scholarly journals Estimates of electromagnetic and turbulent energy dissipation rates under the existence of strong wind shears in the polar lower thermosphere from the European Incoherent Scatter (EISCAT) Svalbard radar observations

2004 ◽  
Vol 109 (A7) ◽  
Author(s):  
Hitoshi Fujiwara
Keyword(s):  
Energy Dissipation ◽  
Lower Thermosphere ◽  
Turbulent Energy ◽  
Strong Wind ◽  
Radar Observations ◽  
Incoherent Scatter ◽  
Dissipation Rates ◽  
Wind Shears

scholarly journals Case study of wave breaking with high-resolution turbulence measurements with LITOS and WRF simulations

2017 ◽  
Vol 17 (12) ◽  
pp. 7941-7954 ◽  
Author(s):  
Andreas Schneider ◽  
Johannes Wagner ◽  
Jens Söder ◽  
Michael Gerding ◽  
Franz-Josef Lübken
Keyword(s):  
Energy Dissipation ◽  
Wrf Model ◽  
Turbulent Energy ◽  
Weather Research And Forecasting ◽  
Strong Wind ◽  
Dissipation Rates ◽  
Stable Conditions ◽  
Wave Patterns ◽  
Turbulence Data ◽  
Vertical Winds

Abstract. Measurements of turbulent energy dissipation rates obtained from wind fluctuations observed with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) are combined with simulations with the Weather Research and Forecasting (WRF) model to study the breakdown of waves into turbulence. One flight from Kiruna (68° N, 21° E) and two flights from Kühlungsborn (54° N, 12° E) are analysed. Dissipation rates are of the order of 0. 1 mW kg−1 (∼ 0.01 K d−1) in the troposphere and in the stratosphere below 15 km, increasing in distinct layers by about 2 orders of magnitude. For one flight covering the stratosphere up to ∼ 28 km, the measurement shows nearly no turbulence at all above 15 km. Another flight features a patch with highly increased dissipation directly below the tropopause, collocated with strong wind shear and wave filtering conditions. In general, small or even negative Richardson numbers are affirmed to be a sufficient condition for increased dissipation. Conversely, significant turbulence has also been observed in the lower stratosphere under stable conditions. Observed energy dissipation rates are related to wave patterns visible in the modelled vertical winds. In particular, the drop in turbulent fraction at 15 km mentioned above coincides with a drop in amplitude in the wave patterns visible in the WRF. This indicates wave saturation being visible in the LITOS turbulence data.

scholarly journals Seasonal variability and descent of mid-latitude sporadic E layers at Arecibo

2009 ◽  
Vol 27 (3) ◽  
pp. 923-931 ◽  
Author(s):  
N. Christakis ◽  
C. Haldoupis ◽  
Q. Zhou ◽  
C. Meek
Keyword(s):  
Lower Thermosphere ◽  
Time Base ◽  
Large Set ◽  
Seasonal Behavior ◽  
Incoherent Scatter ◽  
Electron Density Gradient ◽  
Sporadic E Layers ◽  
Sporadic E Layer ◽  
Sporadic E ◽  
Wind Shears

Abstract. Sporadic E layers (Es) follow regular daily patterns in variability and altitude descent, which are determined primarily by the vertical tidal wind shears in the lower thermosphere. In the present study a large set of sporadic E layer incoherent scatter radar (ISR) measurements are analyzed. These were made at Arecibo (Geog. Lat. ~18° N; Magnetic Dip ~50°) over many years with ISR runs lasting from several hours to several days, covering evenly all seasons. A new methodology is applied, in which both weak and strong layers are clearly traced by using the vertical electron density gradient as a function of altitude and time. Taking a time base equal to the 24-h local day, statistics were obtained on the seasonal behavior of the diurnal and semidiurnal tidal variability and altitude descent patterns of sporadic E at Arecibo. The diurnal tide, most likely the S(1,1) tide with a vertical wavelength around 25 km, controls fully the formation and descent of the metallic Es layers at low altitudes below 110 km. At higher altitudes, there are two prevailing layers formed presumably by vertical wind shears associated mainly with semidiurnal tides. These include: 1) a daytime layer starting at ~130 km around midday and descending down to 105 km by local midnight, and 2) a less frequent and weaker nighttime layer which starts prior to midnight at ~130 km, descending downwards at somewhat faster rate to reach 110 km by sunrise. The diurnal and semidiurnal-like pattern prevails, with some differences, in all seasons. The differences in occurrence, strength and descending speeds between the daytime and nighttime upper layers are not well understood from the present data alone and require further study.

scholarly journals Energy Dissipation Rates of Turbulence with an Airborne Microwave Refractometer

1991 ◽  
Vol 44 (4) ◽  
pp. 435
Author(s):  
SBSS Sarma
Keyword(s):  
Refractive Index ◽  
Energy Dissipation ◽  
Vertical Gradient ◽  
Turbulence Energy ◽  
Turbulence Structure ◽  
Free Atmosphere ◽  
Dissipation Rates ◽  
Turbulence Energy Dissipation ◽  
Wind Shears ◽  
Time Basis

Estimates of turbulence energy dissipation rates have been obtained in the free atmosphere of the planetary boundary layer. These are derived in terms of the variance of radio refractive index fluctuations {Lln2 }, the Brunt-Vaisala frequency N, the mean vertical gradient of generalised potential refractive index M, and the turbulence structure parameter C~, using an airborne microwave refractometer. The energy dissipation rates thus derived are comparable with the results from other experiments. The inferred energy dissipation rates (on a near real-time basis) from the airborne microwave refractometer. are useful for detection and warning of wind shears in the atmosphere.

scholarly journals Periodicities in energy dissipation rates in the auroral mesosphere/lower thermosphere

2003 ◽  
Vol 21 (3) ◽  
pp. 787-796 ◽  
Author(s):  
C. M. Hall ◽  
S. Nozawa ◽  
C. E. Meek ◽  
A. H. Manson ◽  
Y. Luo
Keyword(s):  
Energy Dissipation ◽  
Annual Variation ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Radar Systems ◽  
Dissipation Rates ◽  
Semiannual Variation ◽  
Measuring Signal ◽  
Signal Fading ◽  
Mf Radar

Abstract. It is possible for medium-frequency (MF) radar systems to estimate kinetic energy dissipation rates by measuring signal fading times. Here, we present approximately 5 years of such results from Tromsø (69° N, 19° E) and in particular, investigate the periodicities present at different altitudes in the regime 80 to 100 km. We detect the known annual variation in the mesosphere and the semiannual variation on the lower thermosphere. In addition, other features are observed including terannual and ~ 27-day components in the lower thermosphere.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics; turbulence)

Modelling Multiphase Jet Flows for High Velocity Emulsification

2011 ◽  
Author(s):  
David Ryan ◽  
Mark Simmons ◽  
Mike Baker
Keyword(s):  
Energy Dissipation ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Jet Flows ◽  
Nozzle Orifice ◽  
Multiphase Mixture ◽  
Dissipation Rates ◽  
Mass Flow Rates ◽  
Recirculation Zones ◽  
Drop Size Distributions

Single phase steady-state Computational Fluid Dynamics (CFD) simulations are presented for turbulent flow inside a Sonolator (an industrial static mixer). Methodology is given for obtaining high quality, converged, mesh-independent results. Pressures, velocities and local specific turbulent energy dissipation rates throughout the fluid domain are obtained for three industrially-relevant mass flow rates at a fixed nozzle orifice size. Discharge coefficients calculated at the orifice are compared to literature values and to pilot plant experiments for initial validation. Streamlines in the flow are used to illustrate the presence of recirculation zones after the nozzle. Thus, residence time and peak local specific turbulent energy dissipation rates are calculated from streamline data as a function of inlet position. Values of local specific turbulent energy dissipation rate obtained are used to infer drop sizes for emulsification of a multiphase mixture under dilute, homogeneous flow conditions. The results show that different drop size distributions may be produced depending on the inlet condition of the multiphase mixture.

Sign in / Sign up

Export Citation Format

Share Document