scholarly journals Atmospheric circulation of Venus measured with visible imaging spectroscopy at the THEMIS observatory

2019 ◽  
Vol 627 ◽  
pp. A82
Author(s):  
Patrick Gaulme ◽  
François-Xavier Schmider ◽  
Thomas Widemann ◽  
Ivan Gonçalves ◽  
Arturo López Ariste ◽  
...  
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Atmospheric Circulation ◽  
Hot Spot ◽  
Imaging Spectroscopy ◽  
Rotation Period ◽  
Equatorial Region ◽  
Atmospheric Dynamics ◽  
Doppler Imaging ◽  
Meridional Winds

Measuring the atmospheric circulation of Venus at different altitudes is important for understanding its complex dynamics, in particular the mechanisms driving super-rotation. Observationally, Doppler imaging spectroscopy is in principle the most reliable way to measure wind speeds of planetary atmospheres because it directly provides the projected speed of atmospheric particles. However, high-resolution imaging spectroscopy is challenging, especially in the visible domain, and most knowledge about atmospheric dynamics has been obtained with the cloud tracking technique. The objective of the present work is to measure the global properties of the atmospheric dynamics of Venus at the altitude of the uppermost clouds, which is probed by reflected solar lines in the visible domain. Our results are based on high-resolution spectroscopic observations with the long-slit spectrometer of the solar telescope THEMIS. We present the first instantaneous “radial-velocity snapshot” of any planet of the solar system in the visible domain, i.e., a complete radial-velocity map of the planet obtained by stacking data on less than 10% of its rotation period. From this, we measured the properties of the zonal and meridional winds, which we unambiguously detect. We identify a wind circulation pattern that significantly differs from previous knowledge about Venus. The zonal wind reveals a “hot spot” structure, featuring about 200 m s−1 at sunrise and 70 m s−1 at noon in the equatorial region. Regarding meridional winds, we detect an equator-to-pole meridional flow peaking at 45 m s−1 at mid-latitudes, i.e., about twice as large as what has been reported so far.

scholarly journals Measuring planetary atmospheric dynamics with Doppler spectroscopy

2018 ◽  
Vol 617 ◽  
pp. A41 ◽  
Author(s):  
Patrick Gaulme ◽  
François-Xavier Schmider ◽  
Ivan Gonçalves
Keyword(s):  
Radial Velocity ◽  
Solar Rotation ◽  
Imaging Spectroscopy ◽  
Planetary Atmospheres ◽  
Atmospheric Dynamics ◽  
Doppler Imaging ◽  
Significant Difference ◽  
Doppler Spectroscopy ◽  
The Impact ◽  
Cloud Tracking

Doppler imaging spectroscopy is the most reliable method of directly measuring wind speeds of planetary atmospheres of the solar system. However, most knowledge about atmospheric dynamics has been obtained with cloud-tracking technique, which consists of tracking visible features from images taken at different dates. Doppler imaging is as challenging (motions can be less than 100 m s−1) as it is appealing because it measures the speed of cloud particles instead of large cloud structures. A significant difference between wind speed measured by cloud-tracking and Doppler spectroscopy is expected in case of atmospheric waves interfering with cloud structures. The purpose of this paper is to provide a theoretical basis for conducting accurate Doppler measurements of planetary atmospheres, especially from the ground with reflected solar absorption lines. We focus on three aspects which lead to significant biases. Firstly, we fully review the Young effect, which is an artificial radial velocity field caused by the solar rotation that mimics a retrograde planetary rotation. Secondly, we extensively study the impact of atmospheric seeing and show that it modifies the apparent location of the planet in the sky whenever the planet is not observed at full phase (opposition). Moreover, the seeing convolves regions of variable radial velocity and photometry, which biases radial-velocity measurements, by reducing the apparent amplitude of atmospheric motions. Finally, we propose a method to interpret the data: how to retrieve zonal, meridional, vertical, and subsolar-to-antisolar circulation from radial velocity maps, by optimizing the signal-to-noise ratio.

On the Configuration of the Magnetic Field of β CrB

1976 ◽  
Vol 32 ◽  
pp. 613-622
Author(s):  
I.A. Aslanov ◽  
Yu.S. Rustamov
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radial Velocity ◽  
Magnetic Field Strength ◽  
Complex Shape ◽  
Rotation Period ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Secular Variations ◽  
The Magnetic Field

SummaryMeasurements of the radial velocities and magnetic field strength of β CrB were carried out. It is shown that there is a variability with the rotation period different for various elements. The curve of the magnetic field variation measured from lines of 5 different elements: FeI, CrI, CrII, TiII, ScII and CaI has a complex shape specific for each element. This may be due to the presence of magnetic spots on the stellar surface. A comparison with the radial velocity curves suggests the presence of a least 4 spots of Ti and Cr coinciding with magnetic spots. A change of the magnetic field with optical depth is shown. The curve of the Heffvariation with the rotation period is given. A possibility of secular variations of the magnetic field is shown.

An Efficient Dual-Resolution Approach for Ensemble Data Assimilation and Tests with Simulated Doppler Radar Data

2008 ◽  
Vol 136 (3) ◽  
pp. 945-963 ◽  
Author(s):  
Jidong Gao ◽  
Ming Xue
Keyword(s):  
High Resolution ◽  
Data Assimilation ◽  
Radial Velocity ◽  
Computational Cost ◽  
Radar Data ◽  
Horizontal Resolution ◽  
Velocity Data ◽  
Background Error ◽  
Cross Covariance ◽  
Radial Velocity Data

Abstract A new efficient dual-resolution (DR) data assimilation algorithm is developed based on the ensemble Kalman filter (EnKF) method and tested using simulated radar radial velocity data for a supercell storm. Radar observations are assimilated on both high-resolution and lower-resolution grids using the EnKF algorithm with flow-dependent background error covariances estimated from the lower-resolution ensemble. It is shown that the flow-dependent and dynamically evolved background error covariances thus estimated are effective in producing quality analyses on the high-resolution grid. The DR method has the advantage of being able to significantly reduce the computational cost of the EnKF analysis. In the system, the lower-resolution ensemble provides the flow-dependent background error covariance, while the single-high-resolution forecast and analysis provides the benefit of higher resolution, which is important for resolving the internal structures of thunderstorms. The relative smoothness of the covariance obtained from the lower 4-km-resolution ensemble does not appear to significantly degrade the quality of analysis. This is because the cross covariance among different variables is of first-order importance for “retrieving” unobserved variables from the radar radial velocity data. For the DR analysis, an ensemble size of 40 appears to be a reasonable choice with the use of a 4-km horizontal resolution in the ensemble and a 1-km resolution in the high-resolution analysis. Several sensitivity tests show that the DR EnKF system is quite robust to different observation errors. A 4-km thinned data resolution is a compromise that is acceptable under the constraint of real-time applications. A data density of 8 km leads to a significant degradation in the analysis.

scholarly journals The definition of an atmospheric database for Aeolus

2011 ◽  
Vol 4 (1) ◽  
pp. 67-88 ◽  
Author(s):  
G. J. Marseille ◽  
K. Houchi ◽  
J. de Kloe ◽  
A. Stoffelen
Keyword(s):  
High Resolution ◽  
Meteorological Data ◽  
Sampling Strategy ◽  
Laser Wavelength ◽  
Geographic Region ◽  
Atmospheric Dynamics ◽  
Specific Humidity ◽  
Small Scale ◽  
Horizontal Line ◽  
Definition Of

Abstract. The definition of an atmospheric database is an important component of simulation studies in preparation of future earth observing remote sensing satellites. The Aeolus mission, formerly denoted Atmospheric Dynamics Mission (ADM) or ADM-Aeolus, is scheduled for launch end of 2013 and aims at measuring profiles of single horizontal line-of-sight (HLOS) wind components from the surface up to about 32 km with a global coverage. The vertical profile resolution is limited but may be changed during in-orbit operation. This provides the opportunity of a targeted sampling strategy, e.g., as a function of geographic region. Optimization of the vertical (and horizontal) sampling strategy requires a characterization of the atmosphere optical and dynamical properties, more in particular the distribution of atmospheric particles and their correlation with the atmospheric dynamics. The Aeolus atmospheric database combines meteorological data from the ECMWF model with atmosphere optical properties data from CALIPSO. An inverse algorithm to retrieve high-resolution particle backscatter from the CALIPSO level-1 attenuated backscatter product is presented. Global weather models tend to underestimate atmospheric wind variability. A procedure is described to ensure compatibility of the characteristics of the database winds with those from high-resolution radiosondes. The result is a high-resolution database of zonal, meridional and vertical wind, temperature, specific humidity and particle and molecular backscatter and extinction at 355 nm laser wavelength. This allows the simulation of small-scale atmospheric processes within the Aeolus observation sampling volume and their impact on the quality of the retrieved HLOS wind profiles. The database extends over four months covering all seasons. This allows a statistical evaluation of the mission components under investigation. The database is currently used for the development of the Aeolus wind processing, the definition of wind calibration strategies and the optimization of the Aeolus sampling strategy.

Detection of normal mediastinal lymph nodes by ultrasonography

1997 ◽  
Vol 38 (6) ◽  
pp. 965-969 ◽  
Author(s):  
C. F. Dietrich ◽  
M. Liesen ◽  
R. Buhl ◽  
G. Herrmann ◽  
J. Kirchner ◽  
...  
Keyword(s):  
High Resolution ◽  
Lymph Nodes ◽  
Pathological Finding ◽  
Doppler Imaging ◽  
Colour Doppler Imaging ◽  
Asymptomatic Volunteers ◽  
Human Cadavers ◽  
Mean Size ◽  
Almost All ◽  
Node Diameter

Purpose: the detection by US (ín contrast to CT) of lymph nodes of any size in the mediastinum is usually considered to be a pathological finding. the aim of this study was to find out whether it was possible to detect normal lymph nodes by high-resolution mediastinal US Material and Methods: Six different mediastinal regions in 80 healthy asymptomatic volunteers and in 20 human cadavers were examined by means of US (with colour Doppler imaging) to assess US access to the respective regions and to demonstrate the number and size of detectable lymph nodes. All the cadaveric lymph nodes that were detected were examined histologically to exclude inflammatory or malignant infiltration Results: in almost all subjects, we obtained US access to the supra-aortic (100%), paratracheal (95%), prevascular (99%), and pencardial (98%) regions, and to the aorticopulmonary window (98%). US access to the subcarinal region was more difficult (75%). in the healthy subjects, lymph nodes were detected in the paratracheal region (in 35% of these subjects, mean lymph-node diameter 12×7 mm), in the aorticopulmonary window (45%, 14×8 mm), and in the subcarinal region (13%, 13×7 mm). in the cadavers, histologically normal lymph nodes were detected frequently in the paratracheal region (85%, mean size 11×6 mm) and in the aorticopulmonary window (90%, 11×5 mm) Conclusion: These results indicate that normal lymph nodes (and not only pathological lymph nodes) can be demonstrated by high-resolution mediastinal US

Remote Sensing Image Mosaic Algorithm

2012 ◽  
Vol 500 ◽  
pp. 716-721
Author(s):  
Yi Ding Wang ◽  
Shuai Qin
Keyword(s):  
Remote Sensing ◽  
High Resolution ◽  
Hot Spot ◽  
Remote Sensing Image ◽  
Processing Algorithm ◽  
Geometric Features ◽  
Image Mosaic ◽  
Post Processing ◽  
Remote Sensing Images ◽  
Image Pixels

In the field of remote sensing, the acquirement of higher resolution of remote sensing images has become a hot spot issue with widely use of high resolution of remote sensing images. This paper focus on the characteristics of high resolution remote sensing images, on the basis of fully considerate of the correlation between geometric features and image pixels, bring forward a fusion of image mosaic processing algorithm. With this algorithm, the surface features can be well preserved after the processing of mosaic the remote sensing images, and the overlapping area can transit naturally, it will be better for the post-processing, analysis and application.

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