Acoustic Wave Heating Research Articles

Constraining the Systematics of (Acoustic) Wave Heating Estimates in the Solar Chromosphere

Acoustic wave heating is believed to contribute significantly to the missing energy input required to maintain the solar chromosphere in its observed state. We studied the propagation of waves above the acoustic cutoff in the upper photosphere into the chromosphere with ultraviolet and optical spectral observations interpreted through comparison with 3D radiative magnetohydrodynamic Bifrost models to constrain the heating contribution from acoustic waves in the solar atmosphere. Sit-and-stare observations taken with the Interface Region Imaging Spectrograph and data from the Interferometric BIdimensional Spectrograph were used to provide the observational basis of this work. We compared the observations with synthetic observables derived from the Bifrost solar atmospheric model. Our analysis of the Bifrost simulations show that internetwork and enhanced-network regions exhibit significantly different wave-propagation properties, which are important for accurate wave flux estimates. The inferred wave energy fluxes based on our observations are not sufficient to maintain the solar chromosphere. We point out that the systematics of the modeling approaches in the literature lead to differences which could determine the conclusions of this type of study, based on the same observations.

Spatio-temporal analysis of chromospheric heating in a plage region

Context. Our knowledge of the heating mechanisms that are at work in the chromosphere of plage regions remains highly unconstrained from observational studies. While many heating candidates have been proposed in theoretical studies, the exact contribution from each of them is still unknown. The problem is rather difficult because there is no direct way of estimating the heating terms from chromospheric observations. Aims. The purpose of our study is to estimate the chromospheric heating terms from a multi-line high-spatial-resolution plage dataset, characterize their spatio-temporal distribution and set constraints on the heating processes that are at work in the chromosphere. Methods. We used nonlocal thermodynamical equilibrium inversions in order to infer a model of the photosphere and chromosphere of a plage dataset acquired with the Swedish 1-m Solar Telescope (SST). We used this model atmosphere to calculate the chromospheric radiative losses from the main chromospheric cooler from H I, Ca II, and Mg II atoms. In this study, we approximate the chromospheric heating terms by the net radiative losses predicted by the inverted model. In order to make the analysis of time-series over a large field of view computationally tractable, we made use of a neural network which is trained from the inverted models of two non-consecutive time-steps. We have divided the chromosphere in three regions (lower, middle, and upper) and analyzed how the distribution of the radiative losses is correlated with the physical parameters of the model. Results. In the lower chromosphere, the contribution from the Ca II lines is dominant and predominantly located in the surroundings of the photospheric footpoints. In the upper chromosphere, the H I contribution is dominant. Radiative losses in the upper chromosphere form a relatively homogeneous patch that covers the entire plage region. The Mg II also peaks in the upper chromosphere. Our time analysis shows that in all pixels, the net radiative losses can be split in a periodic component with an average amplitude of amp̅Q = 7.6 kW m−2 and a static (or very slowly evolving) component with a mean value of −26.1 kW m−2. The period of the modulation present in the net radiative losses matches that of the line-of-sight velocity of the model. Conclusions. Our interpretation is that in the lower chromosphere, the radiative losses are tracing the sharp lower edge of the hot magnetic canopy that is formed above the photosphere, where the electric current is expected to be large. Therefore, Ohmic current dissipation could explain the observed distribution. In the upper chromosphere, both the magnetic field and the distribution of net radiative losses are room-filling and relatively smooth, whereas the amplitude of the periodic component is largest. Our results suggest that acoustic wave heating may be responsible for one-third of the energy deposition in the upper chromosphere, whereas other heating mechanisms must be responsible for the rest: turbulent Alfvén wave dissipation or ambipolar diffusion could be among them. Given the smooth nature of the magnetic field in the upper chromosphere, we are inclined to rule out Ohmic dissipation of current sheets in the upper chromosphere.

Tunable Optical Properties of 2D Materials and Their Applications

AbstractRecent efforts have been heavily devoted to the development of next‐generation optoelectronic devices based on 2D materials, due to their unique optical properties that are distinctly different from those of bulk counterparts. Given that the feature of flexible tunability is highly desired, various approaches have been demonstrated to efficiently modulate the optical properties, eventually enabling peculiar functionalities or realizing high‐performance nanoscale devices. Here, this review focuses on recent advances in tuning the optical properties of 2D materials by external stimuli including electric field, mechanical strain, magnetic field, acoustic wave, and thermal heating. Also, such tunability leads to many emerging applications in the fields of electronics, optics, sensors, and energy harvesting, which are summarized and critically discussed in the paper.

Spatio-temporal evolution of electric field inside a microwave discharge plasma during initial phase of ignition and its effect on power coupling

During the initial phase of microwave (MW) power launch inside a MW discharge ion source (MDIS), plasma and the electric fields are evolved with time together in the plasma volume. The spatio-temporal evolution pattern in the cavity of a MDIS is reported here, highlighting the role of these electric fields on power coupling processes. Evolution of electric field and so power coupling processes are calculated using Finite Element Method (FEM). Unlike PIC/MCC or hybrid fluid, here FEM model uses time dependent Poisson solver through drift-diffusion approach. In presence of plasma gradient in the volume ambipolar electric field is generated which interacts with the MW electric field to form resultant total electric field which continuously vary during this evolution period. It is observed that main power coupling mechanism is electron cyclotron resonance (ECR) method, however with the evolution of plasma, the mode shifts from ECR to off-ECR type heating with time. Off-ECR heating in the form of upper-hybrid resonance (UHR) method, electro-static (ES) ion acoustic wave heating method are important heating mechanisms during the over-dense plasma condition, when density is above critical density for launched MW frequency, 2.45 GHz. An indirect verification of simulated temporal evolution of hot electron temperature and plasma density with the experiment, is done under similar configuration and operating environment. The experimental results are found to be agreed reasonably well with the simulation in the low power range.

Acoustic Disturbances in Galaxy Clusters

Abstract Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is the dissipation of acoustic waves generated by active galactic nuclei. Fabian et al. showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self-limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semicollisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian et al. remains the most viable path to acoustic wave heating of galaxy cluster cores.

A Microreactor With Surface Acoustic Wave Micro-Heating System

A new microreactor with surface acoustic wave (SAW) heating system was presented. The microreactor is comprised of surface acoustic wave heating source, a PDMS micro-vessel and a metal micro-vessel. An interdigital transducer (IDT) and a reflector were fabricated on a 1280 yx-LiNbO3 piezoelectric substrate by microelectric technology. A RF signal with 27.5 MHz frequency was applied to the IDT to generate surface acoustic wave. When hitting a glycerin microfluid in the PDMS micro-vessel on the piezoelectric substrate, SAW radiated into the glycerin microfluid and heated it. Then, the temperature of the reactants in the metal micro-vessel was raised by heating transfer. The experiments of melting solid paraffin and color development reaction have been examined using the microreactor. The results show that the temperature of the reactants in the metal micro-vessel can be raised at least 42°C, which is enough for lots of biochemical reactions. The results also show that the microreactor can greatly improve the reaction velocity of color development reaction due to SAW radiation. This work is valuable for biochemical analysis on microfluidic device.

Can High Frequency Acoustic Waves Heat the Quiet Sun Chromosphere?

Abstract We use Hinode/SOT Ca II H-line and blue continuum broadband observations to study the presence and power of high frequency acoustic waves at high spatial resolution. We find that there is no dominant power at small spatial scales; the integrated power using the full resolution of Hinode ($0\rlap{.}^{\prime\prime}05$ pixels, $0\rlap{.}^{\prime\prime}16$ resolution) is larger than the power in the data degraded to $0\rlap{.}^{\prime\prime}5$ pixels (TRACE pixel size) by only a factor of 1.2. At 20 mHz the ratio is 1.6. Combining this result with the estimates of the acoustic flux based on TRACE data of Fossum and Carlsson (2006, ApJ, 646, 579), we conclude that the total energy flux in acoustic waves of frequency 5–40 mHz entering the internetwork chromosphere of the quiet Sun is less than 800 Wm$^{-2}$, inadequate to balance the radiative losses in a static chromosphere by a factor of five.

Sunspot Chromospheric Heating by Kinetic Alfvén Waves

Sunspot atmospheric models show that sunspots have a higher temperature than the surrounding quiet Sun in the upper chromosphere, although they are dark in the photosphere. This Letter presents a comparison between acoustic wave heating and kinetic Alfven wave (KAW) heating in sunspots from the photosphere through the chromosphere based on a semiempirical model calculated by non-LTE procedure. The result suggests that acoustic wave heating is still a possible dominating mechanism in the photosphere and in the lower chromosphere below 850 km, similar to previous works. But in the upper chromosphere above 850 km, KAW heating is a more promising candidate that dominates sunspot chromospheric heating. We speculate that this probably relates to the ionization exceeding one in a thousand in the upper chromosphere, so that the plasma processes such as KAW dissipation play an important role in the atmospheric dynamics.

Physical processes in acoustic wave heating of the thermosphere

Upward propagating acoustic waves heat the atmosphere at essentially all heights due to effects of viscous dissipation, sensible heat flux divergence, and Eulerian drift work. Acoustic wave‐induced pressure gradient work provides a cooling effect at all heights, but this is overwhelmed by the heating processes. Eulerian drift work and wave‐induced pressure gradient work dominate the energy balance, but they nearly cancel at most altitudes, leaving their difference, together with viscous dissipation and sensible heat flux divergence to heat the atmosphere. Acoustic waves are very different from gravity waves which cool the upper atmosphere through the effect of sensible heat flux divergence. Acoustic wave dissipation could be an important source of upper atmospheric heating.

Heating of Jupiter’s thermosphere by the dissipation of upward propagating acoustic waves

Thunderstorms in Jupiter’s atmosphere are likely to be prodigious generators of acoustic waves, as are thunderstorms in Earth’s atmosphere. Accordingly, we have used a numerical model to study the dissipation in Jupiter’s thermosphere of upward propagating acoustic waves. Model simulations are performed for a range of wave periods and horizontal wavelengths believed to characterize these acoustic waves. The possibility that the thermospheric waves observed by the Galileo Probe might be acoustic waves is also investigated. Whereas dissipating gravity waves can cool the upper thermosphere through the effects of sensible heat flux divergence, it is found that acoustic waves mainly heat the Jovian thermosphere through effects of molecular dissipation, sensible heat flux divergence, and Eulerian drift work. Only wave-induced pressure gradient work cools the atmosphere, an effect that operates at all altitudes. The sum of all effects is acoustic wave heating at all heights. Acoustic waves and gravity waves heat and cool the atmosphere in fundamentally different ways. Though the amplitudes and mechanical energy fluxes of acoustic waves are poorly constrained in Jupiter’s atmosphere, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at a significant rate, tens to a hundred Kelvins per day, and thereby account for the high temperatures of Jupiter’s upper atmosphere. It is unlikely that the waves detected by the Galileo Probe were acoustic waves; if they were, they would have heated Jupiter’s thermosphere at enormous rates.

Acoustic and magnetic wave heating in stars

Theoretical chromospheric models described in the two previous papers of this series are used to study the relationship between the chromospheric emission and the lling factor. This theoretically determined rela- tionship shows that the chromospheric emission flux in Ca II (H+K) is approximately proportional to the square root of the magnetic lling factor at the stellar surface. To relate the lling factor to stellar rotation rate, we compare the theoretical fluxes with observations of stars with known rotation period. The comparison shows that the Rossby number is probably a more appropriate measure of the rotation influence on activity of main-sequence stars than the rotation period. Our theoretical Mg II (h+k) and Ca II (H+K) emission fluxes are also found to be well correlated, which is in a good agreement with the observational data.

Acoustic and magnetic wave heating in stars

In the first paper of this series we developed a method to construct theoretical, time-dependent and two-component chromosphere models for late-type main sequence stars. The models consist of non-magnetic regions heated by acoustic waves and magnetic flux tube regions heated by magnetic tube waves. By specifying the magnetic filling factor, theoretical models of stellar atmospheres with different chromospheric activity can be calculated. Here, these models are used to simulate the emerging Ca II and Mg II chromospheric emission fluxes and compare them with observations. The comparison shows that the wave heating alone can explain most but not all of the observed range of chromospheric activity. In addition, the results obtained clearly imply that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave (e.g., reconnective) heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres.

Acoustic and magnetic wave heating in stars

We describe a method to construct theoretical, time-dependent, two-component and wave heated chromosphere models for late-type dwarfs. The models depend only on four basic stellar parameters: effective temperature, gravity, metallicity and filling factor, which determines the coverage of these stars by surface magnetic fields. They consist of non-magnetic regions heated by acoustic waves and vertically oriented magnetic flux tubes heated by longitudinal tube waves with contributions from transverse tube waves. Acoustic, longitudinal and transverse wave energy spectra and fluxes generated in stellar convection zones are computed and used as input parameters for the theoretical models. The waves are allowed to propagate and heat both components by shock dissipation. We compute the time-dependent energy balance between the dissipated wave energy and the most prominent chromospheric radiative losses as function of height in the stellar atmosphere. For the flux tube covered stars, the emerging radiative fluxes in the Ca II and Mg II lines are computed by using a newly developed multi-ray radiative transfer method.

Wave Heating and Range of Stellar Activity in Late-Type Dwarfs

Theoretical time-dependent and two-component chromospheric models for late-type dwarfs are constructed based on acoustic and magnetic wave heating mechanisms. The models are used to predict the theoretical range of chromospheric activity for these stars. Comparison of this range with the one established observationally shows that the wave heating alone can explain most but not all of the observed range of stellar activity.

Acoustic wave heating of the thermosphere

A numerical model is used to study the dissipation in the thermosphere of upward propagating acoustic waves. Whereas dissipating gravity waves can cool the upper atmosphere through the effects of sensible heat flux divergence, it is found that acoustic waves mainly heat the thermosphere by viscous dissipation. Though the amplitudes of acoustic waves in the atmosphere are poorly constrained, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at rates of tens of kelvins per day and thereby contribute to the thermospheric energy balance. It is shown that viscous heating cannot be calculated from the divergence of the wave mechanical energy flux. Acoustic waves that are barely detectable at mesopause heights can become significant heaters of the atmosphere high in the thermosphere. We suggest that acoustic waves might be responsible for heating the equatorial F region to produce the hot spot observed in the O I 630 nm airglow over the Andes Mountains.

On Chromospheric Heating Mechanisms of “Basal Flux” Stars

Several pieces of evidence have been pieced together over recent years to support the notion that the chromospheric emission measured from stars with convection zones results in part from the upward propagation and dissipation of acoustic waves. One argument, based on a statistical analysis of available UV data of such stars across the H-R diagram, suggests the presence of an omnipresent "basal" level of chromospheric heating, which has been postulated as resulting from nonlinear acoustic wave heating.

Physical processes determining the chromospheric temperature distribution

Calculations performed with several models of the solar chromosphere support Ulmschneider's conclusion that relatively short period acoustic waves heat the low chromosphere in the region just above the temperature minimum. However, these same short period waves (10⩽ period P⩽80 s) are not able to maintain chromospheric temperatures at heights where τ5000A(normal) < 10-6. The calculations also show that an earlier conjecture stating that the H2 population might influence the non-LTE chromospheric H- population is probably not correct, due to lower values of the ratio ne/nH inferred from more recent observations. Finally, the calculations support Athay's contention that the Cayrel mechanism alone cannot produce the observed temperature rise, because the magnitude of the radiative cooling in the lines is too great.