The Millstone Hill incoherent scatter (IS) radar is used to measure spectra close to perpendicular to the Earth's magnetic field, and the data are fit to three different forward models to estimate ...ionospheric temperatures. IS spectra measured close to perpendicular to the magnetic field are heavily influenced by Coulomb collisions, and the temperature estimates are sensitive to the collision operator used in the forward model. The standard theoretical model for IS radar spectra treats Coulomb collisions as a velocity independent Brownian motion process. This gives estimates of Te/Ti < 1 when fitting the measured spectra for aspect angles up to 3.6°, which is a physically unrealistic result. The numerical forward model from Milla and Kudeki (2011, https://doi.org/10.1109/TGRS.2010.2057253) incorporates single‐particle simulations of velocity‐dependent Coulomb collisions into a linear framework, and when applied to the Millstone data, it predicts the same Te/Ti ratios as the Brownian theory. The new approach is a nonlinear particle‐in‐cell (PIC) code that includes velocity‐dependent Coulomb collisions which produce significantly more collisional and nonlinear Landau damping of the measured ion‐acoustic wave than the other forward models. When applied to the radar data, the increased damping in the PIC simulations will result in more physically realistic estimates of Te/Ti. This new approach has the greatest impact for the largest measured ionospheric densities and the lowest radar frequencies. The new approach should enable IS radars to obtain accurate measurements of plasma temperatures at times and locations where they currently cannot.
Key Points
Millstone Hill measured incoherent scatter spectra at small aspect angles to test different models of determining ionospheric temperatures
Collisions narrowed measured spectra at aspect angles less than 4.6° for high densities, and at angles less than 1.25° for low densities
A nonlinear particle‐in‐cell forward model is shown to produce larger, more realistic, Te/Ti estimates than current forward models
A prominent ionospheric longitudinal variation at midlatitudes, in particular, over the continental US, was found recently. This variation is characterized as a higher east‐side electron density in ...the evening and a higher west‐side electron density in the morning, and with clear seasonal and solar activity dependencies. A combined effect of geomagnetic declination and changing zonal winds was proposed to explain it. This paper represents a comprehensive investigation of this effect by examining climatology for both electron density longitudinal differences and the nighttime zonal winds in the eastern US. Electron density is from incoherent scatter radar extra‐wide coverage experiments during 1978–2011 over Millstone Hill for which the spatial separation of the data can be up to 50° in longitude. The thermospheric zonal wind is from the on‐site Fabry‐Perot interferometer measurements during 1989–2001. The observed zonal wind climatology is found to be perfectly consistent with the expectation based on the east‐west electron density differences in terms of local time, seasonal, and solar cycle dependencies. The correlation between the zonal wind and the east‐west differential ratio is extremely high with an overall correlation coefficient of 0.93. The observed time delay of ∼3 hours in the response of electron density differences to zonal winds is a marked feature. Thus these results confirm positively the declination‐zonal wind mechanism and provide new insight into longitudinal variations at midlatitudes for other geographic sectors.
Key Points
Causes of a new type of ionospheric longitudinal variations at midlatitudes
East‐west Ne differences over the eastern US is highly corrected to zonal winds
The declination‐zonal wind effect can explain the longitudinal differences
•Ionospheric responses to a solar eclipse over MHO after 33 years.•A 40% reduction in COSMIC RO-measured electron densities.•Presence of wave-like signatures during the eclipse day.
Herein, we report ...on the ionospheric responses to a total solar eclipse that occurred on 21 August 2017 over the US region. Ground-based GPS total electron content (TEC) data along with ground-based measurements (Millstone Hill Observatory (MHO) and digital ionosondes) and space-based measurements (COSMIC radio occultation (RO) technique) allowed us to identify eclipse-associated ionospheric responses. TEC data at ~20°, ~30°, and ~40°N latitudes from the west to east longitudes show not only considerable depression but also wave-like characteristics in TEC both in the path of totality and away from it, exclusively on the day of eclipse. Interestingly, the observed depressions are associated with lesser (higher) magnitudes at stations over which the solar obscuration percentage was meager (significant), a clear indication of bow-wave-like features. The MHO observes a 30% reduction in F2-layer electron densities between 180 and 220 km on eclipse day. Ionosonde-scaled parameters over Boulder (40.4°N, 100°E) and Austin (30.4°N, 94.4°E) show a significant decrease in critical frequencies while an altitude elevation is seen in the virtual heights of the F-layer only during the eclipse day and that decreases are associated with wave-like signatures, which could be attributed to eclipse-generated waves. The estimated vertical electron density profile from the COSMIC RO-based technique shows a maximum depletion of 40%. Relatively intense and moderate depths of TEC depression, considerable reductions in the F2-layer electron densities measured by the MHO and COSMIC RO-measured densities at the F2-layer peak, and elevations in virtual heights and reduction in the critical frequencies measured by ionosondes during the eclipse day could be due to the eclipse-induced dynamical effects such as gravity waves (GWs) and their associated electro-dynamical effects (modification of ionospheric electric fields due to GWs).
SUMMARY
An evaluation of prospective shale gas reservoir intervals in the Bowland Shale is presented using a wireline log data set from the UK's first shale gas exploration well. Accurate ...identification of such intervals is crucial in determining ideal landing zones for drilling horizontal production wells, but the task is challenging due to the heterogeneous nature of mudrocks. This heterogeneity leads to stratigraphic variations in reservoir quality and mechanical properties, and leads to complex geophysical behaviour, including seismic anisotropy. We generate petrophysical logs such as mineralogy, porosity, and organic content and calibrate these to the results of core studies. If ‘reservoir quality’ is defined by combined cut-offs relating to these parameters, we find that over 100 m of reservoir quality shale is present in the well, located primarily within the upper section. To examine the link between geophysical signature and rock properties, an isotropic rock physics model is developed, using effective medium theories, to recreate the elastic properties of the shale and produce forward-looking templates for subsequent seismic inversion studies. We find that the mineralogical heterogeneity in the shale has a profound impact on modelled elastic properties, obscuring more discrete changes due to porosity, organic content and water saturation and that the best reservoir quality intervals of the shale bear a distinctive response on rock physics cross-plots. Finally, we consider the density of natural fractures in the shale by developing an anisotropic rock physics model to reflect high-angle fractures observed on micro-imagery logs. We invert crack density using shear wave splitting well log data and find a crack density of up to 4 per cent which correlates well with micro-imagery observations. Our work further supports previous authors’ core-based studies in concluding that the Bowland Shale holds good reservoir characteristics, and we propose that there are multiple intervals within the shale that could be targeted with stacked horizontal wells, should those intervals’ mechanical properties also be suitable and there be adequate stress barriers between to restrict vertical hydraulic fracture growth. Finally, our rock physics templates may provide useful tools in interpreting pre-stack seismic data sets in prospective areas of the Bowland Shale and picking the best locations for drilling wells.
Nian zhuan has its aroma as one of the perceived principal characteristics. The current study was aimed mainly to investigate the potential to include the aroma of nian zhuan as a new target ...criterion into the green wheat product chain. By improving the conditions for the traditional processing of nian zhuan, the optimal processing conditions were determined as green wheat (GW) 14 d, steaming the green wheat with the skin (SGWS) 26 min and cooked green wheat peeled (CGWP) 280 min, to evaluate the feasibility of using electronic nose (E-nose) and gas chromatography mass spectrometry (GC-MS) to discriminate nian zhuan in different stages. E-nose was used to recognize nian zhuan odors in different processing stages, and GC-MS to identify the individual volatile compounds. A total of 139 volatile compounds were detected by GC-MS, of which 71 key were screened by
t
-test (
P
< 0.01). The W1W, W1S, W2W and W2S sensors of E-nose gave higher responses to all samples, and effectively discriminated the samples. The most volatile compounds were produced in the millstone milling (MSM) stage of nian zhuan, and millstone could promote the release of volatile compounds from cooked green wheat by milling.
Ionospheric ion temperature Ti is an excellent approximation to neutral temperature Tn in the thermosphere, especially for altitudes below 300 km. This analysis of long‒term Ti trends in the F region ...over different local times is based on a database of incoherent scatter radar (ISR) observations spanning more than three solar cycles during 1968–2006 at Millstone Hill and represents an extended effort to a prior study focusing on noon‒time only. This study provides important information for understanding the difference between the ISR and other results. A gross average of the Ti trend at heights of Ti ∼ Tn (200–350 km) is ∼ −4 K/decade, a cooling trend close to the Tn estimation based on the satellite neutral density data. However, there exists considerable variability in the cooling: it is strong during the day and very weak during the night with a large apparent warming at low altitudes (200–350 km); it is strong at solar minimum for both daytime and nighttime. The strongest cooling for altitudes below 375 km occurs around 90–120 solar flux units of the 10.7 cm solar flux, not at the lowest solar flux. There appears more cooling toward high magnetic activity, but this dependency is very weak. No consistent and substantial seasonal dependency across different heights was found. We speculate that a fraction of the observed cooling trend may be contributed by a gradual shifting away from the sub‒auroral region at Millstone Hill, as part of the secular change in the Earth's magnetic field. In this 39 year long series of data record, two anomalous Ti drops were noticed, and we speculate on their connection to volcano eruptions in 1982 and 1991.
Key Points
Ti trend at altitudes of Ti~Tn close to ‐4K/decade as a gross daily average
Large day‐night, solar min‐max, and minor magnetic activity dependencies
Potential impacts from magnetic field secular changes
Technological Heritage of Persian Windmills Mishmastnehi, Moslem
Iran : journal of the British Institute of Persian Studies,
08/2021, Letnik:
ahead-of-print, Številka:
ahead-of-print
Journal Article
Recenzirano
Persian windmills are usually referred to as the earliest windmills in the history of technology. These windmills, well-known for their vertical axle design, are distributed over the Irano-Afghan ...borderland. This multidisciplinary investigation on windmills and their millstones from eastern Iran shows that there are various types of Persian windmills, despite their similar features. Four clusters of windmills exist in different regions of eastern Iran, distinctive in their construction, mechanical system, and types of their millstones. Three groups from the semi-highland of eastern Iran used natural rocks for their millstone, whereas the fourth group in the lowland applied artificial millstones made by a complex pyrotechnolgy. Functional windmills have been present only in the semi-highland but have not been reported from the lowland since the beginning of the last century. This article sheds light on technical details and the history of this earliest known type of windmill and helps their restoration process by providing an appropriate typology.
This paper studies the three-dimensional (3-D) ionospheric electron density variation over the continental US and adjacent regions during the August 2017 Great American Solar Eclipse event, using ...Millstone Hill incoherent scatter radar observations, ionosonde data, the Swarm satellite measurements, and a new TEC-based ionospheric data assimilation system (TIDAS). The TIDAS data assimilation system can reconstruct a 3-D electron density distribution over continental US and adjacent regions, with a spatial–temporal resolution of 1∘× 1∘ in latitude and longitude, 20 km in altitude, and 5 min in universal time. The combination of multi-instrumental observations and the high-resolution TIDAS data assimilation products can well represent the dynamic 3-D ionospheric electron density response to the solar eclipse, providing important altitude information and fine-scale details. Results show that the eclipse-induced ionospheric electron density depletion can exceed 50% around the F2-layer peak height between 200 and 300 km. The recovery of electron density following the maximum depletion exhibits an altitude-dependent feature, with lower altitudes exhibiting a faster recovery than the F2 peak region and above. The recovery feature was also characterized by a post-eclipse electron density enhancement of 15–30%, which is particularly prominent in the topside ionosphere at altitudes above 300 km.
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