3,406 research outputs found
The height dependence of temperature - velocity correlation in the solar photosphere
We derive correlation coefficients between temperature and line-of-sight
velocity as a function of optical depth throughout the solar photosphere for
the non-magnetic photosphere and a small area of enhanced magnetic activity.
The maximum anticorrelation of about -0.6 between temperature and line-of-sight
velocity in the non-magnetic photosphere occurs at log tau5 = -0.4. The
magnetic field is another decorrelating factor along with 5-min oscillations
and seeing.Comment: In press,"Modern Solar Facilities - Advanced Solar Science",
(Gottingen), Universitatsverlag Gottingen, 139-142, 200
Boltzmann theory of engineered anisotropic magnetoresistance in (Ga,Mn)As
We report on a theoretical study of dc transport coefficients in (Ga,Mn)As
diluted magnetic semiconductor ferromagnets that accounts for quasiparticle
scattering from ionized Mn acceptors with a local moment and
from non-magnetic compensating defects. In metallic samples Boltzmann transport
theory with Golden rule scattering rates accounts for the principle trends of
the measured difference between resistances for magnetizations parallel and
perpendicular to the current. We predict that the sign and magnitude of the
anisotropic magnetoresistance can be changed by strain engineering or by
altering chemical composition.Comment: 4 pages, 2 figure
Magnetic loop emergence within a granule
We investigate the temporal evolution of magnetic flux emerging within a
granule in the quiet-Sun internetwork at disk center. We combined IR
spectropolarimetry performed in two Fe I lines at 1565 nm with
speckle-reconstructed G-band imaging. We determined the magnetic field
parameters by a LTE inversion of the full Stokes vector using the SIR code, and
followed their evolution in time. To interpret the observations, we created a
geometrical model of a rising loop in 3D. The relevant parameters of the loop
were matched to the observations where possible. We then synthesized spectra
from the 3D model for a comparison to the observations. We found signatures of
magnetic flux emergence within a growing granule. In the early phases, a
horizontal magnetic field with a distinct linear polarization signal dominated
the emerging flux. Later on, two patches of opposite circular polarization
signal appeared symmetrically on either side of the linear polarization patch,
indicating a small loop-like structure. The mean magnetic flux density of this
loop was roughly 450 G, with a total magnetic flux of around 3x10^17 Mx. During
the ~12 min episode of loop occurrence, the spatial extent of the loop
increased from about 1 to 2 arcsec. The middle part of the appearing feature
was blueshifted during its occurrence, supporting the scenario of an emerging
loop. The temporal evolution of the observed spectra is reproduced to first
order by the spectra derived from the geometrical model. The observed event can
be explained as a case of flux emergence in the shape of a small-scale loop.Comment: 10 pages, 13 figures; accepted for Astronomy and Astrophysics; ps and
eps figures in full resolution are available at
http://www.astro.sk/~koza/figures/aa2009_loop
Calcification depth of deep-dwelling planktonic foraminifera from the eastern North Atlantic constrained by stable oxygen isotope ratios of shells from stratified plankton tows
Stable oxygen isotopes (delta O-18) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the delta O-18 of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies delta O-18 differences and can thus potentially provide information on the vertical structure of the water column. However, to fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context since their calcification depth reaches below the surface mixed layer. Here we report delta O-18 measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the eastern North Atlantic. Size and crust effects on the delta O-18 signal were evaluated showing that a larger size increases the delta O-18 of G. inflata and G. hirsuta, and a crust effect is reflected in a higher delta O-18 signal in G. truncatulinoides. The great majority of the delta O-18 values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300m for G. inflata and to about 500m for G. hirsuta. In G. scitula, despite a strong subsurface maximum in abundance, the vertical delta O-18 profile is flat and appears dominated by a surface layer signal. In G. truncatulinoides, the delta O-18 profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The delta O-18 values are more consistent with the predictions of the Shackleton (1974) palaeotemperature equation, except in G. scitula which shows values more consistent with the Kim and O'Neil (1997) prediction. In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.Agência financiadora Portuguese Foundation for Science and Technology (FCT): SFRH/BD/78016/2011;
UID/Multi/04326/2019
European Union Seventh Framework Programme (FP7/2007-2013): 228344-EUROFLEETS
German Research Foundation (DFG): WA2175/2-1; WA2175/4-1
German Climate Modelling consortium PalMod - German Federal Ministry of Education and Research (BMBF)info:eu-repo/semantics/publishedVersio
Observations of ozone production in a dissipating tropical convective cell during TC4
From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times (15:12–17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of 1.6–4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of (2.1–2.5)×106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (1.2, 1.0, and 1.7×106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70–97% of the O3 change occurred in 2.5–5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry
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