Ionospheric Plasma Transport and Loss in Auroral Downward Current Regions

A detailed study of the effects of auroral current systems on thermal ionospheric plasma transport and loss is conducted using a new ionospheric model. The mathematical formulation of the model is a variation on the 5‐moment approximation which describes the temporal evolution of density, drift, and temperature for five different ion species in two spatial dimensions. The fluid system is closed through a 2‐D electrostatic treatment of the auroral currents. This model is used to examine the interplay between ion heating, perpendicular transport, molecular ion generation, and type‐1 ion upflows in a self‐consistent way for the first time. Simulations confirm that the depletion of E‐region plasma due to current closure occurs on extremely fast time scales (5–30 s), and that it is dependent on current system scale size. Near the F‐region peak, the loss is mostly due to enhanced recombination from the conversion of the plasma to molecular ions. The F‐region loss process is fairly slow (120–300 s) by comparison to lower altitude processes and is highly electric field dependent. On similar time scales, transient ion upflows from frictional heating move plasma from the near topside ionosphere (∼500 km) to higher regions, leaving depletions and enhancing plasma densities at very high altitudes. Results indicate the existence of large molecular ion upflows near the F‐region peak and may shed some light on ionospheric source regions for outflowing molecular ions. Neutral atmospheric winds and densities are also shown to play an important role in modulating molecular ion densities, frictional heating, and currents

Dynamics of Density Cavities Generated by Frictional Heating: Formation, Distortion, and Instability

A simulation study of the generation and evolution of mesoscale density cavities in the polar ionosphere is conducted using a time-dependent, nonlinear, quasi-electrostatic model. The model demonstrates that density cavities, generated by frictional heating, can form in as little as 90 s due to strong electric fields of ∼120 mV/m, which are sometimes observed near auroral zone and polar cap arcs. Asymmetric density cavity features and strong plasma density gradients perpendicular to the geomagnetic field are naturally generated as a consequence of the strong convection and finite extent of the auroral feature. The walls of the auroral density cavities are shown to be susceptible to large-scale distortion and gradient-drift instability, hence indicating that arc-related regions of frictional heating may be a source of polar ionospheric density irregularities

Biochemistry of Transglutaminases and Cross-Linking in the Skin

Transglutaminase is a calcium-dependent enzyme found widely in nature. It catalyzes the formation of α-(γ-glutamyl)lysine bonds that participate in processes varying from fibrin clot formation to epidermal cell envelope formation. Epidermal transglutaminase is localized to the granular layer of the epidermis. It catalyzes the covalent cross-linking of a soluble cytoplasmic substrate into large polymers to form the cornified envelope that lines the inner membrane of keratinocytes in the stratum corneum, The soluble precursor from epidermis has been named keratolinin, and from keratinocyte culture, it has been named involucrin. Hair follicle transglutaminase is biochemically and immunochemically distinct from its epidermal counters part. It has been localized to the inner root sheath and medulla of the hair follicle, The substrate of hair follicle transglutaminase has been poorly defined but appears to be rich in the amino acid citrulline, Transglutaminase has been shown to be an important marker of normal differentiation. There is a rise in its activity at the time of keratinization, and transglutaminase activity has been shown to be greatly decreased in basal cell epithelioma and in psoriasis. Keratinocyte cell culture has proven most helpful in delineating the processes of normal differentiation and keratinization, since the formation of the cell envelope in culture appears to parallel the formation in vivo

Incoherent Scatter Radar Estimation of F Region Ionospheric Composition During Frictional Heating Events

A method is developed for estimating F region ion composition from incoherent scatter radar (ISR) measurements during times of frictional ion heating. The technique addresses ion temperature‐mass ambiguities in the IS spectra by self‐consistently modeling ion temperature profiles, including the effects of ion temperature anisotropies and altitude‐independent neutral winds. The modeled temperature profiles are used in a minimization procedure to estimate ion composition consistent with the recorded IS spectra. The proposed method is applicable to short‐integration (min) data sets from either single‐beam or multiple‐beam experiments. Application of the technique to Sondrestrom ISR measurements shows increases in F region molecular ions in response to frictional heating, a result consistent with previous theoretical and observational work. Estimates of ion composition are shown to be relatively insensitive to moderate variations in the neutral atmospheric model, which serves as input to the method. The technique developed in this work is uniquely qualified for studying highly variable ion composition near auroral arcs and associated processes such as molecular ion upflows. It also addresses a systematic source of error in standard ISR analysis methods when they are applied in such situations

Auroral Ionospheric F Region Density Cavity Formation and Evolution: MICA Campaign Results

Auroral ionospheric F region density depletions observed by PFISR (Poker Flat Incoherent Scatter Radar) during the MICA (Magnetosphere‐Ionosphere Coupling in the Alfvén Resonator) sounding rocket campaign are critically examined alongside complementary numerical simulations. Particular processes of interest include cavity formation due to intense frictional heating and Pedersen drifts, evolution in the presence of structured precipitation, and refilling due to impact ionization and downflows. Our analysis uses an ionospheric fluid model which solves conservation of mass, momentum, and energy equations for all major ionospheric species. These fluid equations are coupled to an electrostatic current continuity equation to self‐consistently describe auroral electric fields. Energetic electron precipitation inputs for the model are specified by inverting optical data, and electric field boundary conditions are obtained from direct PFISR measurements. Thus, the model is driven in as realistic a manner as possible. Both incoherent scatter radar (ISR) data and simulations indicate that the conversion of the F region plasma to molecular ions and subsequent recombination is the dominant process contributing to the formation of the observed cavities, all of which occur in conjunction with electric fields exceeding ∼90 mV/m. Furthermore, the cavities often persist several minutes past the point when the frictional heating stops. Impact ionization and field‐aligned plasma flows modulate the cavity depth in a significant way but are of secondary importance to the molecular generation process. Informal comparisons of the ISR density and temperature fits to the model verify that the simulations reproduce most of the observed cavity features to a reasonable level of detail

Measuring the Seeds of Ion Outflow: Auroral Sounding Rocket Observations of Low-Altitude Ion Heating and Circulation

We present an analysis of in situ measurements from the MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) nightside auroral sounding rocket with comparisons to a multifluid ionospheric model. MICA made observations at altitudes below 325 km of the thermal ion kinetic particle distributions that are the origins of ion outflow. Late flight, in the vicinity of an auroral arc, we observe frictional processes controlling the ion temperature. Upflow of these cold ions is attributed to either the ambipolar field resulting from the heated electrons or possibly to ion-neutral collisions. We measure convection away from the arc (poleward) and downflows of hundreds of m s−1 poleward of this arc, indicating small-scale low-altitude plasma circulation. In the early flight we observe DC electromagnetic Poynting flux and associated ELF wave activity influencing the thermal ion temperature in regions of Alfvénic aurora. We observe enhanced, anisotropic ion temperatures which we conjecture are caused by transverse heating by wave-particle interactions (WPI) even at these low altitudes. Throughout this region we observe several hundred m s−1 upflow of the bulk thermal ions colocated with WPI; however, the mirror force is negligible at these low energies; thus, the upflow is attributed to ambipolar fields (or possibly neutral upwelling drivers). The low-altitude MICA observations serve to inform future ionospheric modeling and simulations of (a) the need to consider the effects of heating by WPI at altitudes lower than previously considered viable and (b) the occurrence of structured and localized upflows/downflows below where higher-altitude heating rocesses are expected

Transient Ionospheric Upflow Driven by Poleward Moving Auroral forms Observed During the Rocket Experiment for Neutral Upwelling 2 (RENU2) Campaign

This study examines cumulative effects of a series of poleward moving auroral forms on ion upflow and downflow. These effects are investigated using an ionospheric model with inputs derived from the Rocket Experiment for Neutral Upwelling 2 (RENU2) sounding rocket campaign. Auroral precipitation inputs are constrained by all‐sky imager brightness values resulting in significant latitudinal structuring in simulated ionospheric upflows due to transient forcing. For contrast, a case with steady forcing generates almost double the O+ upflow transport through 1,000 km when compared to poleward moving auroral form‐like structures. At high altitudes, model results show a spread in upflow response time dependent on ion mass, with molecular ions responding slower than atomic ions by several minutes. While the modeled auroral precipitation is not strong enough to accelerate ions to escape velocities, source populations available for higher‐altitude energization processes are greatly impacted by variable forcing exhibited by the RENU2 event.Key PointsImager data provide realistic transient forcing constraints for model inputs to simulate observations from a high‐latitude rocket flightTransient forcing deposits energy over a wider latitudinal region but less energy in any specific locationModeling a sequence of poleward moving auroral forms with realistic spatiotemporal variability generates significant latitudinal structuringPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150562/1/grl59002.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150562/2/grl59002-sup-0001-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150562/3/grl59002_am.pd

Reproductive period and preclinical cerebrospinal fluid markers for Alzheimer disease: a 25-year study

OBJECTIVE: The aim of the study was to examine the association between reproductive period, as an indicator of endogenous estrogen, and levels of cerebrospinal fluid (CSF) biomarkers for Alzheimer disease (AD). METHODS: A population-based sample of women from Gothenburg, Sweden was followed from 1968 to 1994 (N = 75). All women had natural menopause and were free from dementia. Information on reproductive period (age at menarche to age at menopause) was obtained from interviews from 1968 to 1980. Lumbar puncture was performed from 1992 to 1994 and CSF levels of Aβ42, Aβ40, P-tau, and T-tau were measured with immunochemical methods. Linear regression models adjusted for potential confounders were used to analyze the relationship between reproductive period and CSF biomarkers for AD. RESULTS: Longer reproductive period was associated with lower levels of Aβ42 (β = -19.2, P  = 0.01), higher levels of P-tau (β = 0.03, P  = 0.01), and lower ratio of Aβ42/Aβ40 (β = -0.02, P  = 0.01), while no association was observed for T-tau (β = 0.01, P  = 0.46). In separate analyses, examining the different components of reproductive period, earlier age at menarche was associated higher levels of P-tau (β = -0.07, P  = 0.031) and lower ratio of Aβ42/Aβ40 (β = 0.05, P  = 0.021), whereas no association was observed with Aβ42 (β = 31.1, P  = 0.11) and T-tau (β = -0.001, P  = 0.98). Furthermore, no association was observed between age at menopause and CSF biomarkers for AD. CONCLUSIONS: Our findings suggest that longer exposure to endogenous estrogen may be associated with increased levels of AD biomarkers in the preclinical phase of AD. These findings, however, need to be confirmed in larger samples. / Video Summary: http://links.lww.com/MENO/A804