal pressure forces on orographic features. 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 timescales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme, we have investigated seasonal and interannual fluctuations and the decadal mean in the axial component of AAM in 23 AMIP GCMs over the period 1979-1988. The decadal means are generally well simulated, with the model median value (1.58 x 10(exp 26) kg sq m/s) being only 3.5% larger than the observed mean and with 10 of the models being within 5% of the observed. The seasonal cycle is well reproduced, with the median amplitude of the models seasonal standard deviations being only 2.4% larger than observed. Half the seasonal amplitudes lie within 15% of the observed, and the median correlation found between the observed and model seasonal cycles is 0.95. The dominant seasonal error is an underestimation of AAM during northern hemisphere winter associated with errors in the position of subtropical jets. Less robust are the modeled interannual variations, although the median correlation of 0.61 between model simulations and observed AAM is statistically significant. The two El Nino-Southem Oscillation events that occurred during the AMIP decade 1979-1988 have the expected positive AAM anomalies, although the AAM signature of the 1982-1983 event tends to be underestimated and that of the 1986-1987 event overestimated.
Hide, R.↗
Atmospheric Angular Momentum Fluctuations During 1979-1988 Simulated by Global Circulation Models
Changes in major global dynamical phenomena in the Earth's atmosphere are manifested in the time series of atmospheric angular momentum (AAM), as determined directly from meteorological observations and indirectly from geodetic observations of small fluctuations in the rotation of the solid Earth which are proportional to length of day. AAM fluctuations are intimately linked with energetic processes throughout the whole atmosphere and also with the stresses at the Earth's surface produced largely by turbulent momentum transport in the oceanic and continental boundary layers and by the action of normal pressure forces on orographic features. 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 timescales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme, we have investigated seasonal and interannual fluctuations and the decadal mean in the axial component of AAM in 23 AMIP GCMs over the period 1979-1 988. The decadal means are generally well simulated, with the model median value (1.58 x 10(exp 26) kg sq m/s) being only 3.5% larger than the observed mean and with 10 of the models being within 5% of the observed. The seasonal cycle is well reproduced, with the median amplitude of the models' seasonal standard deviations being only 2.4% larger than observed. Half the seasonal amplitudes lie within 15% of the observed, and the median correlation found between the observed and model seasonal cycles is 0.95. The dominant seasonal error is an under- estimation of AAM during northern hemisphere winter associated with errors in the position of subtropical jets. Less robust are the modeled interannual variations, although the median correlation of 0.61 between model simulations and observed AAM is statistically significant. The two El Nino-Southern Oscillation events that occurred during the AMIP decade 1979-1988 have the expected positive AAM anomalies, although the AAM signature of the 1982-1983 event tends to be underestimated and that of the 1986-1987 event overestimated.
Hide, R.↗
High accuracy earth rotation and atmospheric angular momentum
Recent advances in the measurement and interpretation of earth rotation and polar motion are discussed with attention focusing on short period fluctuations and their relationship to changes in the global atmospheric angular momentum (AAM). Data acquired during the MERIT campaign are used. Fluctuations in the earth's rotation over a time scale of a year or less are dominated by atmospheric effects; agreement is found between changes in length of day and AAM estimates.
Dickey, J. O.↗
The Madden-Julian oscillation and the angular momentum balance in a barotropic ocean model
The oceanic response to the Madden and Julian (1971, 1972) oscillation (MJO) wind stresses are studied with special attention given to the nature of the related angular momentum exchanges between the ocean and the solid earth for idealized 40- and 50-day fluctuations of Pacific winds. The character of these exchanges is illustrated with the use of numerical solutions of a shallow water ocean model, which were found for a constant depth basin centered on the equator and extending over 140 deg in longitude. Solutions also suggest that even small (0.5-1.5-cm) coastal sea level fluctuations can cause variations in the length of day comparable to observed values in the 40- to 50-day band.
Ponte, Rui M.↗
Approaches to Power Spectrum Estimation of Atmospheric Angular Momentum
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atmospheric angular momentum (AAM) El Nino-Souther↗
An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers
The high-resolution laboratory millimeter- and submillimeter-wave spectra of C-12H(3)OH and C-13H(3)OH have been extended to include transitions involving significantly higher angular momentum quantum numbers than studied previously. For C-12H(3)OH, the data set now includes 549 A torsional substate transitions and 524 E torsional substate transitions through J is not greater than 24, exclusive of blends. For C-13H(3)OH the data set now includes 453 A torsional substate transitions and 440 E torsional substate transitions through J is not greater than 24, exclusive of blends. The extended internal axis method Hamiltonian has been used to analyze the transitions to experimental accuracy. The molecular constants determined by this approach have been used to predict accurately the frequencies of many transitions through J = 25 not measured in the laboratory.
Anderson, Todd↗
Effect of orbital and rotational angular momentum averaging on branching ratios of dynamical resonances in the reaction H + p-H2 yields o-H2 + H
The paper reports extensive quantum mechanical calculations of the product vibrational branching ratios in the reaction H + p-H2 yields o-H2 + H. The calculations involve total angular momentum up to 2 and excited as well as ground initial rotational states, and they are completely converged with up to 513 channels in individual total angular momentum/parity blocks. Comparisons are made with recent experiments by Nieh and Valentini.
Mladenovic, Mirjana↗