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| 2. |
- Behar, Etienne, et al.
(författare)
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Mass loading at 67P/Churyumov-Gerasimenko : A case study
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:4, s. 1411-1418
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Tidskriftsartikel (refereegranskat)abstract
- We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.
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| 3. |
- Berthelsen, A., et al.
(författare)
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Recording marine airgun shots at offsets between 300 and 700 km
- 1991
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 18:4, s. 645-648
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates that - under favorable conditions - by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up to 700 km, the maximum offset at which the authors attempted to record data.^Besides a powerful airgun array, a low noise environment at the recording site and the elimination of static shifts are the prerequisites to obtain refracted and reflected arrivals from the crust and upper mantle at such large offsets.^Primary arrivals detected at offsets between 400 and 700 km image the upper mantle from 70 to about 120 km depth.^Stacking of neighboring shots and/or receivers successfully increases the signal-to-noise ratio, if the traces have been corrected for offset differences, which requires knowledge of the apparent phase velocities.^The data presented here were collected in autumn 1989 during the BABEL Project on the Baltic Shield.
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| 4. |
- Buehler, Stefan, et al.
(författare)
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Scan asymmetries in AMSU-B data
- 2005
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 32:24, s. L2481-
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Tidskriftsartikel (refereegranskat)abstract
- A simple method of averaging measurements for different scan positions was used to quantify scan asymmetries in AMSU-B brightness temperatures for the sensors on the satellites NOAA 15, 16, and 17. The method works particularly well for the sounding channels 18 to 20. The asymmetries are small in most cases. In particular, asymmetries for Channel 18 are below 1.90, −0.53, and 0.49 K for NOAA 15, 16, and 17, respectively. On the other hand, it was found that the instrument on NOAA 15 has significant asymmetries for Channels 19 and 20, which seem to be related to the known radio frequency interference problem for this instrument. The use of the appropriate set of interference correction coefficients significantly reduces the asymmetry.
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| 5. |
- Buehler, Stefan, et al.
(författare)
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The impact of temperature errors on perceived humidity supersaturation
- 2003
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 30:14, s. 1759-
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo method is used to study the propagation of temperature uncertainties into relative humidity with respect to ice (RH i ) calculated from specific humidity. For a flat specific humidity distribution and Gaussian temperature uncertainties the resulting RH i distribution drops exponentially at high RH i values—much slower than a Gaussian. This agrees well with the RH i distribution measured by the Microwave Limb Sounder (MLS), which means that such remotely measured RH i distributions can be explained, at least partly, by temperature uncertainties.
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| 6. |
- Dhanaya, M. B., et al.
(författare)
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Proton entry into the near-lunar plasma wake for magnetic field aligned flow
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:2, s. 2913-2917
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Tidskriftsartikel (refereegranskat)abstract
- We report the first observation of protons in the near-lunar (100–200 km from the surface) and deeper (near anti-subsolar point) plasma wake when the interplanetary magnetic field (IMF) and solar wind velocity (vsw) are parallel (aligned flow; angle between IMF and vsw≤10°). More than 98% of the observations during aligned flow condition showed the presence of protons in the wake. These observations are obtained by the Solar Wind Monitor sensor of the Sub-keV Atom Reflecting Analyser experiment on Chandrayaan-1. The observation cannot be explained by the conventional fluid models for aligned flow. Back tracing of the observed protons suggests that their source is the solar wind. The larger gyroradii of the wake protons compared to that of solar wind suggest that they were part of the tail of the solar wind velocity distribution function. Such protons could enter the wake due to their large gyroradii even when the flow is aligned to IMF. However, the wake boundary electric field may also play a role in the entry of the protons into the wake.
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| 7. |
- Fatemi, Shahab, et al.
(författare)
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The lunar wake current systems
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:1, s. 17-21
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Tidskriftsartikel (refereegranskat)abstract
- We present the lunar wake current systems when the Moon is assumed to be a non-conductive body, absorbing the solar wind plasma. We show that in the transition regions between the plasma void, the expanding rarefaction region, and the interplanetary plasma, there are three main currents flowing around these regions in the lunar wake. The generated currents induce magnetic fields within these regions and perturb the field lines there. We use a three-dimensional, self-consistent hybrid model of plasma (particle ions and fluid electrons) to show the flow of these three currents. First, we identify the different plasma regions, separated by the currents, and then we show how the currents depend on the interplanetary magnetic field direction. Finally, we discuss the current closures in the lunar wake.
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| 8. |
- Guzewich, Scott D., et al.
(författare)
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Mars Science Laboratory Observations of the 2018/Mars Year 34 Global Dust Storm
- 2019
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 46:1, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- Mars Science Laboratory Curiosity rover observations of the 2018/Mars year 34 global/planet‐encircling dust storm represent the first in situ measurements of a global dust storm with dedicated meteorological sensors since the Viking Landers. The Mars Science Laboratory team planned and executed a science campaign lasting approximately 100 Martian sols to study the storm involving an enhanced cadence of environmental monitoring using the rover's meteorological sensors, cameras, and spectrometers. Mast Camera 880‐nm optical depth reached 8.5, and Rover Environmental Monitoring Station measurements indicated a 97% reduction in incident total ultraviolet solar radiation at the surface, 30K reduction in diurnal range of air temperature, and an increase in the semidiurnal pressure tide amplitude to 40 Pa. No active dust‐lifting sites were detected within Gale Crater, and global and local atmospheric dynamics were drastically altered during the storm. This work presents an overview of the mission's storm observations and initial results.
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| 9. |
- Höpfner, M., et al.
(författare)
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The natural greenhouse effect of atmospheric oxygen (O2) and nitrogen (N2)
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39:10
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Tidskriftsartikel (refereegranskat)abstract
- The effect of collision-induced absorption by molecular oxygen (O 2) and nitrogen (N 2) on the outgoing longwave radiation (OLR) of the Earth's atmosphere has been quantified. We have found that on global average under clear-sky conditions the OLR is reduced due to O 2 by 0.11 Wm -2 and due to N 2 by 0.17 Wm -2. Together this amounts to 15% of the OLR-reduction caused by CH 4 at present atmospheric concentrations. Over Antarctica the combined effect of O 2 and N 2 increases on average to about 38% of CH 4 with single values reaching up to 80%. This is explained by less interference of H 2O spectral bands on the absorption features of O 2 and N 2 for dry atmospheric conditions.
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| 10. |
- John, V. O., et al.
(författare)
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The impact of ozone lines on AMSU-B radiances
- 2004
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 31:21, s. L21108-
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Tidskriftsartikel (refereegranskat)abstract
- The impact of ozone lines on Advanced Microwave Sounding Unit-B (AMSU-B) radiances was investigated using a line-by-line radiative transfer model. The impact is found to be the largest for channel 18 (183.31 ± 1.00 GHz), with a maximum up to about 0.5 K. The channels 17 (150 GHz) and 20 (183.31 ± 7.00 GHz) are also marginally affected by the ozone lines. The magnitude of the impact shows an interesting dependence on the channel 18 brightness temperature which implies that the effect is not just an offset to the brightness temperature.
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