281 research outputs found
Global Magnetospheric Response to an Interplanetary Shock: THEMIS Observations
No full textWe investigate the global response of geospace plasma environment to an interplanetary shock at approx. 0224 UT on May 28, 2008 from multiple THEMIS spacecraft observations in the magnetosheath (THEMIS B and C) and the mid-afternoon (THEMIS A) and dusk magnetosphere (THEMIS D and E). The interaction of the transmitted interplanetary shock with the magnetosphere has global effects. Consequently, it can affect geospace plasma significantly. After interacting with the bow shock, the interplanetary shock transmitted a fast shock and a discontinuity which propagated through the magnetosheath toward the Earth at speeds of 300 km/s and 137 km/s respectively. THEMIS A observations indicate that the plasmaspheric plume changed significantly by the interplanetary shock impact. The plasmaspheric plume density increased rapidly from 10 to 100/ cubic cm in 4 min and the ion distribution changed from isotropic to strongly anisotropic distribution. Electromagnetic ion cyclotron (EMIC) waves observed by THEMIS A are most likely excited by the anisotropic ion distributions caused by the interplanetary shock impact. To our best knowledge, this is the first direct observation of the plasmaspheric plume response to an interplanetary shock's impact. THEMIS A, but not D or E, observed a plasmaspheric plume in the dayside magnetosphere. Multiple spacecraft observations indicate that the dawn-side edge of the plasmaspheric plume was located between THEMIS A and D (or E)
Magnetopause reconnection across wide local time
No full textDuring April to July 2007 a combination of 10 spacecraft provided simultaneous monitoring of the dayside magnetopause across a wide range of local times. The array of four Cluster spacecraft, separated at large distances (10 000 km), were traversing the dawn-side magnetopause at high and low latitudes; the five THEMIS spacecraft were often in a 4 + 1 grouped configuration, traversing the low latitude, dusk-side magnetosphere, and the Double star, TC-1 spacecraft was in an equatorial orbit between the local times of the THEMIS and Cluster orbits. We show here a number of near simultaneous conjunctions of all 10 spacecraft at the magnetopause. One conjunction identifies an extended magnetic reconnection X-line, tilted in the low latitude, sub-solar region, which exists together with active anti-parallel reconnection sites extending to locations on the dawn-side flank. Oppositely moving FTE's are observed on all spacecraft, consistent with the initially strong IMF By conditions and the comparative locations of the spacecraft both dusk-ward and dawn-ward of noon. Comparison with other conjunctions of magnetopause crossings, which are also distributed over wide local times, supports the result that reconnection activity may occur at many sites simultaneously across the sub-solar and flank magnetopause, but linked to the large scale (extended) configuration of the merging line; broadly depending on IMF orientation. The occurrence of MR therefore inherently follows a "component" driven scenario irrespective of the guide field conditions. Some conjunctions allow the global magnetopause response to IMF changes to be observed and the distribution of spacecraft can directly confirm its shape, motion and deformation at local noon, dawn and dusk-side, simultaneously
Current reduction in a pseudo-breakup event: THEMIS observations
No full textPseudo-breakup events are thought to be generated by the same physical processes as substorms. This paper reports on the cross-tail current reduction in an isolated pseudo-breakup observed by three of the THEMIS probes (THEMIS A (THA), THEMIS D (THD), and THEMIS E (THE)) on 22 March 2010. During this pseudo-breakup, several localized auroral intensifications were seen by ground-based observatories. Using the unique spatial configuration of the three THEMIS probes, we have estimated the inertial and diamagnetic currents in the near-Earth plasma sheet associated with flow braking and diversion. We found the diamagnetic current to be the major contributor to the current reduction in this pseudo-breakup event. During flow braking, the plasma pressure was reinforced, and a weak electrojet and an auroral intensification appeared. After flow braking/diversion, the electrojet was enhanced, and a new auroral intensification was seen. The peak current intensity of the electrojet estimated from ground-based magnetometers, ~0.7 × 105 A, was about 1 order of magnitude lower than that in a typical substorm. We suggest that this pseudo-breakup event involved two dynamical processes: a current-reduction associated with plasma compression ahead of the earthward flow and a current-disruption related to the flow braking/diversion. Both processes are closely connected to the fundamental interaction between fast flows, the near-Earth ambient plasma, and the magnetic field
Database: THEMIS magnetopause crossings between 2007 and mid-2022
No full textDatabase of THEMIS observations of magnetopause crossings created for and used in:
Grimmich, N., Plaschke, F., Archer, M. O., Heyner, D., Mieth, J. Z. D., Nakamura, R., & Sibeck, D. G. (2023). Study of extreme magnetopause distortions under varying solar wind conditions.
Journal of Geophysical Research: Space Physics, 128, e2023JA031603. https://doi.org/10.1029/2023JA031603.
See section 3 of that publication for a detailed description of the identification process.
For further questions, please contact the corresponding author at [email protected]
Interplanetary magnetic field rotations followed from L1 to the ground : the response of the Earth's magnetosphere as seen by multi-spacecraft and ground-based observations
No full textA study of the interaction of solar wind magnetic field rotations with the Earth's magnetosphere is performed. For this event there is, for the first time, a full coverage over the dayside magnetosphere with multiple (multi)spacecraft missions from dawn to dusk, combined with ground magnetometers, radar and an auroral camera, this gives a unique coverage of the response of the Earth's magnetosphere. After a long period of southward IMF Bz and high dynamic pressure of the solar wind, the Earth's magnetosphere is eroded and compressed and reacts quickly to the turning of the magnetic field. We use data from the solar wind monitors ACE and Wind and from magnetospheric missions Cluster, THEMIS, DoubleStar and Geotail to investigate the behaviour of the magnetic rotations as they move through the bow shock and magnetosheath. The response of the magnetosphere is investigated through ground magnetometers and auroral keograms. It is found that the solar wind magnetic field drapes over the magnetopause, while still co-moving with the plasma flow at the flanks. The magnetopause reacts quickly to IMF Bz changes, setting up field aligned currents, poleward moving aurorae and strong ionospheric convection. Timing of the structures between the solar wind, magnetosheath and the ground shows that the advection time of the structures, using the solar wind velocity, correlates well with the timing differences between the spacecraft. The reaction time of the magnetopause and the ionospheric current systems to changes in the magnetosheath Bz seem to be almost immediate, allowing for the advection of the structure measured by the spacecraft closest to the magnetopause
Small and meso-scale properties of a substorm onset auroral arc
No full textInternational audienceWe present small and meso-scale properties of a substorm onset arc observed simultaneously by the Reimei and THEMIS satellites together with ground-based observations by the THEMIS GBO system. The optical observations revealed the slow equatorward motion of the growth-phase arc and the development of a much brighter onset arc poleward of it. Both arcs showed the typical particle signature of electrostatic acceleration in an inverted-V structure together with a strong Alfvén wave acceleration signature at the poleward edge of the onset arc. Two THEMIS spacecraft encountered earthward flow bursts around the times the expanding optical aurora reached their magnetic footprints in the ionosphere. The particle and field measurements allowed for the reconstruction of the field-aligned current system and the determination of plasma properties in the auroral source region. Auroral arc properties were extracted from the optical and particle measurements and were used to compare measured values to theoretical predictions of the electrodynamic model for the generation of auroral arcs. Good agreement could be reached for the meso-scale arc properties. A qualitative analysis of the internal structuring of the bright onset arc suggests the operation of the tearing instability which provides a 'rope-like' appearance due to advection of the current in the sheared flow across the arc. We also note that for the observed parameters ionospheric conductivity gradients due to electron precipitation will be unstable to the feedback instability in the ionospheric Alfvén resonator that can drive structuring in luminosity over the range of scales observed
Mechanism of substorm current wedge formation: THEMIS observations
No full textThis paper presents THEMIS measurements of two substorm events to show how the substorm current wedge (SCW) is generated. In the late growth phase when an earthward flow burst in the near-Earth magnetotail brakes and is diverted azimuthally, pressure gradients in the X-and Y-directions are observed to increase in the pileup and diverting regions of the flow. The enhanced pressure gradient in the Y-direction is dawnward (duskward) on the dawnside (duskside) where a clockwise (counter-clockwise) vortex forms. This dawn-dusk pressure gradient drives downward (upward) field-aligned current (FAC) on the dawnside (duskside) of the flow, which, when combined with the FACs generated by the clockwise (counter-clockwise) vortex, forms the SCW. Substorm auroral onset occurs when the vortices appear, Near-Earth dipolarization onset is observed by the THEMIS spacecraft (probes) when a rapid jump in the Y-component of pressure gradient is detected. The total FACs from the vortex and the azimuthal pressure gradient are found to be comparable to the DP-1 current in a typical substorm. Citation: Yao, Z. H., et al. (2012), Mechanism of substorm current wedge formation: THEMIS observations, Geophys. Res. Lett., 39, L13102, doi:10.1029/2012GL052055.Geosciences, MultidisciplinarySCI(E)EI20ARTICLE13null3
Defining the base configuration for the THeMIS
No full textKäesolevas lõputöös uuris autor võimalust määratlemaks ettevõtte Milrem AS toote THeMIS baaskonfiguratsiooni. Autor seadis lõputöö eesmärgiks määratleda THeMIS’le uus baaskonfiguratsioon, mis võtaks arvesse ka müügikonfiguratsiooni mooduleid ja hõlmaks endas juba viimaste paigalduseks vajaminevaid detaile mis tuleb paigaldada varajastes koostamise etappides. Tehes seda saavutamaks kulude kokkuhoidu tootmises ja pakkudes hilisemalt kliendile mugavamat võimalust oma soetatud sõidukit modifitseerida lisamoodulitega.
Püstitatud eesmärgi lahendamiseks seadis autor paika mitme etapilise protsessi. Esimeses etapis uuris autor teema kohast kirjandust ja leidis peamised murekohad millele peab tähelepanu pöörama, lahendamaks antud uurimisprobleemi. Järgmise sammuna kaardistas autor ära hetkel olukorra, nii baaskonfiguratsiooni kui ka müügikonfiguratsiooni moodulid. Selle tarbeks kogus autor informatsiooni ettevõtte ERP süsteemist, teostas vaatlusi tootmises ja toetava tegevusena arutas ka antud probleemi tootmisjuhiga, kes suunas autorit ettevõtte siseselt õigete infoallikateni. Antud tegevuse tulemusena põhistas autor uurimisprobleemi. Selle tulemusena tekkis autoril ülevaade hetke olukorrast mille alusel oli võimalik teostada edasist analüüsi leidmaks neid müügikonfiguratsiooni detaile mida oleks mõislik lisada baaskonfiguratsiooni. Viimase etapina teostas autor majandusanalüüsi pakutud lahendustele müügikonfiguratsiooni mooduli kaupa. Lõputöö raames püstitatud uurimisküsimustele leidis autor kõigile vastuse.
Tulemusena pakkus autor välja kaks võimaliku lahendust, primaarne lahendus ja sekundaarne lahendus. Primaarne lahendus oleks järk järguline üleminek uuendatud baaskonfiguratsioonile müügikonfiguratsiooni moodulite kaupa, võttes arvesse müüdavate lisamoodulite mahtu. Kohene täielik baaskonfiguratsiooni muudatus oleks ettevõtte tootmisele majanduslikult kahjulik. Sekundaarne lahendus oleks olemasoleva disaini ülevaatamine, läbi mille oleks võimalik toote omahinda vähendada ja seeläbi parendada ka tasuvuspunkti.
Autor hindab oma lõputöö tulemusi ja järeldusi heaks. Plaani teostatavus kahjuks ei ole kohene, aga pikema ajaperioodi jooksul kindlasti tasuv. Antud muudatused vähendaksid töökoormust ettevõtte siseselt, muudaksid paindlikumaks järelteeninduse ja looksid ettevõttest Milrem AS ka parema kuvandi kliendi silmis. Antud lõputöö võimaldab edasiseid uuringuid ka tulevikus, täpsemalt autori välja pakutud sekundaarse lahenduse suunal.In this thesis, the author explored the possibility of defining the base configuration of the product THeMIS of the company Milrem AS. The author set the goal of the thesis to define a new base configuration for the THeMIS, which would also take into account the sales configuration modules and include the components required for their installation during the early stages of assembly.". The aim was to achieve cost savings in production and to offer the customer a more convenient way to modify their purchased vehicle with additional modules at a later stage.
To achieve this goal, the author established a multi-step process. In the first stage, the author reviewed relevant literature and identified the main issues that needed to be addressed to solve the research problem. The next step was to map the current situation, including both the base configuration and the sales configuration modules. For this purpose, the author gathered information from the company's ERP system, conducted observations in production, and, as a supporting activity, discussed the issue with the production manager, who directed the author to the appropriate internal sources of information. As a result of this activity, the author substantiated the research problem. This led to an overview of the current situation, which served as a basis for further analysis to identify those sales configuration components that would be reasonable to include in the base configuration. As the final step, the author carried out an economic analysis of the proposed solutions for each sales configuration module. The author was able to answer all the research questions posed in the thesis.
As a result, the author proposed two possible solutions: a primary solution and a secondary solution. The primary solution would be a gradual transition to an updated base configuration, module by module, based on the volume of additional modules sold. An immediate and complete change to the base configuration would be economically harmful to the company's production. The secondary solution would be to review the existing design, which could potentially lower the product’s cost price and thereby reduce the break-even point.
The author considers the results and conclusions of the thesis to be good. Unfortunately, the feasibility of the plan is not immediate, but over a longer period, it would certainly be profitable. These changes would reduce the internal workload of the company, make after-sales service more flexible, and improve the public image of Milrem AS in the eyes of customers. This thesis also enables further research in the future, particularly in the direction of the secondary solution proposed by the author
THEMIS observation of a magnetotail current sheet flapping wave
No full textA flapping wave was observed by THEMIS-B (P1) and THEMIS-C (P2) probes on the dawn side of the magnetotail, while the solar wind was generally stable. The magnetic activity was quite weak, suggesting that this flapping wave was generated by an internal instability, which normally occurs during magnetic quiet times. Our analysis shows that the flapping wave was propagating downward with a tail-aligned scale of at least 3.7 R-E and did not show much change in shape during its propagation from P1 to P2. Correlation analysis employed to estimate the time lag between the corresponding half waveforms of P1 and P2 shows that the propagating velocities along the current sheet normal directions were close to each other in the beginning, but increased linearly later on. The average wavelength of the flapping wave is approximately 4 R-E. Theoretical analysis suggests that the ballooning type wave model may not be the mechanism for the observed flapping wave, but that the magnetic double-gradient instability model is a more plausible candidate.Multidisciplinary SciencesSCI(E)[email protected]
Vareuptychia themis Zacca & Casagrande & Mielke & Huertas & Espeland & Freitas & Willmott & Nakahara & Lamas 2020, comb. nov.
No full textVareuptychia themis (Butler, 1867) comb. nov. (Figs 5–13, 19–23, 26–27, 29) Euptychia themis Butler, 1867a: 463 [nom. nud]. Euptychia themis Butler, 1867b: 104, pl. 12, fig. 13; syntypes: no locality. Lectotype male here designated: no locality; NHMUK (examined).— Butler, 1868: 16.— Kirby, 1871: 48.— Butler, 1877: 118.— Kirby, 1879: 132.—Godman, 1901: 653.— Kaye, 1921: 57.— Barcant, 1970: 159, 161, pl. 13, fig. 11.— Santin, 2004: 1056. Euptychia similis; Butler, 1867b: 109, pl. 12, fig. 10 [misidentification]. Euptychia undina Butler, 1870: 252; holotype: Nicaragua; NHMUK (examined).— Kirby, 1871: 643.— Butler, 1877: 118. Euptychia cleophes Godman & Salvin, 1889: 352 (partim) [misidentification]. Cissia themis; DeVries, 1987: pl. 48, figs. 20–21.—Singer & Ehrlich, 1993: 248.— Lamas, 2004: 218.— Nakahara et al., 2012: 359–362, figs. 1, 2A–2B, 3–4 (male, female, genitalia, distributional map).— Luis-Martínez et al., 2004: 349.—Hernández-Mejía et al., 2008: 125.— Luis-Martínez et al., 2011: 23.— Miller et al., 2012: 58.— Luis-Martínez et al., 2016: 216.— Cock, 2014: 11.— Marín et al., 2017: 774, fig. 4C.—Henao-Bañol & Gantiva, 2020: 187. Vareuptychia themis; Llorente-Bousquets et al., 1996: 45. Vareuptychia undina; Llorente-Bousquets et al., 1996: 45. Cissia undina; Luis-Martínez et al., 2004: 349.— Luis-Martínez et al., 2011: 23.— Luis-Martínez et al., 2016: 216. Yphthimoides maepius [misidentification]; Montero-Abril et al., 2009: 165. ‘Cissia’ similis; Zacca et al., 2018b: 351 [misidentification]. Diagnosis. Vareuptychia themis can be distinguished from its congener by the bipupilled ocellus in CuA 1 -CuA 2 and the shape of the lamella antevaginalis (Fig. 27). Male genitalia (Figs. 19–23). See above under ‘Redescription’ section. Female genitalia (Figs. 26–27). In addition to the characters mentioned in the generic description, the lateral plate does not reach the 8 th tergite. Lamella antevaginalis is large, wrinkled and half-orbicular in ventral view. The paired signa are dorsally located. Variation. The VW ground color varies significantly from pale to dark brown, as also observed by Nakahara et al. (2012), and it is not associated with seasonal polyphenism or geographical distribution. Some individuals have orangey yellow patches on the umbra similar to those found in V. similis. Some individuals have an additional ocellus without a pupil in 2A and the inner margin of the VHW (Fig. 8). Examination of the male genitalia of ten individuals from different localities (i.e. Mexico, El Salvador, and Venezuela) showed some variation in the size, shape and width of the tegumen, uncus, valva and aedeagus, in contrast to the observations of Nakahara et al. (2012). Conversely, female genitalia structures were found to be more conservative (mainly the shape of the lamella antevaginalis) but the presence/absence of the posterior apophysis and the size and width of the corpus bursae were variable among some individuals. Ecology and distribution. This species is distributed widely from Mexico to Colombia and Venezuela, and in Trinidad and Tobago (Barcant 1970; Cock 2014; DeVries 1987; Llorente-Bousquets 1996; Luis-Martínez et al. 2004; Hernández-Mejía et al. 2008; Luis-Martinez et al. 2011; Nakahara et al. 2012; Singer & Ehrlich 1991; plus examined material), at altitudes up to 2000 m (Fig. 29). Vareuptychia themis comb. nov. is sympatric and syntopic with V. similis in several localities in Mexico, such as Jalisco, Malinalco, Oaxaca, Sonora, Veracruz and Yucatán (Llorente-Bousquets 1996; Luis-Martinez et al. 2004; Hernández-Mejía et al. 2008; Luis-Martínez et al. 2011; E. Pfeiler pers. comm.; plus examined material), Guatemala (Baja Verapaz), Honduras (San Pedro Sula) and Venezuela (Aragua). Vareuptychia themis comb. nov. is multivoltine, flying all year. It has been recorded in deciduous and semideciduous forests along forest edges, and occasionally in open areas. In Costa Rica, this species is most abundant during the rainy season (Jun–Aug), and becomes less abundant as the dry season progresses (DeVries 1987). Similar to V. similis comb. rest., V. themis comb. nov. has been recorded feeding on decaying fruits, such as graviola (Annonaceae), sapote (Sapotaceae) and mango (Anacardiaceae) (Hernández-Mejía et al. 2008). Recorded larval host plants include undetermined species of Poaceae (DeVries 1987; Santin 2004). Type material, lectotype designation and taxonomic history. Butler (1867a) first introduced the name Euptychia themis as a nomen nudum, since no description or illustration was provided by the author, which fails to conform to Article 13 of the International Code of Zoological Nomeclature (ICZN 1999). The name became available when Butler (1867b) published an illustration of the species (pl. 12, fig. 13) in the supplementary material to his “Monograph of the genus Euptychia ”, although the locality of the specimen illustrated was not provided. One male specimen that agrees with the illustration of E. themis (Butler, 1867b, pl. 12, fig. 13) was found at NHMUK. This specimen has no locality label, although ‘Mexico’ is handwritten (but has been erased) on one label (Fig. 10), which also states that the specimen came from Hewitson’s collection, agreeing with the information provided by Butler (1867a). To fix the identity of the name, this male specimen is herein designated as the lectotype of E. themis; it has the following labels: /Type ♂ / Hewitson Coll. 79–69. Euptychia themis. Butl[er]. 1./ Euptychia themis Butler / B. M. Type No. Rh. 3201 Euptychia themis, ♂ Butl[er]./ BMNH(E) 982889/; and two others will be added later: / Lectotype / Lectotype Euptychia themis Butler, 1867. T. Zacca det. 2020/. NHMUK. Butler (1870) named Euptychia undina based on a single specimen (holotype) from Nicaragua (Fig. 9), being part of the type series of E. similis (see discussion under V. similis) and bearing Butler’s distinctive blue label for types. Examination of the male holotype of E. undina at the NHMUK confirmed that this specimen is, in fact, E. themis since it has two silvery pupils in ocellus CuA 1 -CuA 2 on the VHW. Examined material. 339 males and 125 females (21 specimens dissected)—see Supporting Information (S2).Published as part of Zacca, Thamara, Casagrande, Mirna M., Mielke, Olaf H. H., Huertas, Blanca, Espeland, Marianne, Freitas, André V. L., Willmott, Keith R., Nakahara, Shinichi & Lamas, Gerardo, 2020, Revalidation of Vareuptychia Forster, 1964, description of Vanima gen. nov., and notes on Euptychia cleophes Godman & Salvin, 1889 (Lepidoptera: Nymphalidae Satyrinae), pp. 1-34 in Zootaxa 4858 (1) on pages 11-13, DOI: 10.11646/zootaxa.4858.1.1, http://zenodo.org/record/441141
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