scholarly journals An overall view of temperature oscillations in the solar chromosphere with ALMA

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200174 ◽  
Author(s):  
S. Jafarzadeh ◽  
S. Wedemeyer ◽  
B. Fleck ◽  
M. Stangalini ◽  
D. B. Jess ◽  
...  
Keyword(s):  
Field Of View ◽  
High Temporal Resolution ◽  
Solar Chromosphere ◽  
Gas Temperature ◽  
Frequency Distributions ◽  
Wave Dynamics ◽  
Solar Observations ◽  
Temperature Oscillations ◽  
Direct Measurements ◽  
Dominant Frequencies

By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb–Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3–5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of H α line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals The solar chromosphere at millimetre and ultraviolet wavelengths

2019 ◽  
Vol 622 ◽  
pp. A150 ◽  
Author(s):  
S. Jafarzadeh ◽  
S. Wedemeyer ◽  
M. Szydlarski ◽  
B. De Pontieu ◽  
R. Rezaei ◽  
...  
Keyword(s):  
Numerical Models ◽  
Active Regions ◽  
Uv Spectra ◽  
Solar Chromosphere ◽  
Solar Observations ◽  
Direct Measurements ◽  
The Mean ◽  
Far Ultraviolet ◽  
Temperature Maps ◽  
Imaging Spectrograph

Solar observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide us with direct measurements of the brightness temperature in the solar chromosphere. We study the temperature distributions obtained with ALMA Band 6 (in four sub-bands at 1.21, 1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of, a sunspot, comprising quasi-quiet and active regions with different amounts of underlying magnetic fields. We compare these temperatures with those obtained at near- and far-ultraviolet (UV) wavelengths (and with the line-core intensities of the optically-thin far-UV spectra), co-observed with the Interface Region Imaging Spectrograph (IRIS) explorer. These include the emission peaks and cores of the Mg II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the mid-to-high chromosphere and the low transition region. Splitting the ALMA sub-bands resulted in an slight increase of spatial resolution in individual temperature maps, thus, resolving smaller-scale structures compared to those produced with the standard averaging routines. We find that the radiation temperatures have different, though somewhat overlapping, distributions in different wavelengths and in the various magnetic regions. Comparison of the ALMA temperatures with those of the UV diagnostics should, however, be interpreted with great caution, the former is formed under the local thermodynamic equilibrium (LTE) conditions, the latter under non-LTE. The mean radiation temperature of the ALMA Band 6 is similar to that extracted from the IRIS C II line in all areas with exception of the sunspot and pores where the C II poses higher radiation temperatures. In all magnetic regions, the Mg II lines associate with the lowest mean radiation temperatures in our sample. These will provide constraints for future numerical models.

scholarly journals High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200184 ◽  
Author(s):  
J. C. Guevara Gómez ◽  
S. Jafarzadeh ◽  
S. Wedemeyer ◽  
M. Szydlarski ◽  
M. Stangalini ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
High Frequency ◽  
Small Scale ◽  
High Temporal Resolution ◽  
Solar Chromosphere ◽  
Wave Dynamics ◽  
High Frequency Oscillations ◽  
Diagnostic Potential ◽  
Kink Waves ◽  
Outer Atmosphere

We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference

2020 ◽  
Vol 12 (7) ◽  
pp. 1170 ◽  
Author(s):  
Cintia Carbajal Henken ◽  
Lisa Dirks ◽  
Sandra Steinke ◽  
Hannes Diedrich ◽  
Thomas August ◽  
...  
Keyword(s):  
Water Vapor ◽  
Pairwise Comparison ◽  
Weather Conditions ◽  
Satellite System ◽  
High Temporal Resolution ◽  
Data Sets ◽  
Frequency Distributions ◽  
Temporal Sampling ◽  
Global Navigation Satellite ◽  
Satellite Instruments

Passive imagers on polar-orbiting satellites provide long-term, accurate integrated water vapor (IWV) data sets. However, these climatologies are affected by sampling biases. In Germany, a dense Global Navigation Satellite System network provides accurate IWV measurements not limited by weather conditions and with high temporal resolution. Therefore, they serve as a reference to assess the quality and sampling issues of IWV products from multiple satellite instruments that show different orbital and instrument characteristics. A direct pairwise comparison between one year of IWV data from GPS and satellite instruments reveals overall biases (in kg/m 2 ) of 1.77, 1.36, 1.11, and −0.31 for IASI, MIRS, MODIS, and MODIS-FUB, respectively. Computed monthly means show similar behaviors. No significant impact of averaging time and the low temporal sampling on aggregated satellite IWV data is found, mostly related to the noisy weather conditions in the German domain. In combination with SEVIRI cloud coverage, a change of shape of IWV frequency distributions towards a bi-modal distribution and loss of high IWV values are observed when limiting cases to daytime and clear sky. Overall, sampling affects mean IWV values only marginally, which are rather dominated by the overall retrieval bias, but can lead to significant changes in IWV frequency distributions.

The measurement and prediction of sustained temperature oscillations in a chemical reactor

1969 ◽  
Vol 309 (1496) ◽  
pp. 1-26 ◽  
Keyword(s):  
Mathematical Analysis ◽  
Methyl Chloride ◽  
Chemical Reactor ◽  
Vapour Phase ◽  
Gas Temperature ◽  
Experimental Conditions ◽  
Temperature Oscillations ◽  
Series Of Experiments ◽  
Steady Oscillations

Steady oscillations in the recorded gas temperature have been observed in a series of experiments in which the vapour-phase chlorination of methyl chloride was carried out. The instability was reproducible and persisted within a sharply defined range of reaction temperatures. A mathematical analysis of the dynamics of the reacting system is found to predict closely the nature and frequency of the oscillations and the range of experimental conditions within which they occur.

HAPS role of in Earth Observation Multi-platform Paradigm for Environmental Monitoring

2020 ◽  
Author(s):  
Giuseppe Persechino ◽  
Vincenzo Baraniello ◽  
Sara Parrilli ◽  
Francesco Tufano ◽  
Guido Rianna
Keyword(s):  
Environmental Monitoring ◽  
Spatial Resolution ◽  
Large Scale ◽  
Field Of View ◽  
High Temporal Resolution ◽  
Natural Ecosystems ◽  
Data Types ◽  
Spatial And Temporal Scales ◽  
The Individual ◽  
Hybrid Configuration

<p>Environmental monitoring often requires the observation of phenomena at different spatial and temporal scales. For example, to study the anthropic impact on natural ecosystems, it is necessary both to evaluate its effects on a large scale and to detect and recognize the environmental criticalities that, locally, determine these effects. These needs impose tight requirements on data temporal, spatial and spectral resolution that a single aerospace platform can hardly satisfy. Therefore, it is necessary to develop new collaborative paradigms between different platforms to improve their observation capabilities, exploiting interoperability between heterogeneous platforms and sensors. However, even multi-platform approaches, due to the limitations of the individual platforms currently available in terms of revisit time and sensor spatial resolution, cannot fully comply with the requirements imposed by some specific environmental issues at acceptable costs.</p><p>In this paper, HAPS (High Altitude Pseudo-Satellite) use is proposed as a tool to overcome these limitations and to extend the applicability of the multi-platform paradigm. </p><p>In environmental monitoring context, one of the main advantages offered by HAPSs consists in the possibility of providing data with higher spatial resolution than satellites, and at lower cost compared to aerial platforms. Moreover, HAPSs offer a larger field of view than UAVs and can provide data types such as fluorescence or hyperspectral ones that, because of sensor weight and cost, rarely could be acquired by UAVs. Finally, HAPS platforms, thanks to their station-keeping capability on a desired area, offer the possibility of having data with a high temporal resolution to monitor the temporal evolution of phenomena at a rate currently not possible with other platforms.</p><p>Different HAPS configurations have been proposed, based on aerostatic or aerodynamic forces. CIRA is designing a HAPS that, thanks to its hybrid configuration, is able to generate aerodynamic and aerostatic forces. It could fly at an altitude of 18-20 km, from this altitude range, the field of view has a diameter length of about 600 km. Maintenance and updating of its equipment and payload is also possible because the platform can land and take-off again.</p><p>CIRA is also designing the platform payload. The design goal is to define a new wide-area sensor based on visible, thermal, or hyperspectral cameras, with a better resolution than satellites. In this way, it will be possible to detect environmental anomalies in persistence in order to alert the other platforms. A very high focal second-reading sensor will also be used to avoid false-positive alerts.         </p><p>In this paper, we will present the main characteristics of HAPS platforms and how they, in synergy with other ones, would lead to considerable advantages in environmental monitoring. In particular, we will discuss the multi-platform paradigm, the current platform limits and their influence on the paradigm effectiveness in the context of environmental monitoring, characteristics of the HAPS platform that CIRA is currently conceptually designing in the context of the OT4clima Project and the main issues relative to its payload design.</p>

scholarly journals Chromospheric heating during flux emergence in the solar atmosphere

2018 ◽  
Vol 612 ◽  
pp. A28 ◽  
Author(s):  
Jorrit Leenaarts ◽  
Jaime de la Cruz Rodríguez ◽  
Sanja Danilovic ◽  
Göran Scharmer ◽  
Mats Carlsson
Keyword(s):  
Linear Polarization ◽  
Active Regions ◽  
Spatial And Temporal Variation ◽  
Solar Chromosphere ◽  
Gas Temperature ◽  
Horizontal Magnetic Field ◽  
Magnetic Elements ◽  
Spatially Extended ◽  
Non Local ◽  
Radiative Losses

Context. The radiative losses in the solar chromosphere vary from 4 kW m−2 in the quiet Sun, to 20 kW m−2 in active regions. The mechanisms that transport non-thermal energy to and deposit it in the chromosphere are still not understood. Aim. We aim to investigate the atmospheric structure and heating of the solar chromosphere in an emerging flux region. Methods. We have used observations taken with the CHROMIS and CRISP instruments on the Swedish 1-m Solar Telescope in the Ca II K , Ca II 854.2 nm, Hα, and Fe I 630.1 nm and 630.2 nm lines. We analysed the various line profiles and in addition perform multi-line, multi-species, non-local thermodynamic equilibrium (non-LTE) inversions to estimate the spatial and temporal variation of the chromospheric structure. Results. We investigate which spectral features of Ca II K contribute to the frequency-integrated Ca II K brightness, which we use as a tracer of chromospheric radiative losses. The majority of the radiative losses are not associated with localised high-Ca II K-brightness events, but instead with a more gentle, spatially extended, and persistent heating. The frequency-integrated Ca II K brightness correlates strongly with the total linear polarization in the Ca II 854.2 nm, while the Ca II K profile shapes indicate that the bulk of the radiative losses occur in the lower chromosphere. Non-LTE inversions indicate a transition from heating concentrated around photospheric magnetic elements below log τ500 = −3 to a more space-filling and time-persistent heating above log τ500 = −4. The inferred gas temperature at log τ500 = −3.8 correlates strongly with the total linear polarization in the Ca II 854.2 nm line, suggesting that that the heating rate correlates with the strength of the horizontal magnetic field in the low chromosphere.

scholarly journals Can posterior teeth of patients be translated buccally, and does bone form on the buccal surface in response?

2015 ◽  
Vol 86 (4) ◽  
pp. 527-534 ◽  
Author(s):  
Chad J. Capps ◽  
Phillip M. Campbell ◽  
Byron Benson ◽  
Peter H. Buschang
Keyword(s):  
Tooth Movement ◽  
Field Of View ◽  
Small Field ◽  
Bone Thickness ◽  
Bone Apposition ◽  
Posterior Teeth ◽  
Direct Measurements ◽  
Control Forces ◽  
Bone Height ◽  
Small Field Of View

ABSTRACT Objective:  To produce buccal translation and determine whether buccal bone forms on the cortical surfaces. Materials and Methods:  Eleven patients requiring maxillary first premolar extractions participated in this prospective, randomized, split-mouth study. Pre- and posttreatment records included models, photographs, and small field of view CBCT images. One randomly chosen maxillary first premolar was moved buccally with 50 g of force applied approximately at the tooth’s center of resistance. The other premolar served as the control. Forces were re-activated every 3 weeks for approximately 9 weeks, after which the teeth were held in place for 3 weeks. Pre- and posttreatment records were analyzed and superimposed to evaluate changes in the dental-alveolar complex. Results:  There was significant (P < .05) movement of the experimental premolar with minimal buccal tipping (2.2°). Changes in maximum bone height were bimodal, with 6 patients showing 0.42 mm and 5 patients showing 8.3 mm of vertical bone loss. Buccal bone thickness 3 mm apical to the CEJ decreased 0.63 mm. Direct measurements and CBCT superimpositions showed that buccal bone over the roots grew 0.46 mm and 0.51 mm, respectively. Conclusions:  It is possible to produce buccal bodily tooth movement with only limited amounts of tipping. Such movements are capable of producing buccal bone apposition, but there are potential limitations.

scholarly journals Instrument concepts for the observation of prominences with future ground-based telescopes

2013 ◽  
Vol 8 (S300) ◽  
pp. 370-375 ◽  
Author(s):  
A. López Ariste
Keyword(s):  
Image Quality ◽  
Magnetic Fields ◽  
Atmospheric Turbulence ◽  
Temporal Resolution ◽  
Field Of View ◽  
Large Field ◽  
Solar Observations ◽  
New Generation

AbstractThe observation of prominences with ground-based telescopes suffers from poor image quality due to atmospheric turbulence when compared with space-borne instruments which, for solar observations, are of similar apertures. To make ground-based instruments competitive, they should rely on spectropolarimetry and the measurement of prominence magnetic fields, a task which no foreseable space instrument will perform. But spectropolarimetry alone does not suffice, and we argue that future instrumentation should combine it with imaging in a large field of view and good temporal resolution. We place numbers on those requirements and give examples of instrumental accomplishments already at work today that forecast a new generation of instruments for the observation of prominences from ground-based telescopes.

scholarly journals Characteristics of cloud liquid water path from SEVIRI onboard the Meteosat Second Generation 2 satellite for several cloud types

2014 ◽  
Vol 7 (4) ◽  
pp. 887-905 ◽  
Author(s):  
A. Kniffka ◽  
M. Stengel ◽  
M. Lockhoff ◽  
R. Bennartz ◽  
R. Hollmann
Keyword(s):  
Diurnal Cycle ◽  
Liquid Water ◽  
Second Generation ◽  
Cloud Amount ◽  
Field Of View ◽  
Relative Amplitude ◽  
Cloud Type ◽  
Liquid Water Path ◽  
Frequency Distributions ◽  
Water Path

Abstract. In this study the temporal and spatial characteristics of the liquid water path (LWP) of low, middle and high level clouds are analysed using space-based observations from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument onboard the Meteosat Second Generation 2 (MSG 2) satellite. Both geophysical quantities are part of the CLAAS (CLoud property dAtAset using SEVIRI) data set and are generated by EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF). In this article we focus on the statistical properties of LWP, retrieved during daylight conditions, associated with individual cloud types. We analysed the intrinsic variability of LWP, that is, the variability in only cloudy regions and the variations driven by cloud amount. The relative amplitude of the intrinsic diurnal cycle exceeded the cloud amount driven amplitude in our analysed cases. Our results reveal that each cloud type possesses a characteristic intrinsic LWP distribution. These frequency distributions are constant with time in the entire SEVIRI field of view, but vary for smaller regions like Central Europe. Generally the average LWP is higher over land than over sea; in the case of low clouds this amounts to 15–27% in 2009. The variance of the frequency distributions is enhanced as well. Also, the average diurnal cycle of LWP is related to cloud type with the most pronounced relative diurnal variations being detected for low and middle level clouds. Maps of the relative amplitude and the local time of maximum LWP show the variation throughout the SEVIRI field of view.

scholarly journals High-efficiency, large-area lattice light-sheet generation by dielectric metasurfaces

Nanophotonics ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 4043-4051
Author(s):  
Fenghua Shi ◽  
Jing Wen ◽  
Dangyuan Lei
Keyword(s):  
Spatial Resolution ◽  
Temporal Resolution ◽  
High Efficiency ◽  
Numerical Aperture ◽  
Light Sheet ◽  
Field Of View ◽  
Objective Lens ◽  
High Temporal Resolution ◽  
Light Sheet Microscopy ◽  
Illumination Efficiency

AbstractLattice light-sheet microscopy (LLSM) was developed for long-term live-cell imaging with ultra-fine three-dimensional (3D) spatial resolution, high temporal resolution, and low photo-toxicity by illuminating the sample with a thin lattice-like light-sheet. Currently available schemes for generating thin lattice light-sheets often require complex optical designs. Meanwhile, limited by the bulky objective lens and optical components, the light throughput of existing LLSM systems is rather low. To circumvent the above problems, we utilize a dielectric metasurface of a single footprint to replace the conventional illumination modules used in the conventional LLSM and generate a lattice light-sheet with a ~3-fold broader illumination area and a significantly leveraged illumination efficiency, which consequently leads to a larger field of view with a higher temporal resolution at no extra cost of the spatial resolution. We demonstrate that the metasurface can manipulate spatial frequencies of an input laser beam in orthogonal directions independently to break the trade-off between the field of view and illumination efficiency of the lattice light-sheet. Compared to the conventional LLSM, our metasurface module serving as an ultra-compact illumination component for LLSM at an ease will potentially enable a finer spatial resolution with a larger numerical-aperture detection objective lens.

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