RSS 1.0Geophysical Institute
At the Geophysical Institute the diversity of our research focus is reflected by our disciplinary-based, functional groupings of faculty and research staff. These divisions are: space physics and aeronomy, atmospheric sciences, snow, ice, and permafrost, seismology, volcanology, and tectonics and sedimentation. Along with an ubiquitous, cross-discipline remote sensing group, these research divisions reflect the range and diversity of the active scientific research projects which reach from the center of the sun to the center of the earth and beyond.
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Alaska Earthquake Center
Advancing Alaska's resilience to earthquakes through monitoring, research and public engagement -
Atmospheric Sciences
The atmospheric sciences group advances understanding of the physical, chemical and dynamical processes of the atmosphere with a focus on polar regions.
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Recent Submissions
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Alaska Earthquake Center Quarterly Technical Report October-December 2024This series of technical quarterly reports from the Alaska Earthquake Center (AEC) includes detailed summaries and updates on Alaska seismicity, the AEC seismic network and stations, fieldwork, our online presence, public outreach, and lists publications and presentations by AEC staff. Multiple AEC staff members contributed to this report.
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2024 Alaska Seismicity SummaryThe Alaska Earthquake Center reported 39,836 seismic events in Alaska and neighboring regions in 2024. The largest earthquakes were two magnitude 6.3 events that were part of a swarm of M6 events on December 8-9 in the Andreanof Islands region of Alaska. The first occurred on December 8 at 19:57:07 UTC, and the second occurred at 00:15:30 on December 9, followed by an M6.1 23 minutes later. Other strong earthquakes include two M6.0 events, one on May 19 and one on July 19, both south of Yunaska Island in the Islands of Four Mountains region of the Aleutians, and the strongest mainland earthquake, an M5.9, off the coast of Port Alexander in Southeast Alaska on January 12. We continued to monitor the 2020 M7.8 Simeonof sequence, but all other previous sequences and swarms have dropped below one event per day and are no longer being tracked. Numerous short-lived swarms occurred in 2024 and will be discussed below.
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Radiowave scattering structure in the disturbed auroral ionosphere : some measured propertiesA technique for quantitative description of radiowave scattering structure in the disturbed auroral ionosphere is developed in this work. Application is made by means of multi-spacing interferometric observations of a radio star. The work is based on the observed fact that sufficient scattering causes a measurable decrease in correlation of output voltages from neighboring antennas. Such correlation decreases are called visibility fades herein and have been called long-duration fades and radio-star fadeouts by other workers. Random noise theory is employed, and it is assumed that the angular spectrum of the source, as received at the ground after scattering, is randomly phased. However, the usual assumption of a Gaussian autocorrelation function to describe the scattering structure is circumvented, and provision is made for the existence of quasi-periodic structure. Further, the usual assumption of weak (single) or strong (multiple) scatter is avoided. The statistical characteristics of amplitude, phase, and complex signal are developed for the general case of arbitrary degree of scatter, using a numerical method. The technique is applied to observations with phase-switch and phase-sweep interferometers, yielding two important parameters of the received wavefront, the coherence ratio and the wavefront auto-correlation function. The coherence ratio is defined as the ratio of nonscattered to scattered flux received from the source. The wavefront autocorrelation function is defined as the spatial autocorrelation function of the scattered portion of the (complex) wavefront. Two quantities which describe the ionospheric scattering region are obtained from the coherence ratio and wavefront autocorrelation function. First, the optical depth of the region (considered as a purely scattering medium) is determined from the coherence ratio. Second, the ionospheric structural autocorrelation function is established jointly from the wavefront autocorrelation function and the optical depth, yielding a statistical description of the average size and idealized shape of the ion-density irregularities which produced the scattering. Forty-nine visibility fades observed at College, Alaska, between November of 1964 and February of 1966, inclusive, are analyzed. A majority of the fades revealed optical depths in excess of unity at 68 MHz. Optical depth is numerically equal to mean-square fluctuation in radio-frequency phase across a plane at the base of the scattering region, so the fades were characterized by rms phase deviations in excess of one radian at 68 MHz. An approximately inverse-square dependence of optical depth on frequency was obtained from simultaneous observations at 68, 137, and 223 MHz. At 68 MHz, tri-spacing observations were carried out on east-west baselines of 110 meters (25 λ), 220 meters (50 λ), and 330 meters (75 λ). The observations seldom were consistent with the demands of a Gaussian autocorrelation function, as is commonly assumed. Rather, the disturbed auroral ionosphere displays evidence of quasi-periodic structure in the dimensional range of tens and hundreds of meters. The structure observed is comparable in size to auroral rays. While most of the observations were consistent with the assumption of a randomly phased angular spectrum, a significant minority was not. Quantitative results could not be obtained in these instances, and they imply the existence of highly developed quasi-periodicity. Theoretical work is needed to bridge the gap between quasi-periodic structure in the sense of random-noise theory and strict periodicity. Narrow-beam photometers were mounted on one of the interferometer antennas tracking the radio star. Auroral luminosity was recorded along the line of sight during 100% of the visibility fades which occurred at night under clear-sky conditions and during many night-time fades which occurred under cloudy conditions Thus, VHF radio-star visibility fades in the auroral zone result from scattering by irregularities directly associated with auroral forms, at least at night.
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An investigation of solar induced phenomena at magnetically conjugate pointsThe results of a comprehensive study of solar induced geophysical phenomena at pairs of stations linked by a magnetic field line are presented. Studies have established that magnetic variations (except Sq), telluric currents, ionospheric absorption, visual auroras, VLF and ELF emissions and auroral X-rays occur in similar manner in conjugate areas—in time, form and amplitude. The variations of the magnetic field were the most thoroughly studied phenomena. It was found that auroral zone electrojets occur in conjugate patterns, and that a conjugate area, elongated in geomagnetic latitude, can be defined by comparisons of magnetic records. This conjugate area appears to move in time, as the electrojets depart somewhat from conjugate patterns. The magnetic variations at mid and low latitude due to the return current paths of the electrojets are conjugate to approximately the same degree as the ‘primary’ auroral zone activity. At very high latitudes there is a diurnal variation in the degree of correlation at conjugate points—probably due to the distortion of the magnetic field by the solar wind. Some evidence is presented for two kinds of very high latitude magnetic disturbance. One occurring on the night side is probably due to the poleward expansion of auroral electrojet systems. The other occurs on the day side, even on very quiet days, and is possibly due to hydromagnetic waves, produced by the interaction of the magnetosphere surface and the solar wind. This dayside agitation shows inferior correlation. The Sq variation was investigated and found to be a non-conjugate phenomenon. The theoretical effects of field line linkage are found to skew rather than to equalize the variations from a conjugate pattern. The close relationship of telluric currents to magnetic variations, and the effects of local conductivity are considered. Comparison of records from paired stations confirm that telluric currents are conjugate. The mechanism of short period (~ 1 minute) oscillations may be found in modes of oscillation of the magnetosphere, as apart from ionospheric current systems. A pronounced diurnal variation was found in the power spectra and the polarization of short period oscillations at a mid-latitude pair. Comparisons of all-sky camera data from several conjugate pairs confirm that auroras occur in similar, simultaneous displays in conjugate areas. Occasional differences between the northern and southern displays were observed, similar to the anomalies in the magnetic variations. An attempt was made to study the conjugacy of radio auroras at 50-55 Mc/s but the results were inconclusive. Ionospheric absorption of cosmic radio noise—a phenomenon closely related to influx of charged particles and X-rays—has been shown in several studies to occur as a conjugate phenomenon. A conjugate area, similar in shape to that defined by correlation of magnetic variations was found for absorption events. Although no new work was carried out, the published results of conjugate studies of VLF (whistlers, etc.), ELF (micropulsations) and auroral zone balloon flights (auroral zone X-rays) are presented and discussed.
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Alaska Earthquake Center Quarterly Technical Report July-September 2024This series of technical quarterly reports from the Alaska Earthquake Center (AEC) includes detailed summaries and updates on Alaska seismicity, the AEC seismic network and stations, fieldwork, our online presence, and lists publications and presentations by AEC staff. Multiple AEC staff members contribute to this report. It is issued within 1-2 months after the completion of each quarter Q1: January-March, Q2: April-June, Q3: July-September, and Q4: October-December. The first report was published for January-March, 2021.
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Dynamo action in the ionosphere and motions of the magnetospheric plasmaThis thesis presents a study of the dynamic interaction which takes place between the magnetospheric plasma and the underlying neutral atmosphere; it is hoped thus to gain a better understanding of the effects of this interaction upon the steady state configuration of the magnetosphere. The neutral portion of the atmosphere (the neutrosphere) and the overlying ionized regions (the upper atmosphere and magnetosphere) may be regarded as two distinct dynamic domains that interact in a region of transition occurring between 100 and 150 km over the earth. The neutrosphere because of its greater mass will dominate the motion, and the magnetospheric plasma can be expected to undergo motions related to those of the upper neutrosphere and transition region. However, the geomagnetic field restricts the motion of the magnetospheric plasma to a particular class, allowing one to consider the magnetospheric motion to be constrained. Motions in the transition region of the class not permitted the magnetospheric plasma will give rise to forces against the constraint. The reaction of the constraint on the atmosphere of the transition region takes the form of a Lorentz force J x B where J is the current responsible for the well known solar quiet day daily magnetic variation (Sq). The explanation for the production of this current in the transition region has traditionally been presented in terms of a dynamo-like electromotive force generated by motions of the conducting atmosphere through the magnetic field, whence the transition region is aptly named the dynamo region. The Lorentz force represented by this current constitutes a significant term in the equation of motion for the dynamo region. Another important term arises from eddy viscous stresses immediately below the dynamo region. The equation of motion for the dynamo region must thus include such forces as well as the pressure gradient and Coriolis terms. However, our almost total ignorance of the eddy viscous stress field at the lower surface of the dynamo layer at present precludes our deducing the entire dynamo layer winds from the observed Sq magnetic variation. The kinematics of the dynamo layer are discussed and the motion or the dynamo layer is divided into a symmetric and an antisymmetric part. The term symmetric is here used to describe winds in the northern and southern hemisphere that are the mirror images of each other with respect to the equatorial plane. It is demonstrated that the symmetric component gives rise to electrostatic fields transverse to the field lines, but to no currents along the field lines, while the antisymmetric case produces the converse effects. The symmetric and antisymmetric winds are further divided into components according to the horizontal electromotive force they produce. (a) Symmetric Wind. In the case of the symmetric wind, only the portion of the wind producing the solenoidal component of the horizontal dynamo electromotive force is effective in producing ionospheric currents. It is demonstrated that only this current producing wind system acts against the constraints imposed by the geomagnetic field on magnetospheric motions. The motion of the magnetospheric plasma driven by each such wind system is discussed. The earlier treatments of the dynamo theory consider the dynamo region to be a single layer in which the wind system and the electric conductivity are assumed to be uniform in height. A new, more general derivation of the layer's dynamo action is given in which no restrictions are placed upon the vertical distributions. An effective wind is defined which permits the use of the earlier equations relating the current function, the electrostatic field, and the scalar field describing the current producing part of the effective wind. The equation relating the electrostatic field and the current function is essentially that employed by Maeda (1956), allowing his solution for the portion of the electrostatic field associated with the current producing wind to remain unaffected by the stratification of the wind system. Mathematical techniques for solving the dynamo equations for the electrostatic field are developed. These allow for a quite general conductivity distribution over the globe, only requiring that it be expressible in surface harmonics. The effect of undetected zonal currents upon the solution for the electrostatic field is discussed. It is suggested that a considerable diurnal component of electrostatic field and other components as well may be hidden from us by our inability to detect the prevailing magnetic perturbations produced by zonal currents. The electrostatic field associated with the non-current producing components of the symmetric wind is likewise hidden from us. (b) Antisymmetric Wind. The equations for the current driven by the antisymmetric component of wind are derived, and some of the effects of such currents are discussed. It is found that the conduction of current along the field lines from one hemisphere to the other is associated with an interhemispheric stress between geomagnetically conjugate points of order 3 x 10⁻⁷ newtons/meter². In addition it is found that an antisymmetric layer current density of 5 amperes/km into the polar cap region (across the 75° latitude circle) might give rise to a displacement of about 150 km in the relative position of the conjugate points defined by field lines of the magnetospheric tail. It is suggested that the dynamo action in the 100 to 150 km height plays a role in determining the manner in which the magnetosphere divides itself into the corotating region and the magnetospheric tail.
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Improved contrail forecasting techniques for the subarctic setting of Fairbanks, AlaskaJet contrails can be frequently observed in the subarctic setting of Fairbanks, Alaska, much like in the contiguous United States. Since March of 2000, continuous digital imagery of the sky was obtained, supported by FAA flight data and radiosonde ascents at the Fairbanks International Airport. There were a total of 2504 over-flights (March 2000-July 2002) at Fairbanks, but for a great number of these, contrail observations were not possible due to clouds and/or darkness. For 590 cases, the formation of contrails could be confirmed; their life span varied widely from a few seconds to several hours. In general, cold temperatures and high relative humidity at flight level favored the formation of contrails. These conditions are frequently found in the upper troposphere close to the tropopause. Using our substantial database, different existing algorithms were tested and, in part, improved in order to predict contrail formation and lifetime. The best results were obtained with an algorithm described by Schumann (1996) and an aircraft specific contrail factor of 0.036 g/kgK. For contrails within 4 hours of the radiosonde ascents, a combined hit rate for correctly forecasting the occurrence and non-occurrence of contrails of 92% was obtained.
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Maritime Guidance for Distant and Local Source Tsunami Events: Chenega Bay, AlaskaThese documents provide response guidance for Chenega Bay in the event of tsunamis for small vessels such as recreational sailing and motor vessels, and commercial fishing vessels. The developed documents follow the guidance developed by the National Tsunami Hazard Mitigation Program (NTHMP) and are based on anticipated effects of a maximum-considered distant and locally generated tsunami event.
