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Types Pc 1-2 and IPDP micropulsations at the auroral zoneA micropulsation recording program was carried out at College and Anchorage, Alaska and at Bar I, Canada, with induction magnetometers. The analysis program centered mainly on synoptic and polarization characteristic for types Pc 1-2, IPDP, and Pi burst micropulsation events. Summaries of the known morphological features for structured Pc 1 and unstructured Pc 1-2 micropulsations are given. The synoptic studies disclosed latitude relationships between unstructured Pc 1-2, IPDP, and Pi burst events. At the onset of a polar substorm, Pi bursts occur near midnight at 65°-70° geomagnetic latitudes. IPDP events follow the Pi burst and are seen in evening hours at 60°-65° latitudes. IPDP events seen in afternoon hours are often preceded by unstructured Pc 1-2 activity which maximizes a few degrees polewards of the IPDP. The IPDP events are seen in the evening “bulge” region of the plasmasphere. The proton plasma requirement for IPDP wave generation suggests that protons which are injected near midnight in the Pi burst event drift westwards into the bulge and generate unstructured Pc 1-2 and IPDPs there. The polarization characteristics of Pc 1 activity indicate that simple structured Pc 1 events originate on a stable tube of force. Unstructured Pc 1 events and events which are superpositions of several events usually display pronounced time-variability in the polarization characteristics.
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Computed HF auroral backscatter traces for various distancesComputed ionospheric backscatter traces in the HF portion of the radio spectrum are illustrated for a number of distances between the auroral belt and the observing radar. The type, frequency range, and observed scattering height of HF auroral backscatter traces are strongly dependent upon the ionospheric propagation conditions existing between the auroral belt and the observer. Backscatter echoes produced in a given region of space by a single backscattering mechanism can have completely different range versus frequency characteristics when observed at sites located at different distances from the scattering region. Even though a given bank of auroral-belt irregularities extends through both the E and F regions, it is possible that only E-scatter is detected at one distance, and F-scatter at another. Trace type, scattering height, and frequency range of the observed backscatter echoes are strongly dependent upon the distance between the auroral belt and the observer.
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The relationship between submarine melt and subglacial discharge from observations at a tidewater glacierAt tidewater glacier termini, ocean-glacier interactions hinge on two sources of freshwater—submarine melt and subglacial discharge—yet these freshwater fluxes are often unconstrained in their magnitude, seasonality, and relationship. With measurements of ocean velocity, temperature and salinity, fjord budgets can be evaluated to partition the freshwater flux into submarine melt and subglacial discharge. We apply these methods to calculate the freshwater fluxes at LeConte Glacier, Alaska, across a wide range of oceanic and atmospheric conditions during six surveys in 2016–2018. We compare these ocean-derived fluxes with an estimate of subglacial discharge from a surface mass balance model and with estimates of submarine melt from multibeam sonar and autonomous kayaks, finding relatively good agreement between these independent estimates. Across spring, summer, and fall, the relationship between subglacial discharge and submarine melt follows a scaling law predicted by standard theory (melt ∼ discharge1/3), although the total magnitude of melt is an order of magnitude larger than theoretical estimates. Subglacial discharge is the dominant driver of variability in melt, while the dependence of melt on fjord properties is not discernible. A comparison of oceanic budgets with glacier records indicates that submarine melt removes 33%–49% of the ice flux into the terminus across spring, summer, and fall periods. Thus, melt is a significant component of the glacier's mass balance, and we find that melt correlates with seasonal retreat; however, melt does not appear to directly amplify calving.
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The preliminary analysis of IGY magnetic results from Alaskan observatoriesA preliminary analysis has been made of the magnetic data from the IGY network stations in Alaska. A few examples of magnetic bays were selected, and the distribution of electric current responsible for them was studied with a simple model for the current system, namely, line, or sheet, currents. The records obtained by the differential magnetometer were analyzed and compared with the gradient of the magnetic elements computed from the regular magnetograms taken at neighboring stations. The differential records were found not in agreement with the latter computed values. The discrepancy is probably due to local electric currents induced in the ground. A suggestion is made for future work on the auroral electrojets.
