Tail Lobe Research Articles

Time Sequence of Magnetospheric Responses to a Southward IMF Turning

AbstractWe use MHD simulations to study the time sequence of magnetospheric responses to a synthetic event with a southward interplanetary magnetic field (IMF) turning. The onset of dayside magnetopause reconnection launches a weak rarefaction wave and sunward flow in the equatorial magnetosphere simultaneously with a tailward flow through the polar cap. This convection results in the accumulation of magnetic flux in the tail lobes and thinning of the tail current layer which provides favorable conditions for the onset of nightside reconnection. The onset of nightside reconnection about 40 min later closes the Dungey convection cycle, resulting in a second increase in the sunward flow in the equatorial plane. Variations of the magnetopause standoff distance as well as the size of the polar cap (PC) may indicate the onsets of the dayside and nightside reconnections. We compare the results of two MHD models and discuss their differences.

The Discrepancy between Observed and Predicted Heliospheric Energetic Neutral Atoms below Solar Wind Energy

Measuring energetic neutral atoms (ENAs) allows for the remote observation of ion populations from the frontiers of our heliosphere. In this study, we compare the ENAs observed with the IBEX-Lo instrument onboard the Interstellar Boundary Explorer with ENA predictions from two heliosphere models. In contrast to previous studies, this paper presents model-data comparisons for the energy range 50 eV–2 keV over one full solar cycle not only in the upwind direction (Voyager 1 and Voyager 2 sky directions), but also for the north pole, south pole, port tail lobe, and downwind directions. The two heliosphere models produce the same basic result: there is a large gap (1 to 2 orders of magnitude in ENA intensity at 100 eV) between ENA data and model predictions between 100 and 500 eV for all sky directions. The reason for this gap is not understood yet. While some explanations are plausible and will be investigated in future studies, other explanations are excluded.

Using machine learning to characterize solar wind driving of convection in the terrestrial magnetotail lobes

In order to quantitatively investigate the mechanism of how magnetospheric convection is driven in the region of magnetotail lobes on a global scale, we analyzed data from the ARTEMIS spacecraft in the deep tail and data from the Cluster spacecraft in the near and mid-tail regions. Our previous work revealed that, in the lobes near the Moon’s orbit, the convection can be estimated by using ARTEMIS measurements of lunar ions’ velocity. Based on that, in this paper, we applied machine learning models to these measurements to determine which upstream solar wind parameters significantly drive the lobe convection in magnetotail regions, to help us understand the mechanism that controls the dynamics of the tail lobes. The results demonstrate that the correlations between the predicted and measured convection velocities for the machine learning models (>0.75) are superior to those of the multiple linear regression model (∼0.23–0.43) in the testing dataset. The systematic analysis shows that the IMF and magnetospheric activity play an important role in influencing plasma convection in the global magnetotail lobes.

Ceratal autotomy as a defensive mechanism of the sacoglossan sea slug Placida kingstoni against a generalist crustacean predator

ABSTRACT Sacoglossan sea slugs have developed a variety of defence mechanisms against predation. Research on these mechanisms has focused primarily on the chemical defences of these slugs, and little information is available on nonchemical modes of defence, such as autotomy, a behaviour in which an organism voluntarily detaches body structures at a predetermined breakage point in response to danger or stress. Autotomy is diverse in sacoglossan sea slugs and has been well documented. Within Oxynidae, members can autotomize their tail and parapodial lobes, and slugs in Limapontiidae and Hermaeidae can detach their cerata. More recently, reports have been made of Elysia with the capacity to autotomize most of their body. However, despite the widespread assumption that autotomy in this group serves a defensive purpose, the effectiveness of the behaviour in ensuring survival against predation has seldom been examined. The objective of this study was to evaluate the role of autotomy in sacoglossans by assessing the effectiveness of ceratal autotomy in ensuring survival against the attacks of a generalist predator. Placida kingstoni is a small sacoglossan native to Florida and the Caribbean with the ability to autotomize its cerata. Individual P. kingstoni were exposed to shrimps of the Lysmata wurdemanni species complex for 10-min interactions. Most sea slugs were attacked by the predator, often more than once, but the majority of the slugs readily autotomized cerata and survived. Structure detachment was accompanied by the secretion of a mucus that facilitated the formation of ceratal clumps. Most of these clumps were consumed by the predator and effectively diverted their attention, allowing P. kingstoni to crawl away. In this species, the success of autotomy as a defensive strategy appears to be directly related to the palatability of autotomized cerata. The results of this study show that ceratal autotomy in P. kingstoni is an effective defence against predation. Autotomy is a behaviour with a high-energetic cost; however, it has convergently evolved within Heterobranchia on multiple occasions, and it is highly prevalent in cerata-bearing slugs. Although in sacoglossans much of this behaviour remains a mystery, this study provides a clear example of autotomy as a defensive mechanism.

Generation of Field‐Aligned Currents During Substorm Expansion: An Update

AbstractWe investigated generation processes of field‐aligned currents (FACs) that are abruptly intensified at the beginning of the substorm expansion phase by tracing a packet of the Alfvén wave backward in time from the onset position in the ionosphere in the global magnetohydrodynamics (MHD) simulation. The generation region is found in the near‐Earth plasma sheet, in which (a) azimuthally moving plasma pulls the magnetic field line, and performs negative work against the magnetic tension force to excite the Alfvén waves, (b) FACs are generated from the requirement of Ampère and Faraday laws, and (c) field‐perpendicular current is converted to FACs. We call this near‐Earth FAC dynamo. The plasma involved originates in the tail lobe region. When near‐Earth reconnection occurs in the plasma sheet, the plasma is accelerated earthward by the Lorentz force, and decelerated by the plasma pressure gradient force, followed by the Lorentz force. The flow is deflected to the west and east directions by the plasma pressure gradient force and the Lorentz force, resulting in the excitation of Alfvén waves and FACs. The Alfvén waves propagate along the magnetic field in the rest frame of the moving plasma. When it arrives at the ionosphere, the auroral electrojet starts developing and the substorm expansion phase begins. The near‐Earth FAC dynamo can be distinguished from the near‐Earth dynamo (J · E < 0, where J is the current density and E is the electric field). We suggest that the evolution of the substorm can be understood in terms of the development of FACs.

Plasma sheath around sunlit moon: monotonic and non-monotonic structures

ABSTRACTAn analytical investigation of the sheath formation over sunlit moon under the influence of observed solar ultraviolet/extreme ultraviolet radiation and solar wind plasma has been presented. Poisson’s equation is coupled with the latitude-dependent Fermionic photoelectrons, non-Maxwellian solar wind electrons and cold ions to derive the electric potential, electric field, and population density profiles within the photoelectron sheath. We notice that the high-energy photons of the solar spectra in addition to Lyman- α, significantly contribute in determining the surface charge and subsequent sheath structure. A traditional Debye (Type C) sheath forms around the terminator due to dominant plasma electron accretion and marginal photoemission. While moving towards the equator, the photoelectron contribution increases, yielding monotonic (Type B) and non-monotonic (Type A) sheath solutions over sunlit locations. The calculations show that the non-monotonic potential structures are more stable near the terminator region, while both types of potential structures are probable near the equator region for the nominal solar wind plasma. A vertical sheath extension of ∼60 m and ∼12 m is predicted for typical solar wind plasma at the equator corresponding to Type A and Type B sheath, respectively. Under exotic plasma conditions (e.g. Earth’s magnetospheric tail lobe, plasma sheet), non-monotonic solutions become stable for the photoemission-dominated region, and the entire sunlit lunar surface may acquire negative potential.

Energy Flux Through the Magnetopause During Flux Transfer Events in Hybrid-Vlasov 2D Simulations.

Solar wind-magnetosphere coupling drives magnetospheric dynamic phenomena by enabling energy exchange between magnetospheric and solar wind plasmas. In this study, we examine two-dimensional noon-midnight meridional plane simulation runs of the global hybrid-Vlasov code Vlasiator with southward interplanetary magnetic field driving. We compute the energy flux, which consists of the Poynting flux and hydrodynamic energy flux components, through the Earth's magnetopause during flux transfer events (FTEs). The results demonstrate the spatiotemporal variations of the energy flux along the magnetopause during an FTE, associating the FTE leading (trailing) edge with an energy injection into (escape from) the magnetosphere on the dayside. Furthermore, FTEs traveling along the magnetopause transport energy to the nightside magnetosphere. We identify the tail lobes as a primary entry region for solar wind energy into the magnetosphere, consistent with results from global magnetohydrodynamic simulations and observations.

The Dawn‐Dusk Tail Lobe Magnetotail Configuration and the Formation of Aurora Transpolar Arc

AbstractThe magnetotail configuration includes a northern tail lobe, a southern tail lobe, and a plasma sheet when IMF directs southward, as a result of the Dungey cycle. However, it is little known about the magnetotail configuration for northward IMF (NIMF) conditions. Using in situ data and corresponding simulations, we show that the magnetotail forms into a dawnside tail lobe and a duskside tail lobe under NIMF with significant By conditions. The data shows signatures related to magnetotail reconnection under such conditions. Cusp reconnection and such magnetotail reconnection may form a dawn‐dusk tail lobe configuration and its version of Dungey cycle. Simulation results also show that aurora transpolar arc may be caused by a process of reconfiguration of the dawn‐dusk tail lobe structure as a result of an IMF By reversal.

Effect of IMF By on the Entry of Solar Wind Ions Into the Near‐Earth Tail Lobe: Global Hybrid Simulation and MMS Observation

AbstractGlobal simulations predict that the low‐latitude mantle may be an important pathway for the solar wind entry into the tail magnetosphere close to the current sheet when interplanetary magnetic field (IMF) By dominates over IMF Bz. To evaluate this entry mechanism in the near‐Earth tail (X ∼ −10–−20 RE), we investigate the predictions from 3D global hybrid simulations as well as in situ observations by magnetospheric multiscale (MMS) spacecraft. The simulations predict that the low‐latitude mantle plasma can appear in the near‐Earth tail lobe extending inward approximately 5 RE from the flank magnetopause. The low‐latitude mantle plasma appears in the dawnside northern lobe and duskside southern lobe during positive IMF By, while the opposite asymmetry is seen during negative IMF By. After a change in the IMF By direction arriving at the bow shock nose, it takes another ∼15–30 min for the asymmetry to completely reverse to the opposite sense in the near‐Earth tail. We present six MMS events in the tail lobe showing that the existence and absence of the low‐latitude mantle plasma is consistent with the predicted asymmetries. Statistical analysis of 5 years of MMS observations shows that the dependencies of the magnitudes of the lobe densities and tailward field‐aligned flow speeds on the IMF By directions are consistent with the predicted contributions from the low‐latitude mantle plasma in the expected lobe regions.

A Statistical Study on Wide‐Amplitude Kinetic Alfvénic Pulse at 8–12RE in the Magnetotail by THEMIS Spacecraft From 2008 to 2010

AbstractUsing THEMIS spacecraft observations from 2008 to 2010, we perform statistical study on the wide‐amplitude kinetic Hall‐like Alfvénic wave (KAW) pulse in the near‐Earth tail region of 8–12 RE. The KAW pulse is identified by Ez‐By pulse with parallel‐predominantly Poynting flux (|P///PT| > 0.7) and large Ez/By ratio (|∆Ez/∆By | > VA, VA is Alfvénic velocity). Three typical events are presented. Therein, the KAW pulse on 24 March 2009 at the magnetic dipolarization is accompanied by the ion/electron dispersed structure (IDS/EDS; time of flight effect from reconnection source). Statistical study shows that the near‐Earth KAW pulse has a typical temporal scale of ∼15–25 s. The KAW pulses are mainly distributed in the plasma sheet boundary layer (PSBL) and tail lobe regions of β < 0.1 (β is the ratio of thermal pressure to magnetic pressure). The KAW pule at the PSBL/lobe has a wide distribution in the dawn‐dusk direction (−10 RE < |Y| < 10 RE), with the maximum occurrence at the midnight (|Y| < 4 RE). The KAW pulses at the PSBL/lobe are predominantly earthward‐propagating. Only a small number of the KAW pulses are tailward‐propagating. The earthward‐propagating pulse has a higher Poynting flux (PT) than tailward‐propagating pulse. The KAW pulse occurs during quiet time (AE < 200 nT) as well as substorm interval (AE > 200 nT). The substorm‐interval pulse has a higher Poynting flux than the quiet‐time pulse. Finally, tail reconnection is likely the significant source of the near‐Earth KAW pulses at 8–12 RE.

A Survey of 25 Years' Transpolar Voltage Data From the SuperDARN Radar Network and the Expanding‐Contracting Polar Cap Model

AbstractWe use 214,410 hourly observations of transpolar voltage, ΦPC, from 25 years' observations by the Super Dual Auroral Radar Network radars to confirm the central tenet of the expanding‐contracting polar cap model of ionospheric convection that ΦPC responds to both dayside and nightside reconnection voltages (ΦD and ΦN). We show that ΦPC not only increases at a fixed level of the nightside auroral electrojet AL index with increasingly southward interplanetary magnetic field (IMF) (identifying the well‐known effect of ΦD on ΦPC) but also with increasingly negative AL at a fixed southward IMF (identifying a distinct effect of ΦN on ΦPC). We also study the variation of ΦPC with time elapsed since the IMF last pointed southward, Δt, and show that low/large values occur when (−AL) is small/large. Lower numbers of radar echoes, ne, mean that the “map‐potential” reanalysis technique used to derive ΦPC is influenced by the model used: we present a sensitivity study of the effect of the threshold of ne required to avoid this. We show that for any threshold ne, ΦPC falls to about 15 kV for Δt greater than about 15 h, indicating any viscous‐like voltage ΦV is considerably smaller than this. It is shown that both ΦPC and (−AL) increase with increased solar wind dynamic pressure pSW, but not as much as the midlatitude geomagnetic index am. We conclude pSW increases both ΦD and ΦN through increasing the magnetic shear across the relevant current sheet but has a larger effect on midlatitude geomagnetic indices because of the effect of additional energy stored in the tail lobes.

Metastatic Non-Functional Pancreatic Neuroendocrine Tumor in a Patient With a Pathogenic TSC1 Mutation

Abstract Introduction: Tuberous sclerosis complex (TSC) is an autosomal dominant multisystem disorder caused by mutations in two tumor suppressor genes (TSC1 and TSC2) encoding proteins critical in cell growth and proliferation and is associated with an increased risk for benign and malignant tumors. Pancreatic neuroendocrine tumors (PNET) occur in 1.5-1.8% of patients with TSC. They have been primarily reported in TSC2, with only a few cases in the context of TSC1. We describe a non-functional metastatic PNET in a patient with a known pathogenic TSC1 mutation. Case Description: A 49-year old female with a past medical history of bipolar disease, a family history of TSC1 in a daughter, a known pathologic TSC1 mutation (c.2356C>T), and previous history of renal cell carcinoma (RCC) was evaluated for a pancreatic lesion with likely liver metastases. Two years prior to the presentation, a 10 mm pancreatic lesion was initially noted on the CT scan during a renal mass evaluation. Nephrectomy confirmed the RCC. Two years later, surveillance imaging revealed two new lesions in the liver, and the pancreatic lesion had enlarged to 1.3 cm. She denied symptoms suggestive of a functional PNET, and her physical exam was unremarkable. Gallium-68 dotatate (GA-68) PET/CT scan demonstrated avid lesions of both the pancreatic tail and left hepatic lobe. Biopsy of the 3 cm liver mass revealed a metastatic high-grade neuroendocrine carcinoma (mib-1 proliferation index of 15%) favoring a primary PNET. Immunohistochemical stains were positive for chromogranin A, synaptophysin, EMA, PAX 8, CK 20, and villin. Stains for CA 19-9 and CK 7 were negative. Biochemical testing suggested that the PNET was non-functional. Specifically, serum concentrations of gastrin, somatostatin, glucagon, glucose, C-peptide, proinsulin, pancreatic polypeptide, chromogranin A, and vascular endothelial growth factor were within normal limits. The patient underwent distal pancreatectomy and resection of the liver mass. Pathological specimens confirmed the diagnosis of a PNET. The patient remained asymptomatic and was monitored regularly with MRI and GA-68 PET/CT scans without further evidence of the disease for 1.5 years. Conclusions: We conclude that this patient harboring a c.2356C>T TSC1 mutation developed a non-functional metastatic PNET. PNET is a likely component of TSC1.

Magnetotail Configuration Under Northward IMF Conditions

AbstractDue to the sparsity of space probes, it is still not clear on how the magnetic structure of the magnetotail looks like and how it evolves when the interplanetary magnetic field (IMF) directs northward. This simulation study uses two different global magnetosphere magnetohydrodynamics (MHD) models to simulate two northward IMF events and study the evolution of the magnetotail. Both models show that the magnetotail may form a structure that is composed of a dawnside tail lobe and a duskside tail lobe, under northward IMF conditions with significant By, instead of a northern tail lobe and a southern tail lobe under southward IMF conditions. In this magnetic configuration, a tail lobe extends a domain from northern (southern) cusp to southern (northern) IMF. The larger the magnitude of IMF clock angle, the longer and wider the magnetotail. Such magnetic configuration suggests that magnetotail reconnection is possible to occur when the dawnside tail lobe contacts with the duskside tail lobe and thus a substorm is also possible to occur under northward IMF conditions with significant By.

Statistical Characteristics of Field‐Aligned Currents in the Plasma Sheet Boundary Layer

AbstractEnergy and momentum can be transferred from the magnetosphere to the ionosphere through field‐aligned currents (FACs), which show seasonal variations due to seasonal variation of the ionospheric conductance. Using Magnetospheric Multiscale Mission observations, we investigate the characteristics of kinetic‐scale (close to local ion inertial length) FACs in the plasma sheet boundary layer (PSBL), such as occurrence rate, magnitude, and carriers. The results show that: (1) the occurrence rates of FACs exhibit a trident distribution; they are also larger in the northern hemisphere than in the southern hemisphere, especially for the earthward FACs. (2) Distribution patterns vs. plasma β are different for the beam‐type and the flow‐type FACs. Flow‐type FACs are observed closer to the central plasma sheet (higher β), and their occurrence rate decreases linearly toward the tail lobe (lower β), while the beam‐type FACs are mainly and equally distributed within 0.1 < β < 1.0. (3) The magnitude of FACs shows little dependence on β, and generally increases closer to the Earth. (4) Occurrence rate and magnitude of FACs both increase during active periods, consistent with ionospheric observations. (5) The main carriers for FACs in the PSBL are thermal electrons, while cold electrons also contribute occasionally, especially during active periods. Hemispheric asymmetry of occurrence rate and dependence on geomagnetic activity of the kinetic‐scale FACs in the PSBL are consistent with FACs at ionospheric altitudes. This fact demonstrates that kinetic‐scale FACs are significant in magnetosphere‐ionosphere coupling and illustrates the possible ionospheric feedback effects to the magnetosphere in the nightside.

MMS Observations of Reconnection Separatrix Region in the Magnetotail at Different Distances From the Active Neutral X‐Line

AbstractThe region surrounding the reconnection separatrix consists of many particle and wave transient features (electron, cold and hot ion beams, Hall E&B fields, kinetic Alfvén, LH, etc. waves) whose pattern and parameters may vary depending on the distance from active neutral line. We study nine quick MMS entries into the plasma sheet boundary layer (PSBL) from the tail lobe to address the meso‐scale pattern and other characteristics of phenomena for active separatrix crossings as deduced from particle observations. The outermost thin layer (a fraction of ion inertial scale, di) of low‐density plasma consists of accelerated electron beams and lobe cold ions and displays density depletions (EBL region). It is followed by hot proton beam (PBL region) in which the plasma density grows from lobe‐like towards plasma sheet‐like values; the beam energy‐dispersion is used to estimate the distance from the active neutral line. Thin (usually ≤ di) region containing intense Hall‐like Ez perturbations (HR) usually overlaps with EBL and PBL regions. It often includes correlated B perturbations suggesting the Alfvén wave‐related transport from the reconnection source; the estimated Alfvénic ratio δE/(VA δB) varied between 0.3 and 1.3 in studied examples. The HR is associated with profound plasma property changes, including the heating of cold ion beams in its innermost part, it hosts intense structured field‐aligned currents and intense E‐field fluctuations. Surprisingly, most of abovementioned findings are valid for crossings observed at large distances from the reconnection region (exceeding a few tens Re or >100 di) except for longer time‐scales and larger spatial scales of the pattern.

Plasma Convection in the Terrestrial Magnetotail Lobes Measured Near the Moon's Orbit

AbstractIn order to study the plasma convection in the deep magnetotail lobes near lunar orbit, we investigated ions originating from the tenuous exosphere and surface of the Moon, which are measured by the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. Directly measuring the plasma convection in the tail lobes is difficult, due to the typically large positive spacecraft potential. In this work we show that in the terrestrial magnetotail near the Moon, the convection velocity can be estimated by measuring the velocity of lunar ions. Determining what factors control the lobe convection is important in understanding the linkage between the upstream conditions and the dynamics of the tail lobes. Based on systematic analysis of multiple ARTEMIS observations and OMNI data, we find that the interplanetary magnetic field (IMF) and magnetospheric activity plays an important role in controlling plasma convection in the near‐Moon lobes.

Flux Ropes Are Born in Pairs: An Outcome of Interlinked, Reconnecting Flux Tubes

AbstractFlux transfer events are transient magnetized plasma structures that are self‐balancing, rope‐like phenomena that can appear at the Earth's magnetopause when the interplanetary magnetic field is southward. The formation of this type of flux rope has been unclear. Using measurements of particles and magnetic fields on the MMS spacecraft, we find that rope‐like structures containing magnetospheric energetic electrons have exactly the same occurrence rate as those without magnetospheric electrons, independent of solar wind properties and location of observation. This equality is consistent with a pair of flux bundles being generated at the same time but displaced from each other as an outcome of their collision and resultant entanglement and reconnection. This entanglement reconnection produces one flux rope with two ends connected to the magnetosphere and the other connected on both ends to the shocked solar wind. Away from the subsolar entanglement zone, reconnection transports magnetic flux from the “closed” magnetosphere to the “open” tail lobes, as predicted by Dungey (1961, https://doi.org/10.1103/PhysRevLett.6.47).

A new millipede-parasitizing horsehair worm, Gordius chiashanus sp. nov., at medium altitudes in Taiwan (Nematomorpha, Gordiida).

Gordius chiashanussp. nov., a newly described horsehair worm that parasitizes the Spirobolus millipede, is one of the three described horsehair worm species in Taiwan. It is morphologically similar to G. helveticus Schmidt-Rhaesa, 2010 because of the progressively broadening distribution of bristles concentrated on the male tail lobes, but it is distinguishable from G. helveticus because of the stout bristles on the mid-body. In addition, a vertical white stripe on the anterior ventral side and areoles on the inside wall of the cloacal opening are rarely mentioned in other Gordius species. Free-living adults emerged and mated on wet soil under the forest canopy in the winter (late November to early February) at medium altitudes (1100–1700 m). Mucus-like structure covering on the body surface, which creates a rainbow-like reflection, might endow the worm with high tolerance to dehydration. Although Gordius chiashanussp. nov. seems to be more adaptive to the terrestrial environment than other horsehair worm species, cysts putatively identified as belonging to this hairworm species found in the aquatic paratenic host, Ephemera orientalis McLachlan, 1875, suggest the life cycle of Gordius chiashanussp. nov. could involve water and land. The free-living adults emerged from the definitive hosts might reproduce in the terrestrial environment or enter an aquatic habitat by moving or being washed away by heavy rain instead of manipulating the behavior of their terrestrial definitive hosts.

Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 3. Modelling

This is the third in a series of papers that investigate the semi-annual, annual and Universal Time variations in the magnetosphere. In this paper, we use the Lin et al. (2010) empirical model of magnetopause locations, along with the assumption of pressure equilibrium and the Newtonian approximation of magnetosheath pressure, to show that the equinoctial pattern arises in both the cross-tail current at the tail hinge point and in the total energy stored in the tail. The model allows us to study the effects of both dipole tilt and hemispheric asymmetries. As a test of the necessary assumptions made to enable this analysis, we also study simulations by the BATSRUS global MHD magnetosphere model. These also show that the reconnection voltage in the tail is greatest when the dipole tilt is small but this only applies at low solar wind dynamic pressurepSWand does not, on its own, explain why the equinoctial effect increases in amplitude with increasedpSW, as demonstrated by Paper 2. Instead, the effect is consistent with the dipole tilt effect on the energy stored in the tail around the reconnection X line. A key factor is that a smaller/larger fraction of the open polar cap flux threads the tail lobe in the hemisphere that is pointed toward/away from the Sun. The analysis using the empirical model uses approximations and so is not definitive; however, because the magnetopause locations in the two hemispheres were fitted separately in generating the model, it gives a unique insight into the effect of the very different offsets of the magnetic pole from the rotational pole in the two hemispheres. It is therefore significant that our analysis using the empirical model does predict aUTvariation that is highly consistent with that found in both transpolar voltage data and in geomagnetic activity.

A new species of Gordius (Phylum Nematomorpha) from terrestrial habitats in North America.

Freshwater hairworms (class Gordiida) are members of the phylum Nematomorpha that use terrestrial arthropods as definitive hosts but reside as free-living adult worms in rivers, lakes, or streams. The genus Gordius consists of 90 described species, of which three species were described from freshwater habitats in North America. In this paper we describe a new species of Gordius from terrestrial habitats in Oklahoma, Texas, and Louisiana, United States. Oddly, each year hundreds of adult free-living worms appear after bouts of heavy rain on streets, sidewalks, and lawns during the winter season, when terrestrial arthropod hosts are not active. The new species is described based on morphological characters of adults and non-adult stages including the egg strings, eggs, larvae, and cysts. Adult males have a unique row of bristles on the ventral inner side of each tail lobe and a circular pattern of bristles on the terminal end of each lobe, which distinguishes them from all other described North American species of Gordius. The egg string, larval, and cyst morphology of this new species conform to previous descriptions of non-adult hairworm stages for the genus Gordius. However, the eggs of this new species of hairworm are unique, as they contain an outer shell separated by distinct space from a thick inner membrane. The consistent occurrence of this gordiid in terrestrial habitats, along with its distinct egg morphology, suggests that this new species of hairworm has a terrestrial life cycle.