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1.
Climatic temperature changes at the ground surface propagate downward to the subsurface creating transient disturbances to the temperature—depth (T(z)) profile. Due to the poor thermal diffusivity of rocks the disturbances are preserved long times in the bedrock, and in a conductive regime it is possible to reveal the ground surface temperature (GST) history from borehole temperature data with inversion techniques. Geothermal temperature measurements thus provide a source of palaeoclimatic information which so far has not been utilized extensively. Inversion of GST history is, however, not straightforward and any disturbing effects should be excluded before the data can be utilized in inversion. Groundwater flow is of special importance in this respect because it is a common phenomenon in bedrock and convection often produces temperature—depth profiles resembling those affected by palaeoclimatic GST changes. In interpreting temperature—depth (T(z)) logs it is therefore not always clear whether the recorded vertical gradient variations should be attributed to the effects of palaeoclimatic ground surface temperature (GST) changes or to groundwater circulation. Using several synthetic T(z) profiles and applying general least squares inversion techniques we simulate a situation of “misinterpreting” the curvature of the T(z) profile in terms of palaeoclimatic GST changes, although it is actually produced by convective heat transfer due to groundwater flow. For comparison the opposite case is also studied, namely, genuine palaeoclimatic effects are misinterpreted as being due to disturbances caused by groundwater flow. A homogeneous half-space model is used to model T(z) profiles disturbed conductively by GST changes during the time interval 10–10000 yr B.P. and a one-dimensional porous layer model is applied for convective heat transfer calculations. The results indicate that a given T(z) profile can be attributed to either of these effects with reasonable parameter values. In addition to the synthetic T(z) profiles, a case history from a 958 m deep drill hole at Lavia, southwestern Finland, is presented. Special care is needed in analyzing T(z) data. A knowledge of geothermal data, such as temperature, thermal conductivity and diffusivity is not necessarily adequate for determining which of the phenomena (or whether a combination of them) provides the most probable interpretation of a T(z) profile. Additional information on the hydrogeological properties of the drilled strata is essential. 相似文献
2.
R. Meissner 《Earth, Moon, and Planets》1975,12(2):179-191
Based on the selenothermsT(z) (= temperature-depth functions) and melting point-depth functionsT m(z) viscosity valuesη(z) are calculated. According to two different creep laws used, two sets of viscosity values are obtained. Viscosities in the outer part of the Moon are found to be larger than those anywhere on Earth. These high values ofη explain the large elasticityQ found in lunar seismograms. Viscosities below about 500 km in depth are so small that, at present, some kind of convection or a flow of matter is possible. Tidegenerated moonquakes at depths of around 1000 km seem to be connected with some viscous process. From considerations of viscosities at the time period of mare filling, some selection of ancient selenotherms may be performed. 相似文献
3.
T. Takakura 《Solar physics》1984,91(2):311-324
In some gradual hard X-ray bursts with high intensity, hard X-ray source (15–40 keV) is steadily located in the corona along with softer X-ray source (5–10 keV).Two stationary models, high density and high temperature models, are proposed to solve the difficult problem of confinement of hot (or nonthermal) plasma in the direction of the magnetic field along the loops in the corona. In both models, an essential point is that the effective X-ray source is composed of fine dense filamentary loops imbeded in a larger rarefied coronal loop, and the electron number density in the filaments is so high as 1011–1012 cm-3. If the density is so high heat conduction can be as reasonably small as of the order of 1027 erg s -1 for the given emission measures of observed X-rays, since the required cross-sectional area is small and also classical conduction is valid. Collisional confinement of thermal tail, and nonthermal electrons if any, up to 50–60 keV in the filaments is also possible, so that the hard X-ray images can be loop like structure instead of double source (foot points).High density model is applicable to the coronal filamentary loops with temperature T
m < 5 × 107 K at the loop summit. The heat flow from the summit downwards is lost almost completely by the radiation from the loop during the conduction to the foot points. A continuous energy release is assumed near the summit to maintain the stationary temperature T
m, and pressure balance is maintained along the loop. In this model, the number density at the summit is given by n
m - 106
T
m
2
/sm, where s
m is the length of the loop from the summit to the foot point, and the distribution of temperature and density along the loop are given by T = T
m(s/sm)1/3 and n = n
m(s/sm)-1/3, respectively.High temperature model is applicable to the filamentary loops with higher temperature up to about 108.5 K and comparatively lower number density as 1011 cm-3 for the requirement of magnetic confinement of the hot plasma in radial direction. The radiation from the loop is negligibly small in this model so that the heat flux is nearly conserved down to the foot points. In this case, temperature gradient is smaller than that of the high density model, depending on the tapering of the magnetic bottle.In both models, the differential emission measure is maximum at the highest temperature T
m and the brightness distribution along the loop shows a maximum around the summit of the loop if some magnetic tapering is taken into account. 相似文献
4.
Decomposition of the product of functions like exp (– 0/z)S
+(z) [S
+(z =
0
1
P(x) dx/(x–z)], obtained by Das Gupta (1978) and relevant to the solution of equations of radiative transfer or of transfer problems in finite media by Wiener-Hopf technique, is reviewed and transformed to quite simple integral forms amenable to easy numerical evaluations. The same forms are then shown to be directly obtainable in one step under a slightly stronger condition consistent with practical cases. 相似文献
5.
The data from the Apollo-14 and Apollo-16 Active Seismic Experiments have been reanalyzed and show that a power-law velocity variation with depth,v(z)110z
1/6 m s–1 (0<z<10 m), is consistent with both the travel times and amplitudes of the first arrivals for source-to-geophone separations up to 32 m. The data were improved by removing spurious glitches, by filtering and stacking. While this improved the signal-to-noise ratios, it was not possible to measure the arrival times or amplitudes of the first arrivals beyond 32 m. The data quality precludes a definitive distinction between the power-law velocity variation and the layered-velocity model proposed previously. However, the physical evidence that the shallow lunar regolith is made up of fine particles adds weight to the 1/6-power velocity model because this is the variation predicted theoretically for self-compacting spheres.The 1/6-power law predicts the travel time,t(x), varies with separation,x, ast(x)=t
0(x/x
0)5/6 and, using a first-order theory, the amplitude,A(x), varies asA(x)=A
0(x/x
0)–(13–m)/12,m>1; the layervelocity model predictst(x)=t
0(x/x
0) andA(x)=A
0(x/x
0)–2, respectively. The measured exponents for the arrival times were between 0.63 and 0.84 while those for the amplitudes were between –1.5 and –2.2. The large variability in the amplitude exponent is due, in part, to the coarseness with which the amplitudes are measured (only five bits are used per amplitude measurement) and the variability in geophone sensitivity and thumper-shot strengths.A least-squares analysis was devised which uses redundancy in the amplitude data to extract the geophone sensitivities, shot strengths and amplitude exponent. The method was used on the Apollo-16 ASE data and it indicates there may be as much as 30 to 40% variation in geophone sensitivities (due to siting and coupling effects) and 15 to 20% variability in the thumper-shot strengths. However, because of the low signal-to-noise ratios in the data, there is not sufficient accuracy or redundancy in the data to allow high confidence in these results. 相似文献
6.
The distribution of pairwise distances f(l) for different dependences r(z) of the metric distance is used to reveal inhomogeneities in the spatial distribution of 201 long (T
90>2s) gamma-ray bursts with measured redshifts z. For a fractal set with dimensionality D, this function behaves asymptotically as f(l) ∼ l
D−1 for small l. Signs of fractal behavior with dimensionality D = 2.2–2.5 show up in all the models considered for the spatial distribution of the gamma-ray bursts. Several spatially distinct
groups of gamma-ray bursts are identified. The group with equatorial coordinates ranging from 23h56m to 0h49m and δ from +19° to +23° with redshifts of 0.81–0.94 is examined separately. 相似文献
7.
A method for the determination of the background radiation temperature in earlier cosmological epochs at redshiftsz>2 is discussed in detail. The method is based on the fact that in the clouds situated at cosmological distances at redshiftz the background radiation temperature must be (1+z) times more than in the modern epoch (z=0). This shall affect the level populations of the atoms, ions and molecules and, consequently, the parameters of the absorption lines observed in quasar absorption spectra. It is proposed to use the transition3
P
0–3
P
1 ofCi (=610 ) for the measurement of the background radiation temperature. Atz>2 this absorption line shifts to the millimeter radio region and can be observed by radioastronomical methods. 相似文献
8.
We present an attempt for an extension of the modified Boltzmann model, which was introduced by Callebautet al. (1982) as an improvement of the polytropic models, to the case of chemically-heterogeneous stars in equilibrium, containing H and He, by proposing a density profile of the formp=C
1
T
N
exp (–H
m(–*)/kT) +C
2
T
N
exp (–He
m(–*)/kT. Analytical properties are derived and numerical as well as analytical arguments are presented for the conclusion that this hypothesis for a density profile imposes an almost constant chemical profile to the model as a whole, thereby making it in this form unsuited for the study of heterogeneous stars. A comparison is made with the former Boltzmann model in the homogeneous limit. 相似文献
9.
A method is proposed allowing a quick self-consistent determination of both the central star parameters (effective temperature, surface gravity, stellar massetc.) and the optical thickness of a planetary nebula (PN). The method is a generalization of the well-known energy balance method. The method has been calibrated and tested using a photoionization model grid computed for this purpose. The internal accuracy of the method is estimated as 0.038dex for the effective temperature of central star and 0.076dex for the surface gravity.The problem of determination of overall energy losses in the nebula required by any kind of energy balance method is considered thoroughly. Approximate expressions are obtained, relating the overall energy losses to the sum of intensities of collisionally excited lines in the optical and ultraviolet spectral ranges and to some other nebular parameters. It is shown that neglecting the energy losses caused by directly unobservable collisional excitation of neutral hydrogen and helium may underestimate the central star temperature by 0.2 or even 0.5dex.
Generalized energy balance method is applied to a sample of 41 PN. Central star temperaturesT
GB
found by this method show an agreement withHeII Zanstra temperaturesT
z
(HeII) whereasT
z
(HI) is always less thanT
GB
or equal to it within the accuracy of the method. So, we confirm the explanation that the well-known Zanstra discrepancy is caused merely by low optical thickness of many PN in the Lyman continuum of hydrogen. The value ofT
z
(HeII) found with modern model atmospheres can be used as good approximation toT
ef
for central stars of overwhelming majority of PN whileT
z
(HI) is usually close toT
ef
for young nebulae only. 相似文献
10.
V. S. Troitskii 《Astrophysics and Space Science》1993,201(2):203-221
It is known that the correlation between the observed visible luminositym(z), angular dimension (z) of galaxies on the red shiftz and theoretical relations of the standard cosmology is possible only under the assumption that the luminosity and object dimension evolution are equal toL(z) =L
0(z + 1)3.2 andl(z) =l
0(z + 1)–2, respectively. This evolution is hypothetical, since it is defined by a theory which is not confirmed by experience. In order to solve the problem on the reality of the Universe expansion, it is sufficient to prove or disprove these conclusions using methods of measurement independent of the theory. One of these methods consists of defining the dependence of the radiation spectra of galaxies and quasars onz which evidently is proportional to the spectrum of absolute luminosityL(, z). It has subsequently been shown that the spectrum form is practically independent of the red shift - i.e., it remains constant during the lifetime of galaxies and quasars. Consequently, to explain the luminosity increase required by the standard cosmology, it is necessary to admit a completely unreal entity (at all wavelengths of the optical spectrum increase) of the radiation spectral density of (z + 1)3.2 times. We can conclude that in reality the luminosity evolution is either absent or its power index is smaller at least by an order of magnitude. It is likely, therefore, that the established is the result of an inadequate standard in cosmology.Another method is the use of the observed relations between the parameters ofL andl galaxies. A number of measurements made by different authors gives the relationlL
a
, where 0.33a1.6. It then follows thatl(z)(z + 1)3.2a
. This dependence of the galaxy dimension is inverse to the dependence predicted by the standard cosmology. Besides, in order to make a correlation between thel(z)(z + 1)3.2a
and measurements of (z), it is necessary that indices of the degree of luminosity evolution should be smaller by an order of magnitude.Thus, the luminosity increase and simultaneous decrease of galaxy and quasar dimensions predicted by the standard cosmolog are not confirmed by the direct astrophysical measurements. This discrepancy is the consequence of an incorrect hypothesis of Universe expansion and the relativistic cosmology based on it. 相似文献
11.
Hydrographic changes in the NW Arabian Sea are mainly controlled by the monsoon system. This results in a strong seasonal and vertical gradient in surface water properties, such as temperature, nutrients, carbonate chemistry and the isotopic composition of dissolved inorganic carbon (δ13CDIC). Living specimens of the planktic foraminifer species Globigerina bulloides and Globigerinoides ruber, were collected using depth stratified plankton tows during the SW monsoon upwelling period in August 1992 and the NE monsoon non-upwelling period in March 1993. We compare their distribution and the stable isotope composition to the seawater properties of the two contrasting monsoon seasons. The oxygen isotope composition of the shells (δ18Oshell) and vertical shell concentration profiles indicate that the depth habitat for both species is shallower during upwelling (SW monsoon period) than during non-upwelling (NE monsoon period). The calcification temperatures suggest that most of the calcite is precipitated at a depth level just below the deep chlorophyll maximum (DCM), however above the main thermocline. Consequently, the average calcification temperature of G. ruber and G. bulloides is lower than the sea surface temperature by 1.7±0.8 and 1.3±0.9 °C, respectively. The carbon isotope composition of the shells (δ13Cshell) of both species differs from the in situ δ13CDIC found at the calcification depths of the specimens. The observed offset between the δ13Cshell and the ambient δ13CDIC results from (1) metabolic/ontogenetic effects, (2) the carbonate chemistry of the seawater and, for symbiotic G. ruber, (3) the possible effect of symbionts or symbiont activity. Ontogenetic effects produce size trends in Δδ13Cshell–DIC and Δδ18Oshell–w: large shells of G. bulloides (250–355μm) are 0.33‰ (δ13C) and 0.23‰ (δ18O) higher compared to smaller ones (150–250 μm). For G. ruber, this is 0.39‰ (δ13C) and 0.17‰ (δ18O). Our field study shows that the δ13Cshell decreases as a result of lower δ13CDIC values in upwelled waters, while the effects of the carbonate system and/or temperature act in an opposite direction and increase the δ13Cshell as a result lower [CO32−] (or pH) values and/or lower temperature. The Δδ13Cshell–DIC [CO32−] slopes from our field data are close to those reported literature from laboratory culture experiments. Since seawater carbonate chemistry affects the δ13Cshell in an opposite sense, and often with a larger magnitude, than the change related to productivity (i.e. δ13CDIC), higher δ13Cshell values may be expected during periods of upwelling. 相似文献
12.
R. P. Kane 《Solar physics》2007,246(2):471-485
Many methods of predictions of sunspot maximum number use data before or at the preceding sunspot minimum to correlate with
the following sunspot maximum of the same cycle, which occurs a few years later. Kane and Trivedi (Solar Phys. 68, 135, 1980) found that correlations of R
z(max) (the maximum in the 12-month running means of sunspot number R
z) with R
z(min) (the minimum in the 12-month running means of sunspot number R
z) in the solar latitude belt 20° – 40°, particularly in the southern hemisphere, exceeded 0.6 and was still higher (0.86)
for the narrower belt > 30° S. Recently, Javaraiah (Mon. Not. Roy. Astron. Soc.
377, L34, 2007) studied the relationship of sunspot areas at different solar latitudes and reported correlations 0.95 – 0.97 between minima and maxima of sunspot areas at low latitudes
and sunspot maxima of the next cycle, and predictions could be made with an antecedence of more than 11 years. For the present
study, we selected another parameter, namely, SGN, the sunspot group number (irrespective of their areas) and found that SGN(min) during a sunspot minimum year at latitudes > 30° S had a correlation
+0.78±0.11 with the sunspot number R
z(max) of the same cycle. Also, the SGN during a sunspot minimum year in the latitude belt (10° – 30° N) had a correlation +0.87±0.07 with the
sunspot number R
z(max) of the next cycle. We obtain an appropriate regression equation, from which our prediction for the coming cycle 24 is R
z(max )=129.7±16.3. 相似文献
13.
We present an analysis of the evolution of the thermal flare plasma during the 14 July 2000, 10 UT, Bastille Day flare event,
using spacecraft data from Yohkoh/HXT, Yohkoh/SXT, GOES, and TRACE. The spatial structure of this double-ribbon flare consists of a curved arcade with some 100 post-flare
loops which brighten up in a sequential manner from highly-sheared low-lying to less-sheared higher-lying bipolar loops. We
reconstruct an instrument-combined, average differential emission measure distribution dEM(T)/dT that ranges from T=1 MK to 40 MK and peaks at T
0=10.9 MK. We find that the time profiles of the different instrument fluxes peak sequentially over 7 minutes with decreasing
temperatures from T≈30 MK to 1 MK, indicating the systematic cooling of the flare plasma. From these temperature-dependent relative peak times
t
peak(T) we reconstruct the average plasma cooling function T(t) for loops observed near the flare peak time, and find that their temperature decrease is initially controlled by conductive
cooling during the first 188 s, T(t)∼[1+(t/τcond)]−2/7, and then by radiative cooling during the next 592 s, T(t)∼[1−(t/τrad)]3/5. From the radiative cooling phase we infer an average electron density of n
e=4.2×1011 cm−3, which implies a filling factor near 100% for the brightest observed 23 loops with diameters of ∼1.8 Mm that appear simultaneously
over the flare peak time and are fully resolved with TRACE. We reproduce the time delays and fluxes of the observed time profiles
near the flare peak self-consistently with a forward-fitting method of a fully analytical model. The total integrated thermal
energy of this flare amounts to E
thermal=2.6×1031 erg.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014257826116 相似文献
14.
U. de Angelis L. De Cesare A. Forlani G. Platania 《Astrophysics and Space Science》1974,27(1):117-135
The consequences of gas-liquid phase transitions in the core of hot white dwarf stars are discussed. Expressions for the latent heat and the liquefaction curveT
l
=T
l
(Q) are obtained. Then amodel for a hot white dwarf is introduced and the corresponding liquefaction sequences are built on the H-R diagram; relations luminosity-central temperature and effective temperature-central temperature are also given for liquefying white dwarfs.Finally the cooling curves are obtained for such stars taking into account the effect of latent heat emission.Our results seem to suggest a possible identification of the central stars of planetary nebulae as hot liquefying white dwarfs. 相似文献
15.
V. S. Troitskii I. V. Gorbacheva G. L. Suchkin L. N. Bondar 《Astrophysics and Space Science》1992,190(1):9-22
It is shown that the Hubble curvem(z) for galaxies and quasars averaged over a large volume of data forms in the first approximation a single continuous curve in the interval of red shifts 10–2.5z4.5, which is satisfactorily described by the dependence
.A large deviation of the observed mean dependence from the theoretical one predicted by the standard cosmology is explained by the evolution of the galaxy and especially quasar luminosity. The corresponding mid-statistical function of the absolute luminosity variation for the last 4/5 times of existence in the Universe is equal toM(z)–M(z
0)=logz/z
0+2z–0.4z
2.The luminosity of the most far distant from the observed quasars on the average by 5–6 stellar magnitudes high than the luminosity of near galaxies and quasars. It is obtained that even the most far distant quasars atz5 are in the maximum of luminosity, or their extinction has just began, thus the quasar formation should be expected forz>(5–6). The relative rate of the luminosity decrease of galaxies and near quasars is rather accurately amounts in the recent epoch 7% per 109 years. The obtained average Hubble curve of galaxies and quasars is evidently the main cause of their evolution in the Universe. 相似文献
16.
Various methods are explored for obtaining regularized solutions of the severely ill-posed Laplace inversion problem involved in deriving plasma temperature (T) structure (differential emission measure(T)) from bremsstrahlung spectra. Inversions of simulated data show that zero-order regularisation (Tikhonov regularisation inL
2 space) is very unsatisfactory even with weighting, while first-order regularisation (Tikhonov regularisation in Sobolev space) yields reasonable results.The method is applied to a high-resolution hard X-ray flare spectrum observed by Lin and Schwartz (1987) and yields a positive solution for(T) showing that a purely thermal interpretation is possible for that event. The form of(T) found has two broad features: one peaking at around 107 K and falling off steeply toward 2 × 108 K; a second spread around a peak near 4.5 × 108 K. The interpretation of such(T) in terms of plasma heating and conductive flux is discussed in terms of plasma heat fluxes and heating rates. For 1-D geometry, the distribution of the plasma heating rateH(T) per unit volume is inferred from(T) in the limits of classical diffusive conduction and of saturated heat flux, the former being relevant atT below around 5 × 107 K and the latter at much higherT. We find there exists a maximum inH(T) around 2 × 108 K, a fact which may be important for energy release theories. 相似文献
17.
The electron collision excitation rates recently calculated for transitions in Si xiii by Keenan et al. (1987) are used to derive the electron temperature sensitive ratio G(=(f + i)/r and the density sensitive ratio R(=f/i), where i, f, and r are the intercombination (1s
2
1
S – 1s2p
3
P
1, 2) forbidden (1s
2
1
S – 1s2s
3
S), and resonance (1s
2
1
S – 1s2p
1
P), transitions respectively. Also estimated are the values of R in the low-density limit (R
0) as a function of electron temperature. The theoretical G ratio at the temperature of maximum emissivity for Si xiii, G(T
m) = 0.70, is in much better agreement with the observed G for the 1985, May 5 flare determined by McKenzie et al. (G = 0.60 ± 0.07) than is the earlier calculation of Pradhan, who derived G(T
m) = 0.85. The error in the observed R
0 ratio is so large that both our result and Pradhan's fall within the acceptable limits of uncertainty and hence one cannot estimate which of the two is the more accurate. 相似文献
18.
J.L. McLain 《Planetary and Space Science》2009,57(13):1642-39
A study has been made using a variable temperature flowing afterglow Langmuir probe technique (VT-FALP) to determine the equilibrium temperature dependencies of the dissociative electron-ion recombination of the protonated cyanide ions (RCNH+, where R=H, CH3 and C2H5) and their symmetrical proton-bound dimers (RCNH+NCR). The power law temperature dependencies of the recombination coefficients, αe, over the temperature range 180 to 600 K for the protonated ions are αe(T)(cm3 s−1)=3.5±0.5×10−7 (300/T)1.38 for HCNH+, αe(T)=3.4±0.5×10−7 (300/T)1.03 for CH3CNH+, and αe(T)=4.6±0.7×10−7 (300/T)0.81 for CH3CH2CNH+. The equivalent values for the proton-bound dimers are αe(T)(cm3 s−1)=2.4±0.4×10−6(300/T)0.5 for (HCN)2H+ to αe(T)=2.8±0.4×10−6(300/T)0.5 for (CH3CN)2H+, and αe(T)=2.3±0.3×10−6(300/T)0.5 for (CH3CH2CN)2H+. The relevance of these data to molecular synthesis in the interstellar medium and the Titan ionosphere are discussed. 相似文献
19.
D.V. Erofeev 《Solar physics》2001,198(1):31-50
To investigate the relationship between solar activity and the large-scale axisymmetric magnetic field of the Sun, we inferred from sunspot data over the period 1964–1985 a latitude–time distribution of magnetic field associated with active regions. This has been done allowing for both bipolar structure of the active regions and inclination of their axes to parallels of latitude, so the inferred magnetic field characterizes latitudinal separation of magnetic polarities which might be related to the large-scale magnetic field of the Sun according to the Babcock–Leighton model. The inferred magnetic field, A
z, is compared with the longitude-averaged (zonal) magnetic field of the Sun, B
z, derived from series of magnetograms obtained at Mount Wilson Observatory in the years 1964–1976, and at Kitt Peak National Observatory during the period from 1976 to 1985. The inferred magnetic field, A
z, exhibits a complex structure distribution of magnetic polarities with respect to latitude and time. Apart from concentration of the different polarity magnetic fields inside the high- and low-latitude portions of the sunspot belts, bipolar active regions produce an intensive, shorter-scale component of the magnetic field which varies on the time scale of about 2 years. Such a short-term variation of A
z reveals substantial correlation with the short-term component of B
z which has the form of the poleward-drifting streams of magnetic field. Most significant correlation takes place between the short-term variations of A
z occurring at latitudes below 20° and those of the large-scale magnetic fields occurring at middle latitudes of 40–50°. Moreover we analyze harmonic coefficients a
l and b
l obtained by expanding A
z and B
z into series in terms of the spherical harmonics. Power spectra of the time-dependent harmonic coefficients indicate that both A
z and B
z reveal a number of resonant modes which oscillate either with the 22-year period in the case of the anti-symmetric (odd-l) modes or with periods of about 2 years in the case of the symmetric (even-l) modes, but the resonant modes of A
z have significantly larger values of the spherical harmonic degree l (and, hence, smaller spatial scales) as compared to those of B
z. It is found that there is a close relationship between the harmonic coefficients b
l and a
m for which either m–l16 (even l=4,...,10) or m–l=4 (odd l=5,...,15). 相似文献
20.
Recent observations with EUV imaging instruments such as SOHO/EIT and TRACE have shown evidence for flare-like processes at
the bottom end of the energy scale, in the range of E
th≈1024–1027 erg. Here we compare these EUV nanoflares with soft X-ray microflares and hard X-ray flares across the entire energy range.
From the observations we establish empirical scaling laws for the flare loop length, L(T)∼T, the electron density, n
e(T)∼T
2, from which we derive scaling laws for the loop pressure, p(T)∼T
3, and the thermal energy, E
th∼T
6. Extrapolating these scaling laws into the picoflare regime we find that the pressure conditions in the chromosphere constrain a height level for flare loop footpoints, which scales
with h
eq(T)∼T
−0.5. Based on this chromospheric pressure limit we predict a lower cutoff of flare loop sizes at L
∖min≲5 Mm and flare energies E
∖min≲1024 erg. We show evidence for such a rollover in the flare energy size distribution from recent TRACE EUV data. Based on this
energy cutoff imposed by the chromospheric boundary condition we find that the energy content of the heated plasma observed
in EUV, SXR, and HXR flares is insufficient (by 2–3 orders of magnitude) to account for coronal heating. 相似文献