Effect of Electron Pressure on the Grad–Shafranov Reconstruction of Interplanetary Coronal Mass Ejections     

Qiang Hu  C. J. Farrugia  V. A. Osherovich  C. Möstl  A. Szabo  K. W. Ogilvie  R. P. Lepping 《Solar physics》2013,284(1):275-291

We investigate the effect of electron pressure on the Grad–Shafranov (GS) reconstruction of Interplanetary Coronal Mass Ejection (ICME) structures. The GS method uses in situ magnetic field and plasma measurements to solve for a magnetohydrostatic quasi-equilibrium state of space plasmas. For some events, a magnetic flux-rope structure embedded within the ICME can be reconstructed. The electron temperature contributes directly to the calculation of the total plasma pressure, and in ICMEs its contribution often substantially exceeds that of proton temperature. We selected ICME events observed with the Wind spacecraft at 1 AU and applied the GS reconstruction method to each event for cases with and without electron temperature measurements. We sorted them according to the proton plasma β (the ratio of proton plasma pressure to magnetic pressure) and the electron-to-proton temperature ratio. We present case studies of three representative events, show the cross sections of GS reconstructed flux-rope structure, and discuss the electron pressure contribution to key quantities in the numerical reconstruction procedure. We summarize and compare the geometrical and physical parameters derived from the GS reconstruction results for cases with and without electron temperature contribution. We conclude that overall the electron pressure effect on the GS reconstruction results contributes to a 10?–?20 % discrepancy in some key physical quantities, such as the magnetic flux content of the ICME flux rope observed at 1 AU.  相似文献   

Magnetic Clouds at/near the 2007?�C?2009 Solar Minimum: Frequency of Occurrence and Some Unusual Properties     

R. P. Lepping  C.-C. Wu  D. B. Berdichevsky  A. Szabo 《Solar physics》2011,274(1-2):345-360

Magnetic clouds (MCs) have been identified for the period 2007??C?2009 (at/near the recent solar minimum) from Wind data, then confirmed through MC parameter fitting using a force-free model. A dramatic increase in the frequency of occurrence of these events took place from the two early years of 2007 (with five MCs) and 2008 (one MC) compared to 2009 (12 MCs). This pattern approximately mirrors the occurrence-frequency profile that was observed over a three-year interval 12 years earlier, with eight events in 1995, four in 1996, and 17 in 1997, but decreased overall by a factor of 0.62 in number. However, the average estimated axial field strength [??|B _O|??] taken over all of the 18 events of 2007??C?2009 (called the ??recent period?? here) was only 11.0 nT, whereas ??|B _O|?? for the 29 events of 1995??C?1997 (called the ??earlier period??) was 16.5 nT. This 33% average drop in ??|B _O|?? is more or less consistent with the decreased three-year average interplanetary magnetic field intensity between these two periods, which shows a 23% drop. In the earlier period, the MCs were clearly of mixed types but predominantly of the South-to-North type, whereas those in the recent period are almost exclusively the North-to-South type; this change is consistent with global solar field changes predicted by Bothmer and Rust (Geophys. Monogr. Ser. 99, 139, 1997). As we have argued in earlier work (Lepping and Wu, J. Geophys. Res. 112, A10103, 2007), this change should make it possible to carry out (accurate short-term) magnetic storm forecasting by predicting the latter part of an MC from the earlier part, using a good MC parameter-fitting model with real-time data from a spacecraft at L₁, for example. The recent set??s average duration is 15.2 hours, which is a 27% decrease compared to that of the earlier set, which had an average duration of 20.9 hours. In fact, all physical aspects of the recent MC set are shown to drop with respect to the earlier set; e.g., as well as the average internal magnetic field drop, the recent set had a somewhat low average speed of 379 km?s^?1 (5% drop), and the average diameter had a 24% drop. Hence, compared to the earlier set, the recent set consists of events that are smaller, slightly slower, and weaker in every respect (and fewer in number), but in a relative sense the two three-year sets have similar frequency-of-occurrence profiles. It is also interesting that the two sets have almost the same average axial inclinations, i.e., axial latitude ??31° (in GSE). These MC characteristics are compared to relevant solar features and their changes. A preliminary assessment of the statistics on possible shocks and pressure pulses upstream of these recent MCs yields the following: About 28% of the MCs, at most, had shocks, and 33% had shocks and/or pressure pulses. These are low values, since typically the percentage of cases with shocks is about 50%, and the percentage with shocks and/or pressure pulses is usually about 75%.  相似文献   

Prioritisation of sub-watersheds based on earth observation data of agricultural dominated northern river basin of India     

Sandeep Kumar Yadav  Alok Dubey  Szabo Szilard 《国际地球制图》2018,33(4):339-356

The Upper Tons River Basin of North India has been selected for prioritisation of sub-watersheds (SW) based on morphometric parameters with respect to groundwater derived from topographic sheets and CARTOSAT data. There are 10 SW have been delineated in the region, high stream frequency (F_s) values of SW (1–5) and SW-9 indicated the occurrence of steep slopes, less permeable rocks, greater runoff, less infiltration possibility. Further, these regions have been predicted as poor groundwater potentialities. SW-2 has been identified as poorest groundwater potential zone, whereas SW-4 and SW (6–8) regions possess good permeable bed rocks. The Drainage density (D_d) map demonstrated that the middle south-west region possesses higher D_d whereas northeastern regions contain lower D_d. Further, the areal parameters indicate elongated shape of the basin, hilly region has moderate to steeper ground slope. The outcomes of work have potential to manage groundwater and to ameliorate the flash flood and droughts.  相似文献   

Uranium-series dating of lacustrine limestones from pan deposits with final Acheulian assemblage at Rooidam,Kimberley district,South Africa     

B.J. Szabo  K.W. Butzer 《Quaternary Research》1979,11(2):257-260

Lacustrine limestone samples from sedimentary pan deposits at Rooidam, near Kimberley, South Africa, that contain late Acheulian (Fauresmith) artifacts have been dated by ${}^{230}\text{Th}{}^{234}\text{U}$ and ${}^{231}\text{Pa}{}^{235}\text{U}$ methods. Results indicate a minimum age of about 200,000 yr B.P. for the terminal Acheulian in the interior of South Africa.  相似文献   

Ages of subsurface stratigraphic intervals in the Quaternary of Enewetak Atoll,Marshall Islands     

B.J. Szabo  J.I. Tracey  E.R. Goter 《Quaternary Research》1985,23(1):54-61

Drill cores of Enewetak Atoll, Marshall Islands, reveal six stratigraphic intervals, numbered in downward sequence, which represent vertical coral growth during Quaternary interglaciations. Radiocarbon dates indicate that the Holocene sea transgressed the emergent reef platform by about 8000 yr B.P. The reef grew rapidly upward (about 5 to 10 mm/yr) until about 6500 yr B.P. Afterward vertical growth slowed to about 0.5 mm/yr, then lateral development became dominant during the last several thousand years. The second interval is dated at 131,000 ± 3000 yr B.P. by uranium series. This unit correlates with oxygen-isotope substage 5e and with terrace VIIa of Huon Peninsula, New Guinea, and of Main Reef-2 terrace at Atauro Island. The third interval is not dated because corals were recrystallized and it is tentatively correlated with either oxygen-isotope stages 7 or 9. The age of the fourth interval is estimated at 454,000 ± 100,000 yr B.P. from measured ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios. This unit is correlated with either oxygen-isotope stage 9, 11, or 13.  相似文献   

Large-scale structure of the sun's corona from radio observations using the Clark Lake Radioheliograph     

M. R. Kundu  T. E. Gergely  E. J. Schmahl  A. Szabo  R. Loiacono  Z. Wang  R. A. Howard 《Solar physics》1987,108(1):113-129

We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona.  相似文献   

Comparison of the deflection of the vertical components computed by astro-geodetic, gravimetric and topographic-isostatic techniques     

Bela Szabo 《Journal of Geodesy》1962,36(3):227-242

Three different types of deflection of the vertical components wre computed at a number of selected astronomical stations in the south central United States. Astro-geodetic deflections were obtained from the differences between the astronomical and geodetic coordinates of each station. Gravimetric deflections were computed from isostatic anomalies. The isostatic isoanomaly charts used in this computation were constructed from data obtained by correcting point values taken from existing free-air isoanomaly charts for the effects of the Bouguer reduction and the topographic-isostatic reduction. It is felt that this procedure substantially reduces the labor involved in making isostatic reductions without sacrificing accuracy appreciably. Topographic-isostatic deflections were computed by Hayford's Method as modified by Orlin. The differences between the three types of deflection components are compared and conclusions made concerning their accuracy and utility. Aerounautical Chart and Information Center  相似文献