Engineering topics

Stone, Peter H.

Publications and source records attributed to Stone, Peter H..

12 records

NASA NTRS2005

Research on the Natural Variability of Climate and the Impact of Anthropogenic Forcing on Climate

The paper, "Latitude-dependent vertical mixing and the tropical thermocline in a global OGCM", was revised and published in Geophysical Research Letters. It treats the new GISS mixing scheme which includes the latitudinal dependence of the interior ocean turbulence field reported by Gregg, Sanford & Winkel. When implemented in the 3x3 degree NCAR CSMl OGCM [NCOMl] the new mixing scheme produces an improved, sharper equatorial thermoclines in both the Atlantic and the Pacific while simultaneously maintaining the realistic meridional overturning and northward heat transports found already with the previous GISS scheme. Also the paper "Diagnostics of the oceanic thermohaline circulation in a coupled climate model" describing earlier work on the grany was published.

Stone, Peter H.↗

NASA NTRS2000

Participation in the GISS EOS Proposal

To model the mass balance of the Greenland and Antarctic ice-sheets, Research Assistant Veronique Bugnion developed a snowpack model which embodies a physically based approach to modeling the temperature and density distribution of a snow, firn, and ice mixture. The snowpack model performed satisfactorily in capturing the surface energy balance and melt amounts measured at stations in Greenland and Antarctica. Also a comparison between the predicted extent of the wet snow zone obtained with the model and the same quantity derived from satellite microwave measurements showed excellent agreement. In addition the model's simulated total runoff was close to the best estimates from observations for the Greenland and Antarctic ice caps. Ms. Bugnion and research scientist Andrei Sokolov coupled the snowpack model to the climate submodel of MIT's Integrated Global System Model (IGSM) and integrated forward over the 21st century for a range of climate change scenarios, using forcings from simulations with the IGSM. The changes in mass balance of the ice caps were then translated into changes in sea level. For the scenarios with small to moderate warming, the runoff from Greenland and Antarctica is minimal. For the scenarios with a larger warming, there is a net increase in sea-level of 2-3 cm from Greenland, and a decrease of between 2 and 5 cm from Antarctica. These results show that the net change in sea level which can be expected to follow climatic changes in the Arctic and Antarctic regions, a decrease of 2 to 4 cm or less by the end of the 21st century, is smaller than most previously published estimates.

Stone, Peter H.↗

NASA NTRS1994

Radiative-convective model with an explicit hydrologic cycle. 2: Sensitivity to large changes in solar forcing

The one-dimensional radiative-convective equilibrium model with an explicit hydrologic cycle introduced in part 1 is used to study the sensitivity of the model's atmosphere to large changes in the solar forcing, when various cumulus convection parameterizations are used. When the concentration of the absorbing as in the atmosphere is temperature dependent, equilibrium is impossible for values of the solar forcing larger than a critical value. This result is referred to as a runaway greenhouse. The cumulus convection parameterization schemes currently in use in global climate models (GCMs) employ different assumptions about moistening. This causes the critical solar forcing above which a runaway greenhouse occurs to be very sensitive to the cumulus convection scheme employed. Furthermore, we show that the sensitivity of the equilibrium temperature to changes in the solar forcing depends crucially on the microphysics of cumulus convection. For fixed cloud conditions, the critical forcing for a runaway greenhouse to occur is between approximately 1.22 and 1.49 times the global mean value for the Earth, and for clear sky conditions, it is a few percent lower. The runaway greenhouse in the experiments with the mass flux schemes generally occurs more rapidly than in the experiments with the adjustment schemes. In addition, the inability of the hard convective adjustment scheme to produce an efficient vertical transport of moisture, together with the saturation requirement for convection to occur, leads to the breakdown of the radiative-convective equilibria when other processes are not available to provide the necessary vertical transport of water vapor.

Renno, Nilton O.↗

NASA NTRS1994

Numerical analysis and modeling of atmospheric phenomena

For the past 22 years Grant NGR 22-009-727 has been supporting research in the Center for Meteorology and Physical Oceanography (and its predecessors) in a wide variety of diagnostic and modeling studies of atmospheric and ocean phenomena. Professor Jule Charney was the initial Principal Investigator. Professor Peter Stone joined him as co-Principal Investigator in 1975 and became the sole Principal Investigator in 1981. During its lifetime the Grant has supported in whole or in part 11 Master's theses, 14 Ph.D. theses, and 45 papers published in refereed scientific journals. All of these theses and papers (with bibliographic references) are listed below. All but one of the theses were used to fulfill the requirements for MIT (Massachusetts Institute of Technology) degrees and are available from the MIT libraries. The one exception is F. Chen's Ph.D. thesis which was for a Harvard degree and is available from the Harvard libraries. In addition to the work described in the citations listed below, the Grant has supported Research Assistant Amy Solomon during the past two years to carry out a study of how baroclinic adjustment is affected by vertical resolution, vertical temperature structure, and dissipation. Ms. Solomon plans to use this project for her Ph.D. thesis. Support for this project will continue under NASA Grant NAG 5-2490, 'The Factors Controlling Poleward Heat Transport in Climate Models.'

Stone, Peter H.↗

NASA NTRS1993

The role of large-scale eddies in the climate equilibrium. Part 2: Variable static stability

Lorenz's two-level model on a sphere is used to investigate how the results of Part 1 are modified when the interaction of the vertical eddy heat flux and static stability is included. In general, the climate state does not depend very much on whether or not this interaction is included, because the poleward eddy heat transport dominates the eddy forcing of mean temperature and wind fields. However, the climatic sensitivity is significantly affected. Compared to two-level model results with fixed static stability, the poleward eddy heat flux is less sensitive to the meridional temperature gradient and the gradient is more sensitive to the forcing. For example, the logarithmic derivative of the eddy flux with respect to the gradient has a slope that is reduced from approximately 15 on a beta-plane with fixed static stability and approximately 6 on a sphere with fixed static stability, to approximately 3 to 4 in the present model. This last result is more in line with analyses from observations. The present model also has a stronger baroclinic adjustment than that in Part 1, more like that in two-level beta-plane models with fixed static stability, that is, the midlatitude isentropic slope is very insensitive to the forcing, the diabatic heating, and the friction, unless the forcing is very weak.

Zhou, Shuntai↗

NASA NTRS1993

The role of large-scale eddies in the climate equilibrium. I - Fixed static stability

An efficient two-level model on a sphere that is based on the balance equations with fixed static stability is developed and used to study how eddies arising from baroclinic instability interact with the temperature structure. The model gives a much better simulation of the eddy momentum flux and of the total eddy forcing of the zonal-mean temperature and zonal wind fields than do quasi-geostrophic beta-plane models. Nonetheless, the results are qualitatively similar. The midlatitude eddy regimes range between two extreme cases. In one, the eddies have no effect on the temperature and zonal wind fields, and in the other (similar to the observed atmosphere), the eddy forcing of the temperature and zonal wind fields is dominated by the eddy heat flux. Quantitatively, some of the model's results differ significantly from those based on the quasi-geostrophic beta-plane. For example, the temperature structure is much more sensitive to the external forcing, and the eddy heat flux is less sensitive to the temperature structure.

Zhou, Shuntai↗

NASA NTRS1991

Vertical eddy heat fluxes from model simulations

Vertical eddy fluxes of heat are calculated from simulations with a variety of climate models, ranging from three-dimensional GCMs to a one-dimensional radiative-convective model. The models' total eddy flux in the lower troposphere is found to agree well with Hantel's analysis from observations, but in the mid and upper troposphere the models' values are systematically 30 percent to 50 percent smaller than Hantel's. The models nevertheless give very good results for the global temperature profile, and the reason for the discrepancy is unclear. The model results show that the manner in which the vertical eddy flux is carried is very sensitive to the parameterization of moist convection. When a moist adiabatic adjustment scheme with a critical value for the relative humidity of 100 percent is used, the vertical transports by large-scale eddies and small-scale convection on a global basis are equal: but when a penetrative convection scheme is used, the large-scale flux on a global basis is only about one-fifth to one-fourth the small-scale flux. Comparison of the model results with observations indicates that the results with the latter scheme are more realistic. However, even in this case, in mid and high latitudes the large and small-scale vertical eddy fluxes of heat are comparable in magnitude above the planetary boundary layer.

Stone, Peter H.↗

NASA NTRS1990

On the limitations of General Circulation Climate Models

General Circulation Models (GCMs) by definition calculate large-scale dynamical and thermodynamical processes and their associated feedbacks from first principles. This aspect of GCMs is widely believed to give them an advantage in simulating global scale climate changes as compared to simpler models which do not calculate the large-scale processes from first principles. However, it is pointed out that the meridional transports of heat simulated GCMs used in climate change experiments differ from observational analyses and from other GCMs by as much as a factor of two. It is also demonstrated that GCM simulations of the large scale transports of heat are sensitive to the (uncertain) subgrid scale parameterizations. This leads to the question whether current GCMs are in fact superior to simpler models for simulating temperature changes associated with global scale climate change.

Stone, Peter H.↗

NASA NTRS1990

Development of a two-dimensional zonally averaged statistical-dynamical model. III - The parameterization of the eddy fluxes of heat and moisture

A number of perpetual January simulations are carried out with a two-dimensional zonally averaged model employing various parameterizations of the eddy fluxes of heat (potential temperature) and moisture. The parameterizations are evaluated by comparing these results with the eddy fluxes calculated in a parallel simulation using a three-dimensional general circulation model with zonally symmetric forcing. The three-dimensional model's performance in turn is evaluated by comparing its results using realistic (nonsymmetric) boundary conditions with observations. Branscome's parameterization of the meridional eddy flux of heat and Leovy's parameterization of the meridional eddy flux of moisture simulate the seasonal and latitudinal variations of these fluxes reasonably well, while somewhat underestimating their magnitudes. New parameterizations of the vertical eddy fluxes are developed that take into account the enhancement of the eddy mixing slope in a growing baroclinic wave due to condensation, and also the effect of eddy fluctuations in relative humidity. The new parameterizations, when tested in the two-dimensional model, simulate the seasonal, latitudinal, and vertical variations of the vertical eddy fluxes quite well, when compared with the three-dimensional model, and only underestimate the magnitude of the fluxes by 10 to 20 percent.

Stone, Peter H.↗

NASA NTRS1988

Observations of the 30-60 day oscillation in zonal mean atmospheric angular momentum and high cloud cover

Zonally averaged momentum and high-cloud data were analyzed for the periods of April-October 1979 and November 1982-October 1983 periods. The analysis yielded belt correlation fields implying a symmetry and propagation of momentum out of the tropics in the momentum data and an asymmetrical oscillation across the equatorial zone in the high-cloud data. The 30-60 day oscillation was found to be the dominant periodicity in tropical and subtropical belts in both the momentum and cloud fields, with variation of time spectra evident between 1979 and 1983. The lag correlations between high cloud belts and momentum belts showed strong correlations with the 30-60 day oscillation present. Anomalously high/low zonal mean high cloudiness in the tropics was accompanied by anomalously high/low zonal mean momentum in the tropics, with the latter anomalies subsequently propagating into midlatitudes.

Risbey, James S.↗

NASA NTRS1987

Development of a two-dimensional zonally averaged statistical-dynamical model. II - The role of eddy momentum fluxes in the general circulation and their parameterization

The role of eddy momentum fluxes in the general circulation was investigated using a two-dimensional zonally averaged statistical-dynamical model described by Yao and Stone (1987), which is almost two orders of magnitude faster than the three-dimensional climate model of Hansen et al. (1983). Results show that the vertical structure of the meridional eddy flux has relatively little impact on the general circulation, presumably because the vertical structure is strongly constrained by the thermal wind relation and surface friction. On the other hand, it was found that, in order to simulate accurately the general circulation and its response to climate changes, parameterization of the vertically integrated meridional eddy flux of angular momentum is necessary. A new parameterization of this eddy momentum transport was carried out, which is intended to represent the transport due to large-scale transient eddies arising from baroclinic instability.

Stone, Peter H.↗

NASA NTRS1987

Development of a two-dimensional zonally averaged statistical-dynamical model. I - The parameterization of moist convection and its role in the general circulation

The moist convection parameterization used in the GISS 3-D GCM is adapted for use in a two-dimensional (2-D) zonally averaged statistical-dynamical model. Experiments with different versions of the parameterization show that its impact on the general circulation in the 2-D model does not parallel its impact in the 3-D model unless the effect of zonal variations is parameterized in the moist convection calculations. A parameterization of the variations in moist static energy is introduced in which the temperature variations are calculated from baroclinic stability theory, and the relative humidity is assumed to be constant. Inclusion of the zonal variations of moist static energy in the 2-D moist convection parameterization allows just a fraction of a latitude circle to be unstable and enhances the amount of deep convection. This leads to a 2-D simulation of the general circulation very similar to that in the 3-D model. The experiments show that the general circulation is sensitive to the parameterized amount of deep convection in the subsident branch of the Hadley cell. The more there is, the weaker are the Hadley cell circulations and the westerly jets. The experiments also confirm the effects of momentum mixing associated with moist convection found by earlier investigators and, in addition, show that the momentum mixing weakens the Ferrel cell. An experiment in which the moist convection was removed while the hydrological cycle was retained and the eddy forcing was held fixed shows that moist convection by itself stabilizes the tropics, reduces the Hadley circulation, and reduces the maximum speeds in the westerly jets.

Yao, Mao-Sung↗