共查询到20条相似文献,搜索用时 31 毫秒
1.
S. Perraut A. Roux F. Darrouzet C. de Villedary M. Mogilevsky F. Lefeuvre 《Annales Geophysicae》1998,16(9):1105-1116
The IESP experiment implemented onboard the Interball auroral probe measures the six components (3B, 3E) of the waves in the ULF range: 0.1–10 Hz and from time to time 0–30 Hz. Two different kinds of waves have been observed in the auroral region at altitudes between 10 000 and 20 000 km: (1) electrostatic emissions which consist of quasi-monochromatic structures with frequencies above the oxygen gyrofrequency, superimposed on a wide band signal interpreted as a Doppler broadening, (2) electromagnetic wide band spectrum fluctuations. These emissions are interpreted as current-driven electromagnetic or electrostatic ion cyclotron waves. The electromagnetic/electrostatic character is controlled by the plasma parameter i and by the O+ concentration. 相似文献
2.
We study the changes in the rate of seismotectonic strains in the Earth’s crust in two of the most seismically active Central
Asian areas, the Garm region in Tadjikistan and the Northern Tien Shan, which are excited by high energy pulsed electromagnetic
irradiation. It is shown that in both areas the average rates of strain release increase by a factor of 10–20. The increment
of the seismotectonic strains initiated during the entire period of electromagnetic treatment is 1.3 × 10−6–6.3 × 10−6, which is comparable with the value of crustal strains observed during the preparation of strong earthquakes and amounts
to 3–13% of the ultimate strains for rocks. Such a contribution to the process of quasi-plastic strains of the crust results
in the additional relaxation of elastic stresses by 0.4–1.67 bar, which corresponds to approximately 1–17% of the stress released
in the sources of strong earthquakes. The spatial variations in the changes of the strain rate during electromagnetic treatment
are studied, and their correlation with the level of stresses in the Earth’s crust is revealed. It is shown that the change
in the strain rate during the electromagnetic excitation can be used as the criterion for active monitoring of the stress
state of the medium for the purposes of predicting the location, time, and magnitude of strong earthquakes. 相似文献
3.
Yun-Lin Zhang Hai-Jing An Xiao-Ling Liu Yu-Lan Si Mei Jiang Wu-Si Zhang 《地震学报(英文版)》1993,6(3):675-683
The high accuracy, automatic, digital MT measurement system with five electromagnetic components was firstly adopted by the
author to the section MT monitor and measurement in the middle Qilian mountain in the Northwestern China, the more real precursory
information of impending earthquake electromagnetic rediation of GongheM=7.0 earthquake (April, 1990) in Qinghai province was obtained by the system.
The new complete quantification frequency analysis was firstly used in this paper in both time and space domains for the analysis
of repeated measurement data at all sites.
This paper concludes the precursory spectral characteristics of electromagnetic radiation before strong earthquake as following:
1. The spectra appears as the synchronous electric field interference type mainly of conduction current; 2. Narrow band (0.5
– 20s) of spectral period; 3. The singularity of amplitude (the pulse amplitudes of interference electric field is 102 times the normal values); 4. They show the directionality of preparing focus to some extent; 5. The intermittent of radiation
(three peak periods appeared three days before the main shock). It is more significant that there existed a relative quiet
period of about 48 hours between the peak period and the occurrence, observators can response quickly at observational sites
and take it as one of the observational criterions for impending prediction.
This paper also points out that the impending earthquake electromagnetic radiation obtained by the MT measurement system is
mainly the conduction current, and the high-conductive layer existed commonly in the crust may serve as the better paths for
the conduction current circuit and enables the far away MT measurement sites to receive it.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 186–193, 1993. 相似文献
4.
The portable highly sensitive measuring station KVVN-7 has been designed. It enables us to perform frequency sounding with
controllable sources and audio-magnetotelluric sounding in the field of natural variations in an electromagnetic field within
one session. Signal recording is made by seven channels (three magnetic and four electric ones) in a broad frequency spectrum
(0.1–2000 Hz) with elimination of frequencies on the edges of the set frequency range and in the odd harmonics of industrial
frequency (up to the ninth harmonic). The station incorporates the system of band-stop filters and anti-alias filters at resistors
having a low temperature coefficient of resistance (TCR is lower than 25 × 10−6 °C−1) and capacitors having a low temperature coefficient of capacity (TCC is lower than ±30 × 10−6 °C−1). Application of the KVVN-7 station allows the electric conductivity and fluid regime of the upper crust to be studied for
both implementation of geological tasks and tasks related to electromagnetic monitoring of seismoactive zones in combination
with seismic methods. The example of practical application of the KVVN-7 station in the Lovozero-Pulozero profile (Kola Peninsula)
has been presented. A high effectiveness of a station has been demonstrated when study of a fluid-saturated layer with conductivity
of a dilatancy-diffuse origin (“DD layer”) in the upper crust. The further perfection of the KVVN-7 measuring station is aimed
at the design of a completely automated recording system through data recording to a built-in data medium (flash memory).
Additionally, it is suggested to use a built-in analog-to-digital converter of high resolution (24 bit) for every channel
in order to broaden the dynamical range of the station. 相似文献
5.
Small-scale (scales of ∼0.5–256 km) electric fields in the polar cap ionosphere are studied on the basis of measurements of
the Dynamics Explorer 2 (DE-2) low-altitude satellite with a polar orbit. Nineteen DE-2 passes through the high-latitude ionosphere
from the morning side to the evening side are considered when the IMF z component was southward. A rather extensive polar cap, which could be identified using the ɛ-t spectrograms of precipitating particles with auroral energies, was formed during the analyzed events. It is shown that the
logarithmic diagrams (LDs), constructed using the discrete wavelet transform of electric fields in the polar cap, are power
law (μ ∼ s
α). Here, μ is the variance of the detail coefficients of the signal discrete wavelet transform, s is the wavelet scale, and index α characterizes the LD slope. The probability density functions P(δE, s) of the electric field fluctuations δE observed on different scales s are non-Gaussian and have intensified wings. When the probability density functions are renormalized, that is constructed
of δE/s
γ, where γ is the scaling exponent, they lie near a single curve, which indicates that the studied fields are statistically
self-similar. In spite of the fact that the amplitude of electric fluctuations in the polar cap is much smaller than in the
auroral zone, the quantitative characteristics of field scaling in the two regions are similar. Two possible causes of the
observed turbulent structure of the electric field in the polar cap are considered: (1) the structure is transferred from
the solar wind, which is known to have turbulent properties, and (2) the structure is generated by convection velocity shears
in the region of open magnetic field lines. The detected dependence of the characteristic distribution of turbulent electric
fields over the polar cap region on IMF B
y
and the correlation of the rms amplitudes of δE fluctuations with IMF B
z
and the solar wind transfer function (B
y
2 + B
z
2)1/2sin(θ/2), where θ is the angle between the geomagnetic field and IMF reconnecting on the dayside magnetopause when IMF B
z
< 0, together with the absence of dependence on the IMF variability are arguments for the second mechanism. 相似文献
6.
John E. Bailey Andrew J. L. Harris Jonathan Dehn Sonia Calvari Scott K. Rowland 《Bulletin of Volcanology》2006,68(6):497-515
An open channel lava flow on Mt. Etna (Sicily) was observed during May 30–31, 2001. Data collected using a forward looking
infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermometer showed that the bulk volume flux
of lava flowing in the channel varied greatly over time. Cyclic changes in the channel's volumetric flow rate occurred over
several hours, with cycle durations of 113–190 min, and discharges peaking at 0.7 m3 s−1 and waning to 0.1 m3 s−1. Each cycle was characterized by a relatively short, high-volume flux phase during which a pulse of lava, with a well-defined
flow front, would propagate down-channel, followed by a period of waning flow during which volume flux lowered. Pulses involved
lava moving at relatively high velocities (up to 0.29 m s−1) and were related to some change in the flow conditions occurring up-channel, possibly at the vent. They implied either a
change in the dense rock effusion rate at the source vent and/or cyclic-variation in the vesicle content of the lava changing
its bulk volume flux. Pulses would generally overspill the channel to emplace pāhoehoe overflows. During periods of waning
flow, velocities fell to 0.05 m s–1. Blockages forming during such phases caused lava to back up. Occasionally backup resulted in overflows of slow moving ‘a‘ā
that would advance a few tens of meters down the levee flank. Compound levees were thus a symptom of unsteady flow, where
overflow levees were emplaced as relatively fast moving pāhoehoe sheets during pulses, and as slow-moving ‘a‘ā units during
backup. Small, localized fluctuations in channel volume flux also occurred on timescales of minutes. Volumes of lava backed
up behind blockages that formed at constrictions in the channel. Blockage collapse and/or enhanced flow under/around the blockage
would then feed short-lived, wave-like, down-channel surges. Real fluctuations in channel volume flux, due to pulses and surges,
can lead to significant errors in effusion rate calculations.
Editorial responsibility: A. Woods 相似文献
7.
We present a preliminary study of the dependence of the statistical features of the soil motion due to seismic noise on the
near-surface geology in the frequency range from 1 Hz to ∼ 40 Hz. In detail, we have investigated the 3D average squared soil
displacement 〈r2〉 and the distribution function of the displacement flctuations at different geological sites. The anomalous scaling of the
average squared soil displacement 〈r2(τ)〉~τα, and the Gaussian shape of the probability distribution function of its fluctuations suggest that the soil motion under the
influence of the seismic noise is consistent with a persistent fractional Brownian motion (fBm) characterized by a scaling
exponent 1.5 < α < 2. Therefore, the seismic noise-field, thought as a stochastic process, shows a markovian character with
a memory longer than a pure Brownian motion (α = 1/2). Moreover, a dependence of such persistent behavior of the noise-field
dynamics on the near-surface local geology has been found and it is discussed. 相似文献
8.
Scaling properties of variable electric fields in the topside ionosphere have been investigated on scales s from ∼30 m to 2 km by FAST electric field observations with sample rate of 512 s−1, in sixteen events of the broadband ELF turbulence. It is shown that down to scales of a few hundred meters, the power of turbulent electric fluctuations is a power law, ∼s α. Scaling index α derived from the slope of logarithmic diagrams (LD) constructed by the discrete wavelet transform of data can be estimated as α = 2.2 ± 0.3, which is close to α estimate earlier reported for scales 1–30 km by electric field observations of the Dynamics Explorer 2 satellite. The behavior of α index is analyzed near the scale of the order of electron inertial length λe = c/ω0 (ω0 being the electron plasma frequency). At altitudes considered (700–2500 km), λe makes 100–900 m. We demonstrate that at scales ≤λe, a decrease of LD slope and deviation from the power law are typically observed. As pointed out in the discussion, this feature cannot be identified as a transition to the diffusion range, where dissipation of the turbulence occurs. 相似文献
9.
A. V. Petlenko Yu. A. Kopytenko V. A. Martines V. A. Pilipenko V. S. Ismagilov 《Geomagnetism and Aeronomy》2011,51(5):584-598
An analysis of the BEAR experiment and Polar satellite data showed that several ionospheric sources could act almost simultaneously
in the area of Pi2-type geomagnetic pulsations. The aim of this study is to locate these sources and determine their coherence
in the narrow-frequency band of (6–10) × 10−3 Hz. By using gradient analysis methods, we revealed the local sources of oscillations coherent (phased), that allows one
to treat their contributions as manifestations of the fine structure of the field of Pi2 pulsations. 相似文献
10.
The results from Raman spectroscopy analysis of salt aqueous solutions at −170°C demonstrate that for those clearly sharp
iron peaks whose Raman wavenumber is close to each other such as NO
3
−
and CO
3
2−
, their original shape could be restorable by the stripping technique, and that ice’s sharp characteristic peak 3090–3109
cm−1) is steady, while the spectrum band of the complex compound (nCl−-[H+-OH−]n) chlorine ion combined chemically with water molecule is 3401–3413 cm−1. On the other hand, the research shows that the higher the negative iron concentration, the stronger its Raman characteristic
peak intensity and the smaller the ice’s. Based on the number of data and theoretical work, the strong correlation of the
molar concentration of negative ion with the S
i/S
H
2O band area ratio is built up. Moreover, the developed Raman method is successfully used in the component analysis of the
field fluid inclusions from Silurian sandstone in Tarim basin. 相似文献
11.
Gianfranco Di Vincenzo Laura Bracciali Paola Del Carlo Kurt Panter Sergio Rocchi 《Bulletin of Volcanology》2010,72(4):487-505
The AND-2A drillcore (Antarctic Drilling Program—ANDRILL) was successfully completed in late 2007 on the Antarctic continental
margin (Southern McMurdo Sound, Ross Sea) with the aim of tracking ice proximal to shallow marine environmental fluctuations
and to document the 20-Ma evolution of the Erebus Volcanic Province. Lava clasts and tephra layers from the AND-2A drillcore
were investigated from a petrographic and stratigraphic point of view and analyzed by the 40Ar–39Ar laser technique in order to constrain the age model of the core and to gain information on the style and nature of sediment
deposition in the Victoria Land Basin since Early Miocene. Ten out of 17 samples yielded statistically robust 40Ar–39Ar ages, indicating that the AND-2A drillcore recovered ≤230 m of Middle Miocene (∼128–358 m below sea floor, ∼11.5–16.0 Ma)
and >780 m of Early Miocene (∼358–1093 m below sea floor, ∼16.0–20.1 Ma). Results also highlight a nearly continuous stratigraphic
record from at least 358 m below sea floor down hole, characterized by a mean sedimentation rate of ∼19 cm/ka, possible oscillations
of no more than a few hundreds of ka and a break within ∼17.5–18.1 Ma. Comparison with available data from volcanic deposits
on land, suggests that volcanic rocks within the AND-2A core were supplied from the south, possibly with source areas closer
to the drill site for the upper core levels, and from 358 m below sea floor down hole, with the “proto-Mount Morning” as the
main source. 相似文献
12.
M. G. Deminov G. F. Deminova G. A. Zherebtsov O. M. Pirog N. M. Polekh 《Geomagnetism and Aeronomy》2011,51(3):348-355
Results of statistical analysis of the properties of variability of F2-layer maximum parameters (critical frequency foF2 and the height hmF2) in quiet midlatitude ionosphere under low solar activity in the daytime (1000–1500 LT) and nighttime (2200–0300 LT) hours
are presented on the basis of Irkutsk station data for 2007–2008. It is found that the distribution density of δfoF2 could be presented as consisting of two distinctly different normal laws of this distribution, one of which corresponds
to weak (|δfoF2| < 10%) fluctuations in foF2 and the other corresponds to strong (30% > |δfoF2| > 10%) fluctuations. Weak fluctuations in foF2 to a substantial degree are related to ionospheric variability at times less of than 1–3 h and determine the δfoF2 variability in the daytime hours. Strong fluctuations in foF2 are mainly related to day-to-day variability of the ionosphere at a fixed local time, the variability increasing by approximately
a factor of 3 during the transition from day to night and determining the δfoF2 variability in the nighttime hours. The distribution density of ΔhmF2 is close to the normal distribution law. An interpretation of the different character of the distribution densities of δfoF2 and ΔhmF2 is given. 相似文献
13.
ChangLiang Yin TanDong Yao LiDe Tian DongNian Liu WuSheng Yu DongMei Qu 《中国科学D辑(英文版)》2008,51(7):966-975
Oxygen stable isotope of atmospheric water vapor is widely used to study the modern process of climate. Atmospheric water
vapor samples were collected at Dlingha, northeast of Tibetan Plateau during the period from July 2005 to February 2006. The
variation of δ
18O and the relationships between δ
18O and both the temperature and specific humidity are analyzed in this paper. Results show that the seasonal variation of δ
18O of atmospheric water vapor at Delingha is remarkable with higher δ
18O in summer and lower δ
18O in winter. The temporal variation of vapor δ
18O shows obvious fluctuations, with magnitude of over 37‰ The daily variation of the δ
18O is highly correlated with air temperature. The relationship between δ
18O and atmospheric water vapor content is complex. Study shows that δ
18O of atmospheric water vapor is positively correlated with specific humidity in winter in seasonal scale and inversely correlated
with specific humidity in summer rainy period. The δ
18O values of atmospheric water vapor are lower than those of precipitation at Delingha, and the average difference is 10.7‰
Variations of δ
18O of atmospheric water vapor is also found to be affected by precipitation events, The model results show that the precipitation
effect could have caused the vapor δ
18O in the raining season to lower by 7% in average in July and August.
Supported by the National Natural Science Foundation of China (Grant Nos. 40671043, 40571039 and 40771048) and National Basic
Research Program of China (Grant No. 2005CB422002) 相似文献
14.
A. I. Boldyrev A. E. Vyazilov V. N. Ivanov R. V. Kemaev V. Ya. Korovin A. V. Melyashinskii K. V. Pamukhin V. N. Panov Yu. N. Shvyrev 《Geomagnetism and Aeronomy》2016,56(4):503-512
Measurements of the atmospheric electric field strength made by an electrostatic fluxmeter with a unique threshold sensitivity for such devices (6 × 10–2–10–3 V m–1 Hz–1/2 in the 10–3–25 Hz frequency range) and wide dynamic (120 dB) and spectral (0–25 Hz) ranges, are presented. The device parameters make it possible to observe the electric component of global electromagnetic Schumann resonances and long-period fluctuations in the atmospheric electric field strength. 相似文献
15.
During the spring seasons of 1983, 1986 and 1987 the development of phytoplankton in Lake Zürich was investigated (from February
to May) using samples taken at short term intervals. The aim was to describe the effects of the short term dynamics of environmental
factors on the algal growth. The results could then be used to discuss the existing theories to assess the start of phytoplankton
growth pulses in spring.
Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first growth pulse, despite of
a still very unstable water column (sometimes inverse thermal stratification). Mainly flagellates andStephanodiscus hantzschii increased their biomass and achieved net growth rates of 0.1 and up to 0.65 d−1 respectively. During such a phase the mixing depth was always smaller than the euphotic depth. Later on, at the start of
the spring bloom (=last growth pulse in spring before the clear water stage), the intensity of vertical mixing as well as
the mixing depth were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated (contribution
up to 75.5% of the areal biomass reaching 60 g fresh weight m−2) and the growth rate rose to a maximum of 0.65 d−1.
Standard models of critical depth considers that there is only a biomass increase if the mixing depth is smaller than the
depth of a water layer positive balanced between production and respiration. This model for determining the beginning of a
phytoplankton growth pulse in spring takes no account of the favorable light conditions for phytoplankton cells at calm and
sunny days in February and March. The newly developed threshold value model takes these situations into account: It assumes
that the phytoplankton biomass increases when the calculated effective light climate is equal or greater than a previously
fixed threshold. The calculations are based on the mean light intensity within the mixed layer at windy days or within the
euphotic depth (z
eu) at calm days. In Lake Zürich a minimum of 0.2 106 J m−2d−1 (=0.9 mol quanta m−2d−1) has to be reached or surpassed in at least 3 days before an exponential increase of algal biomass can occur. The value does
not depend on short term fluctuations in neither radiation nor mixing depth. It seems that this value is rather low comparing
with those of investigations in other water bodies (up to 0.8 106 J m−2 d−1) but high related to values from algal cultures (0.02 106 J m−2d−1). As the weather can only be forecasted a few days ahead with any certainty the period for a more or less accurate prediction
of an algal bloom is restricted to about 1 to 5 days. 相似文献
16.
Seismic wave field fluctuations below Lanzhou Comprehensive Test Ban Treaty Organization seismic array are determined and
interpreted to describe the scattering characteristics of the crust beneath the northeastern margin of Qinghai–Tibet plateau
in China. The frequency-dependent intensities of the mean and fluctuation wave fields are analyzed for 21 deep (206–632 km
depth) teleseismic events. The observed wave field fluctuations in the frequency range 0.5–2.5 Hz can be explained by the
scattering of the teleseismic P wave front at random media-type structures. The stable and narrow range of the fluctuation
parameters from these teleseismic events indicates evidence for scattered seismic phases which are generated inside the crust.
The reasonable structural models contain heterogeneities with 1–3% velocity fluctuations and 2.4–8.2 km correlation lengths
in the crust with 53 km thickness. 相似文献
17.
Climatic variations in the past 140 ka recorded in core RM, east Qinghai-Xizang Plateau 总被引:6,自引:0,他引:6
The sequences of climatic evolution are reconstructed by the analyses of δ13C and δ18O of carbonate from core RM in the Zoige Basin since 140 kaB. P. During the Last Glaciation there existed at least seven warm
climatic fluctuations and five cold events correlated with the records of ice core and deep sea, and during the preceding
last interglacial period there were two cold climatic variations coinciding with the record of ice core GRIP. These results
de-pict climatic instability in east Qinghai-Xizang Plateau over the last interglacial period. In addition, the environmental
proxies of the carbonate content and pigments indicate the similar results to the stable isotope record from core RM.
Project supported by the Chinese Climbing Project (85-029-02-01). 相似文献
18.
Corrado Cigolini 《Bulletin of Volcanology》2010,72(6):693-704
Data collected at Somma-Vesuvius during the 1998–1999 radon surveys have been revisited and reinterpreted in light of recent
geophysical and geochemical information. The duration of selected radon anomalies, together with the decay properties of radon,
have been used to estimate the permeability and porosity of rocks of the deep hydrothermal system. The current local cyclic
seismicity is explained by means of a double convective-cell model. Convective cells are separated by a low-permeability horizon
located at about 2–2.5 km below sea level. Fluids convecting within the upper cells show temperatures ranging 300–350°C. Rock
permeabilities in this sector are estimated on the order of 10−12 m2, for porosities (ϕ) of about 10−5 typical of a brittle environment where fluid velocities may reach ∼800 m/day. Fluid temperatures within the lower cells may
be as high as 400–450°C, consistent with supercritical regimes. The hydrodynamic parameters for these cells are lower, with
permeability k ∼ 10−15 m2, and porosity ranging from 10−6 to 10−7. Here, fluid motion toward the surface is controlled by the fracture network within a porous medium approaching brittle–ductile
behaviour, and fluid velocities may reach ∼1,800 m/day. The low-permeability horizon is a layer where upper and lower convecting
cells converge. In this region, fluids (convecting both at upper and lower levels) percolate through the wallrock and release
their brines. Due to self-sealing processes, permeability within this horizon reaches critical values to keep the fluid pressure
near lithostatic pressure (for k ∼ 10−18 m2). Deep fluid pressure buildups precede the onset of hydrothermally induced earthquakes. Permeability distribution and rock
strength do not exclude that the next eruption at Somma-Vesuvius could be preceded by a seismic crisis, eventually leading
to a precursory phreatic explosion. The coupling of these mechanisms has the potential of inducing pervasive failure within
rocks of the hydrothermal shell, and may be a prelude to a magmatic eruption. It is finally emphasised that the integrated
analysis of seismic and geochemical data, including radon emissions, could be successfully used in testing temperature distributions
and variations of porosity and permeability in active geothermal reservoirs. 相似文献
19.
FANG JingYun LIU GuoHua ZHU Biao WANG XiaoKe & LIU ShaoHui Department of Ecology College of Environmental Sciences and Key Laboratory for Earth Surface Processes of the Ministry of Education Peking University Beijing China Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2007,50(1):92-101
There is a general agreement that forest ecosystems in the Northern Hemisphere function as signifi-cant sinks for atmospheric CO2; however, their magnitude and distribution remain large uncertainties. In this paper, we report the carbon (C) stock and its change of vegetation, forest floor detritus, and mineral soil, annual net biomass increment and litterfall production, and respiration of vegetation and soils between 1992 to 1994, for three temperate forest ecosystems, birch (Betula platyphylla) forest, oak (Quercus liaotungensis) forest and pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the C budgets of these forest ecosystems. Our results indicated that total C density (organic C per hectare) of these forests ranged from 250 to 300 t C ha-1, of which 35―54 t C ha-1 from vegetation biomass C and 209―244 t C ha-1 from soil organic C (1 m depth, including forest floor detritus). Biomass C of all three forests showed a net increase, with 1.33―3.55 t C ha-1 a-1 during the study period. Litterfall production, vegetation autotrophic respiration, and soil heterotrophic respira-tion were estimated at 1.63―2.34, 2.19―6.93, and 1.81―3.49 t C ha-1 a-1, respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t C ha-1 a-1, about half of which (46%―59%, 3.20―5.89 t C ha-1 a-1) was converted to net primary production. Our results suggested that pine forest fixed C of 4.08 t ha-1 a-1, whereas secondary forests (birch and oak forest) were nearly in balance in CO2 exchange between the atmosphere and ecosystems. 相似文献
20.
Two methods were used to quantify the flux of volcanic sulphur (as the equivalent mass of SO2) to the stratosphere over different timescales during the Holocene. A combination of satellite-based measurements of sulphur
yields from recent explosive volcanic eruptions with an appropriate rate of explosive volcanism for the past 200 years constrains
the medium-term (∼102 years) flux of volcanic sulphur to the stratosphere to be ∼1 Mt a–1, with lower and upper bounds of 0.3 and 3 Mt a–1. The short-term (∼10- to 20-year) flux due to small magnitude (1010–1012 kg) eruptions is of the order of 0.4 Mt a–1. At any time the instantaneous levels of sulphur in the stratosphere are dominated by the most recent (0–3 years) volcanic
events. The flux calculations do not attempt to address this very short timescale variability. Although there are significant
errors associated with the raw sulphur emission data on which this analysis is based, the approach presented is general and
may be readily modified as the quantity and quality of the data improve. Data from a Greenland ice core support these conclusions.
Integration of the sulphate signals from presumed volcanic sources recorded in the GISP2 core provides a minimum estimate
of the 103–year volcanic SO2 flux to the stratosphere of 0.5–1 Mt a–1 over the past 9000 years. The short-term flux calculations do not account for the impact of rare, large events. The ice-core
record does not fully account for the contribution from small, frequent events.
Received: 27 September 1995 / Accepted: 13 December 1995 相似文献