Search NASA⌕ Search

Engineering topics

Ebel, A.

Publications and source records attributed to Ebel, A..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The QBO and weak external forcing by solar activity: A three dimensional model study

A better understanding is attempted of the physical mechanisms leading to significant correlations between oscillations in the lower and middle stratosphere and solar variability associated with the sun's rotation. A global 3-d mechanistic model of the middle atmosphere is employed to investigate the effects of minor artificially induced perturbations. The aim is to explore the physical mechanisms of the dynamical response especially of the stratosphere to weak external forcing as it may result from UV flux changes due to solar rotation. First results of numerical experiments dealing about the external forcing of the middle atmosphere by solar activity were presented elsewhere. Different numerical studies regarding the excitation and propagation of weak perturbations have been continued since then. The model calculations presented are made to investigate the influence of the quasi-biennial oscillation (QBO) on the dynamical response of the middle atmosphere to weak perturbations by employing different initial wind fields which represent the west and east phase of the QBO.

Dameris, M.↗
NASA NTRS1989

Physical mechanisms of solar activity effects in the middle atmosphere

A great variety of physical mechanisms of possibly solar induced variations in the middle atmosphere has been discussed in the literature during the last decades. The views which have been put forward are often controversial in their physical consequences. The reason may be the complexity and non-linearity of the atmospheric response to comparatively weak forcing resulting from solar activity. Therefore this review focuses on aspects which seem to indicate nonlinear processes in the development of solar induced variations. Results from observations and numerical simulations are discussed.

Ebel, A.↗
NASA NTRS1986

Horizontal wind perturbations and their relation to transient internal gravity waves

Horizontal winds as measured with the Saskatoon MF radar exhibit wind fluctuations which have preferred directions toward north or south in the period range 0 to 60 min at heights between about 60 and 110 km. Longer period perturbations (approx 1-6 h) tend to have an additional maximum of direction frequencies in the E-W sector.The polarization effect analyzed for more than 6 years shows regular changes with season. The main features of the seasonal variations of the direction distributions can be explained by directional filtering of vertically propagating nonstationary gravity waves and appropriate changes of the wave source strength and position in the troposphere. The N-S polarization of the gravity-wave field appears to result in meridional wind reversals with height above the mesopause.

Ebel, A.↗
NASA NTRS1984

Study of the system of middle atmosphere-ionosphere using remote-sensing data

In the present investigation, the methods of statistical spectral analysis are employed for a study of the quasi-periodic changes of state parameters of the middle atmosphere and the ionosphere, taking into account oscillations with periods of several days. The considered oscillations are typical for planetary waves. The theory and empirical findings regarding transient planetary waves are utilized as a basis for the concepts employed in the data analysis and for the interpretation of the results. The results of the investigation show a presence of coherent variations in the time series of radiation density measurements and other state parameters for the middle atmosphere and the ionosphere. The existence of presumably dynamic coupling processes can be recognized in oscillations with periods of about 16 or 5 days.

Hass, H.↗
NASA NTRS1976

A study of satellite observations of ozone and stratospheric temperatures during 1970-1971

A comparison is made between backscatter ultraviolet ozone data and the stratospheric radiance measurements made by the satellite infrared spectrometer on board Nimbus 4 for the period April 1970 to April 1971. These simultaneous measurements have been used to study the temporal and spatial behavior of ozone and the thermal structure of the stratosphere on a global basis. The most significant feature of the total ozone distribution observed is the strong increase in ozone values at the high latitudes of the Northern Hemisphere during the stratospheric warming of January 1971.

Ghazi, A.↗