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This paper describes a new method for remote sensing of magnetic field fluctuations at ionospheric altitudes using a relatively long‐baseline interferometer and exceptionally bright cosmic radio sources at 35 MHz. The technique uses sensitive measurements of the difference in phase between two phased array telescopes separated by about 75 km and between the right and left circular polarizations to measure the amount of differential Faraday rotation. Combined with estimates of the background magnetic field and total electron content, these can be converted to measurements of fluctuations in the differential magnetic field parallel to the line of sight, ΔB_‖. The temporal gradient in ΔB_‖roughly follows the diurnal pattern expected for B_‖due to the vertical gradient in the background electric field, but at roughly 25% the magnitude and offset by ∼50 nT hr⁻¹. This suggests that the diurnal variation in the electric fields observed by the two telescopes are similar but slightly different (|ΔE| ≲ 0.1 mV m⁻¹). Fluctuations in ΔB_‖were typically ∼10–30 nT with wavelike fluctuations often apparent. These typically have oscillation periods of about 10–30 min, similar to traveling ionospheric disturbances (TIDs). Simultaneous observations toward two sources separated by 25.4° on the sky (∼140 km in the F‐region) show a few detections of wavelike disturbances with lags of ±10–30 min between them. These imply speeds on the order of 100–200 m s⁻¹, also similar to TIDs. We estimate that gravity waves with amplitudes within the dynamo region of ∼10 m s⁻¹could generate the observed fluctuations in ΔB_‖.

The Deployable Low‐Band Ionosphere and Transient Experiment (DLITE) is a four‐element interferometric radio telescope made from mostly commercial off‐the‐shelf parts to minimize costs and maximize ease of deployment. It operates in the high frequency and very high frequency (VHF) regimes, nominally in a 30–40 MHz band, but with good sensitivity (sky‐noise dominated) in the 20–80 MHz range. Its configuration is optimized to probe ionospheric structure using the so‐called “A‐Team,” exceptionally bright sources of cosmic radio emission. Methods have been developed to track the apparent positions and intensities of A‐Team sources without the need for beam forming to enable measurements of VHF scintillations as well as total electron content gradients. Time difference of arrival and frequency difference of arrival methods have been adapted for all‐sky imaging to facilitate both statistical measurements of scintillation levels and time domain astronomy. This study provides a detailed description of the system design, the analysis algorithms, and the science that can be conducted using results from two prototype DLITE systems in Maryland and New Mexico.