scholarly journals Solar 5-min Oscillation Amplitude Anisotropy and Doppler Velocity Systematics

1988 ◽  
Vol 123 ◽  
pp. 63-65
Author(s):  
J.R. Kuhn ◽  
C.M. O'Neill ◽  
L.B. Gilliam
Keyword(s):  
Spatial Resolution ◽  
Oscillation Amplitude ◽  
Level Line ◽  
Line Center ◽  
Doppler Velocity ◽  
Systematic Effect ◽  
Conflicting Information ◽  
Doppler Shifts ◽  
Line Asymmetry ◽  
Observing Techniques

Several measurements of 5-min velocity amplitudes have yielded confusing and conflicting information on the l and m dependence of the modal excitation (Kuhn and O'hanlon, 1983 – henceforth KO; Deubner, 1985; and Hill et al. 1985). We have obtained considerably more data than was described in KO using similar observing techniques. Additional analysis has illuminated a systematic effect related to the finite spatial resolution, and line asymmetry of the data that can lead to errors in inferred velocity amplitudes. Even though Doppler shifts are calculated from the Fraunhofer line center positions the effect can lead to 5-min oscillation amplitude errors at the 10 percent or greater level. Line wing observations should be more susceptible, and comparable resolution 2-dimensional data may be less sensitive to this systematic.

scholarly journals Doppler shift oscillations of a sunspot detected by CYRA and IRIS

2020 ◽  
Vol 642 ◽  
pp. A231
Author(s):  
D. Li ◽  
X. Yang ◽  
X. Y. Bai ◽  
J. T. Su ◽  
Z. J. Ning ◽  
...  
Keyword(s):  
Line Profile ◽  
Gaussian Function ◽  
Correlation Method ◽  
Doppler Velocity ◽  
Temperature Minimum ◽  
Sunspot Umbra ◽  
Spatially Resolved ◽  
Doppler Shifts ◽  
Time Distance ◽  
The Moment

Context. The carbon monoxide (CO) molecular line at around 46655 Å in solar infrared spectra is often used to investigate the dynamic behavior of the cold heart of the solar atmosphere, i.e., sunspot oscillation, especially at the sunspot umbra. Aims. We investigated sunspot oscillation at Doppler velocities of the CO 7-6 R67 and 3-2 R14 lines that were measured by the Cryogenic Infrared Spectrograph (CYRA), as well as the line profile of Mg II k line that was detected by the Interface Region Imaging Spectrograph (IRIS). Methods. A single Gaussian function is applied to each CO line profile to extract the line shift, while the moment analysis method is used for the Mg II k line. Then the sunspot oscillation can be found in the time–distance image of Doppler velocities, and the quasi-periodicity at the sunspot umbra are determined from the wavelet power spectrum. Finally, the cross-correlation method is used to analyze the phase relation between different atmospheric levels. Results. At the sunspot umbra, a periodicity of roughly 5 min is detected at the Doppler velocity range of the CO 7-6 R67 line that formed in the photosphere, while a periodicity of around 3 min is discovered at the Doppler velocities of CO 3-2 R14 and Mg II k lines that formed in the upper photosphere or the temperature minimum region and the chromosphere. A time delay of about 2 min is measured between the strong CO 3-2 R14 line and the Mg II k line. Conclusions. Based on the spectroscopic observations from the CYRA and IRIS, the 3 min sunspot oscillation can be spatially resolved in the Doppler shifts. It may come from the upper photosphere or the temperature minimum region and then propagate to the chromosphere, which might be regarded as a propagating slow magnetoacoustic wave.

scholarly journals Infrared Doppler Oscillations in a Solar Filament

1998 ◽  
Vol 167 ◽  
pp. 139-142 ◽  
Author(s):  
R. Molowny-Horas ◽  
R. Oliver ◽  
J.L. Ballester ◽  
F. Baudin
Keyword(s):  
Wavelet Analysis ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Power Spectra ◽  
Doppler Shifts ◽  
Solar Filament ◽  
Periodic Signals

AbstractWe present the results of a high spatial resolution investigation of Doppler oscillations in a solar filament, using the He I 10830Å infrared line. Fourier power spectra of Doppler shifts reveal the presence of periodic signals. Two features, showing oscillations at 2.7 min and 12.5 min, have been studied. The use of the so-called wavelet analysis enables us to estimate the size of both features at 2.7 arc sec and 4.75 arc sec, respectively. Their approximate lifetimes are 10 min and 20 min.

scholarly journals Rapid Variations in Intergranular Space

1993 ◽  
Vol 141 ◽  
pp. 222-224 ◽  
Author(s):  
A. Nesis ◽  
A. Hanslmeier ◽  
R. Hammer ◽  
R. Komm ◽  
W. Mattig ◽  
...  
Keyword(s):  
Line Width ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Doppler Velocity ◽  
Continuum Intensity ◽  
Velocity Gradients ◽  
The Continuum ◽  
Intergranular Space

AbstractSpectrograms of high spatial resolution taken every 15s reveal rapid variations of the continuum intensity and line width. Variations of the latter seem to be related to Doppler velocity gradients.

scholarly journals The next generation airborne polarimetric Doppler weather radar

2014 ◽  
Vol 3 (2) ◽  
pp. 111-126 ◽  
Author(s):  
J. Vivekanandan ◽  
W.-C. Lee ◽  
E. Loew ◽  
J. L. Salazar ◽  
V. Grubišić ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Phased Array ◽  
Doppler Velocity ◽  
Airborne Radar ◽  
Dual Polarization ◽  
Polarization Measurements ◽  
Phased Array Radar ◽  
X Band ◽  
Temporal And Spatial ◽  
Airborne Phased Array Radar

Abstract. Results from airborne field deployments emphasized the need to obtain concurrently high temporal and spatial resolution measurements of 3-D winds and microphysics. A phased array radar on an airborne platform using dual-polarization antenna has the potential for retrieving high-resolution, collocated 3-D winds and microphysical measurements. Recently, ground-based phased array radar (PAR) has demonstrated the high time-resolution estimation of accurate Doppler velocity and reflectivity of precipitation and clouds when compared to mechanically scanning radar. PAR uses the electronic scanning (e-scan) to rapidly collect radar measurements. Since an airborne radar has a limited amount of time to collect measurements over a specified sample volume, the e-scan will significantly enhance temporal and spatial resolution of airborne radar observations. At present, airborne weather radars use mechanical scans, and they are not designed for collecting dual-polarization measurements to remotely estimate microphysics. This paper presents a possible configuration of a novel airborne phased array radar (APAR) to be installed on an aircraft for retrieving improved dynamical and microphysical scientific products. The proposed APAR would replace the aging, X-band Electra Doppler radar (ELDORA). The ELDORA X-band radar's penetration into precipitation is limited by attenuation. Since attenuation at C-band is lower than at X-band, the design specification of a C-band airborne phased array radar (APAR) and its measurement accuracies are presented. Preliminary design specifications suggest the proposed APAR will meet or exceed ELDORA's current sensitivity, spatial resolution and Doppler measurement accuracies of ELDORA and it will also acquire dual-polarization measurements.

scholarly journals The Centre-of-Mass Velocity of a Radially Pulsating Star: Insights from NLTE Models

1995 ◽  
Vol 155 ◽  
pp. 375-376
Author(s):  
Dimitar D. Sasselov
Keyword(s):  
Mass Velocity ◽  
Radiation Hydrodynamics ◽  
Systematic Effect ◽  
Centre Of Mass ◽  
Line Asymmetry

AbstractThe problem of deriving the centre-of-mass velocity of a radially pulsating star is reexamined. New observations of line asymmetry and Non-LTE radiation hydrodynamics point to a systematic effect of about 1 km s−1 in Cepheids.

scholarly journals Recent Progress in Solar or Stellar Interior Modelling

2001 ◽  
Vol 203 ◽  
pp. 29-39 ◽  
Author(s):  
S. Turck-Chièze
Keyword(s):  
Spatial Resolution ◽  
Sound Speed ◽  
Reaction Rates ◽  
Solar Interior ◽  
Stellar Structure ◽  
Dynamical Instability ◽  
Integration Time ◽  
Doppler Velocity ◽  
Velocity Measurements ◽  
Acoustic Modes

Acoustic modes are well-suited probes to check the internal stellar structure and bring interesting constraints on turbulence regions, mixing in stellar interiors and magnetic fields. The SOHO satellite, through the helioseismic instruments GOLF, MDI and VIRGO, has significantly improved the knowledge of these modes owing to an excellent duty cycle (greater than 90%) and the capability to detect very low amplitude modes, down to 3 mm/s. Five years of the SOHO misson guarantee an accurate view of the solar interior, weakly dependent on the turbulent surface, from the energy-generating core to the surface.The recent results allow us to verify some of the theoretical assumptions of stellar modelling. The tachocline layers, located in a narrow region at the base of the convection zone, support an hydro (or magnetohydro) dynamical instability which induces mixing and results in 7Li depletion in accordance with photospheric observations. On the contrary, central mixing is not favoured by the present observations. Nuclear reaction rates of the pp chain are now constrained by the behaviour of the sound speed and density. Döppler velocity measurements appear as an excellent technique to follow in real time the temporal evolution of the luminosity produced in the core. Some puzzling questions about dynamical effects in stellar plasmas can now start to be addressed for the first time. The theoretical neutrino emissions can be now directly deduced from our helioseismic vision of the energy-generating core.Nowadays, helioseismology provides a dynamical vision of the external half of the Sun (20% in mass), as a result of the extraction of the sound speed, density, rotation profiles and of the time evolution of velocity measurements. Below, the classical static vision of the nuclear region persists because of the poor spatial resolution offered by acoustic modes (±6% in radius, 10% in mass) and the long integration time (several years). Gravity modes will be extremely useful to improve the spatial resolution in the radiative region. The extended observations with the SOHO satellite may be extremely useful to detect some of these modes.

scholarly journals The EISCAT meteor code

2008 ◽  
Vol 26 (8) ◽  
pp. 2303-2309 ◽  
Author(s):  
G. Wannberg ◽  
A. Westman ◽  
J. Kero ◽  
C. Szasz ◽  
A. Pellinen-Wannberg
Keyword(s):  
Matched Filter ◽  
Binary Sequence ◽  
Time Of Flight ◽  
Target Range ◽  
Doppler Velocity ◽  
Range Resolution ◽  
Doppler Shifts ◽  
Low Sidelobe ◽  
Short Time ◽  
Receiver Bandwidth

Abstract. The EISCAT UHF system has the unique capability to determine meteor vector velocities from the head echo Doppler shifts measured at the three sites. Since even meteors spending a very short time in the common volume produce analysable events, the technique lends itself ideally to mapping the orbits of meteors arriving from arbitrary directions over most of the upper hemisphere. A radar mode optimised for this application was developed in 2001/2002. A specially selected low-sidelobe 32-bit pseudo-random binary sequence is used to binary phase shift key (BPSK) the transmitted carrier. The baud-length is 2.4 μs and the receiver bandwidth is 1.6 MHz to accommodate both the resulting modulation bandwidth and the target Doppler shift. Sampling is at 0.6 μs, corresponding to 90-m range resolution. Target range and Doppler velocity are extracted from the raw data in a multi-step matched-filter procedure. For strong (SNR>5) events the Doppler velocity standard deviation is 100–150 m/s. The effective range resolution is about 30 m, allowing very accurate time-of-flight velocity estimates. On average, Doppler and time-of-flight (TOF) velocities agree to within about one part in 103. Two or more targets simultaneously present in the beam can be resolved down to a range separation <300 m as long as their Doppler shifts differ by more than a few km/s.

Observations of the Boundary Layer near Tornadoes and in Supercells Using a Mobile, Collocated, Pulsed Doppler Lidar and Radar

2014 ◽  
Vol 31 (2) ◽  
pp. 302-325 ◽  
Author(s):  
Howard B. Bluestein ◽  
Jana B. Houser ◽  
Michael M. French ◽  
Jeffrey C. Snyder ◽  
George D. Emmitt ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Spatial Resolution ◽  
Phased Array ◽  
High Spatial Resolution ◽  
Vertical Shear ◽  
Doppler Velocity ◽  
Doppler Lidar ◽  
Pulsed Doppler ◽  
Ground Clutter ◽  
X Band

Abstract During the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2), in the spring of 2010, a mobile and pulsed Doppler lidar system [the Truck-Mounted Wind Observing Lidar Facility (TWOLF)] mounted on a truck along with a mobile, phased-array, X-band Doppler radar system [Mobile Weather Radar–2005 X-band, phased array (MWR-05XP)] was used to complement Doppler velocity coverage in clear air near the radar–lidar facility and to provide high-spatial-resolution vertical cross sections of the Doppler wind field in the clear-air boundary layer near and in supercells. It is thought that the magnitude and direction of vertical shear and possibly the orientation and spacing of rolls in the boundary layer have significant effects on both supercell and tornado behavior; MWR-05XP and TWOLF can provide data that can be used to measure vertical shear and detect rolls. However, there are very few detailed, time-dependent and spatially varying observations throughout the depth of the boundary layer of supercells and tornadoes. This paper discusses lidar and radar data collected in or near six supercells. Features seen by the lidar included gust fronts, horizontal convective rolls, and small-scale vortices. The lidar proved useful at detecting high-spatial-resolution, clear-air returns at close range, where the radar was incapable of doing so, thus providing a more complete picture of the boundary layer environment ahead of supercells. The lidar was especially useful in areas where there was ground-clutter contamination. When there was precipitation and probably insects, and beyond the range of the lidar, where there was no ground-clutter contamination, the radar was the more useful instrument. Suggestions are made for improving the system and its use in studying the tornado boundary layer.

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