Engineering topics

Quirk, W. J.

Publications and source records attributed to Quirk, W. J..

14 records

NASA NTRS1978

The GISS sounding temperature impact test

The impact of DST 5 and DST 6 satellite sounding data on mid-range forecasting was studied. The GISS temperature sounding technique, the GISS time-continuous four-dimensional assimilation procedure based on optimal statistical analysis, the GISS forecast model, and the verification techniques developed, including impact on local precipitation forecasts are described. It is found that the impact of sounding data was substantial and beneficial for the winter test period, Jan. 29 - Feb. 21. 1976. Forecasts started from initial state obtained with the aid of satellite data showed a mean improvement of about 4 points in the 48 and 772 hours Sub 1 scores as verified over North America and Europe. This corresponds to an 8 to 12 hour forecast improvement in the forecast range at 48 hours. An automated local precipitation forecast model applied to 128 cities in the United States showed on an average 15% improvement when satellite data was used for numerical forecasts. The improvement was 75% in the midwest.

Halem, M.↗

NASA NTRS1978

An initial state perturbation experiment with the GISS model

Monthly mean global forecasts for January 1975 have been computed with the Goddard Institute for Space Studies model from four slightly different sets of initial conditions - a 'control' state and three random perturbations thereof - to simulate the effects of initial state uncertainty on forecast quality. Differences among the forecasts are examined in terms of energetics, synoptic patterns and forecast statistics. The 'noise level' of the model predictions is depicted on global maps of standard deviations of sea level pressures, 500 mb heights and 850 mb temperatures for the set of four forecasts. Initial small-scale random errors do not appear to result in any major degradation of the large-scale monthly mean forecast beyond that generated by the model itself, nor do they appear to represent the major source of large-scale forecast error.

Spar, J.↗

NASA NTRS1977

A comparative study of the effects of albedo change on drought in semi-arid regions

Numerical simulation studies of the effects of changes in albedo on rainfall involve comparisons of semiarid areas, lying at the boundary between a major desert and an adjacent monsoonal region, with areas of the same size located within the monsoonal region itself. The sensitivity of the rainfall to the ground hydrology was determined by performing the albedo simulations with two different evapotranspiration parameterizations, one giving too high evaporation over land and the other giving negligible evaporation over land. The evaporation rate is, in general, found to have as important an effect as changes in albedo. The mechanism by which an increase of albedo reduces the rainfall during conditions of high evaporation is considered.

Charney, J.↗

NASA NTRS1977

Recent improvements in the GISS model of the global atmosphere

A simulation of the July climatology by the GISS GCM produced tropospheric temperatures which were systematically 1-2 C lower than the observed temperatures in the middle latitudes of the Northern Hemisphere. Convective cloud cover was nearly double the observed level in this region. Planetary albedo was much higher than the observed July value and showed the wrong seasonal trend. These problems have been solved through modifications of the GISS scheme for the parameterization of cumulus convection.

Helfand, H. M.↗

NASA NTRS1977

The effect of increased horizontal resolution on synoptic forecasts with the GISS model of the global atmosphere

The improved horizontal resolution global circulation model in question has a horizontal spacing of 2.5 deg latitude by 3 deg longitude for a resolution of about 250 km in midlatitude. This paper reports on experiments to determine the improvements in forecasting skill and in initial conditions that were made possible by the ultrafine resolution and ultrafine assimilation. The size of the improvement in skill score when the ultrafine model is used for forecasting and assimilation was so large that 60-hour forecasts with the ultrafine model had as good a skill score as the 48-hour forecasts with the fine model. Synoptic evaluations confirmed that ultrafine model forecasts are better than the fine model forecasts.

Quirk, W. J.↗

NASA NTRS1976

A search for short-term meteorological effects of solar variability in an atmospheric circulation model

A set of numerical experiments is carried out to test the short-range sensitivity of the Goddard Institute for Space Studies global atmospheric general-circulation model to changes in solar constant and ozone amount. These experiments consist of forecasts initiated with actual atmospheric data. One set of forecasts is made with a standard version of the model; another set uses the model modified by very different values of the solar constant (two-thirds and three-halves of the standard value) and of the ozone amount (zero and twice the standard amount). Twelve-day integrations with these very large variations show such small effects that the effects of realistic variations would almost certainly be insignificant meteorologically on this time scale.

Somerville, R. C. J.↗

NASA NTRS1975

Drought in the Sahara - A biogeophysical feedback mechanism

Two integrations of a global general circulation model, differing only in the prescribed surface albedo in the Sahara, show that an increase in albedo resulting from a decrease in plant cover causes a decrease in rainfall. Thus any tendency for plant cover to decrease would be reinforced by a decrease in rainfall, and could initiate or perpetuate a drought.

Charney, J.↗

NASA NTRS1975

Numerical experiments on short-term meteorological effects on solar variability

A set of numerical experiments was conducted to test the short-range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day sets of integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Any causal relationships between solar variability and weather, for time scales of two weeks or less, rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

Somerville, R. C. J.↗

NASA NTRS1975

Seasonal changes in the atmospheric heat balance simulated by the GISS general circulation model

Tests of the ability of numerical general circulation models to simulate the atmosphere have focussed so far on simulations of the January climatology. These models generally present boundary conditions such as sea surface temperature, but this does not prevent testing their ability to simulate seasonal changes in atmospheric processes that accompany presented seasonal changes in boundary conditions. Experiments to simulate changes in the zonally averaged heat balance are discussed since many simplified models of climatic processes are based solely on this balance.

Stone, P. H.↗

NASA NTRS1974

The effect of small-scale vertical mixing of horizontal momentum in a general circulation model

Several experiments are described in which the sub-grid-scale vertical eddy viscosity in the GISS global general circulation model was varied. The results show that large viscosities suppress large-scale eddies in middle and high latitudes, but enhance the circulation in the tropical Hadley cell and increase the extent of the tropical easterlies. Comparison with observations shows that the GISS model requires eddy viscosities about 1 sq m per sec or less to give realistic results for middle and high latitudes, and eddy viscosities about 100 sq m per sec to give realistic results for low latitudes. A plausible mechanism for the implied increase in small-scale mixing in low latitudes is cumulus convection.

Stone, P. H.↗

NASA NTRS1974

Numerical experiments on short-term meteorological effects of solar variability

Set of numerical experiments has been carried out to test the short range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Thus any causal relationships between solar variability and weather, for time scales of two weeks or less, will have to rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

Somerville, R. C. J.↗

NASA NTRS1974

The GISS model of the global atmosphere

A description and numerical results are presented for a global atmospheric circulation model developed at the Goddard Institute for Space Studies (GISS). The model version described is a 9-level primitive-equation model in sigma coordinates. It includes a realistic distribution of continents, oceans and topography. Detailed calculations of energy transfer by solar and terrestrial radiation make use of cloud and water vapor fields calculated by the model. The model hydrologic cycle includes two precipitation mechanisms: large-scale supersaturation and a parameterization of subgrid-scale cumulus convection. Results are presented both from a comparison of the 13th to the 43rd days (January) of one integration with climatological statistics, and from five short-range forecasting experiments. In the extended integration, the near-equilibrium January-mean model atmosphere exhibits an energy cycle in good agreement with observational estimates, together with generally realistic zonal mean fields of winds, temperature, humidity, transports, diabatic heating, evaporation, precipitation, and cloud cover.

Somerville, R. C. J.↗

NASA NTRS1973

Do interstellar gas clouds exist between spiral arms.

This paper discusses what can happen to clouds as they move from arm regions to interarm regions, through a density-wave shock, and back to arm regions again. Shu et al. (1972) have taken the viewpoint that interstellar clouds will survive the trip between arms. Biermann et al. (1972) have taken the viewpoint that they will not. We shall point out that cloud-cloud collisions and other processes may lead to the destruction of interstellar clouds in less time than the 100 m.y. it takes clouds to travel across arms. A possible observational test is suggested to distinguish between the two possibilities.

Quirk, W. J.↗

NASA NTRS1973

Star formation and evolution in spiral galaxies.

Evolutionary models for regions of M31 and M33 and the solar neighborhood are based on a stellar birthrate suggested by the dynamics of spiral structure: we assume that stars are formed very efficiently until the gas content reaches equilibrium at its present value, which takes about 1 b.y.; thereafter, the birthrate just equals the rate at which gas enters the system from stellar mass-loss or infall of intergalactic matter. Each model represents an average around a cylindrical-shell-shaped region, which is homogeneous and closed except for possible infall. The disk and spiral-arm populations only are considered. Each star is followed in the H-R diagram from the main sequence to death as an invisible remnant. Integrated magnitudes, colors, mass-to-light ratio (M/L), gas content, helium and metal abundance (Z), are computed in steps of 1 b.y.

Quirk, W. J.↗