A multifrequency (ten spectral lines between VHF and S band) coherent radio beacon is presently transmitting continuously from a 1000‐km, high‐inclination orbit for the purpose of characterizing the transionospheric communication channel. Its high phase‐reference frequency (2891 MHz) permits direct observation of complex‐signal scintillation, and its very stable, sun‐synchronous orbit allows repeated pre‐midnight observations at low latitudes and near‐midnight observations at auroral latitudes. We present here early results of the observations; salient points include the following. First, most of the data are consistent with phase‐screen modeling of the production of ionospheric scintillation, including an ƒ−2 frequency dependence for phase variance. Second, propagation theories invoking weak, single scatter seldom are adequate, because even moderate intensity scintillation usually is accompanied by phase fluctuations comparable to or greater than a radian. Third, under conditions producing GHz scintillation (near the geomagnetic equator), lower frequencies show marked diffraction effects, including breakdown of the simple ƒ−2 behavior of phase variance and loss of signal coherenceacross a band as narrow as 11.5 MHz at UHF.

Nighttime multifrequency scintillation and 50-MHz radar backscatter observations simultaneously performed over a nearly common ionospheric volume at the dip equator in Peru during March 1977 were used to study the relationship between the large-scale irregularities (-•0.1-1 km) giving rise to scintillations and small-scale irregularities (3 m) causing 50-MHz backscatter. It is shown that during the generation phase of equatorial irregularities in the evening hours, the kilometer-and meter-scale irregularities coexist, whereas in the later phase, approximately an hour after the onset, the meter-scale irregularities decay but the large-scale ones continue to retain their high spectral intensities. Further, multistation scintillation observations from a host of geostationary satellites as well as from the Wideband satellite indicate that eastward-drifting irregularity structures detected around midnight cause significant scintillations at UHF and L band but generally fail to give rise to appreciable backscatter. Thus, contrary to expectations, it is possible to have even L band scintillations without any plume structure on backscatter maps. This indicates that at later local time a cutoff of the spectral intensity probably occurs at some scale length between 100 and 3 m. These observational results are discussed in the context of current theories of plasma instability in the equatorial ionosphere.• Emmanuel Col}ege, Boston, Massachusetts 02115. •' Air Force Geophysics Laboratory, Hanscom Air Force Base, Bedford, M assach usetts 01731.

Recent analyses of auroral‐zone spaced‐receiver measurements have shown that the regions where sheetlike irregularities occur are confined to the equatorward portion of the nighttime scintillation zone where the westward and eastward electrojets flow. Poleward of this region, the irregularities are rodlike. For satellites in highly eccentric orbits, the spaced‐receiver technique can be used to measure ionospheric drifts. Simultaneous incoherent‐scatter radar measurements have revealed two types of F region ionization enhancements that are believed to be the source regions of persistent scintillation features on polar satellite transmissions. One type is found at the equatorward edge of the diffuse aurora and can persist for more than 10 hours. More dynamic structures often occur in pairs, which suggests an association with ‘inverted‐V’ precipitation events. Radar data have also revealed large‐scale east‐west structure in the poleward enhancements.

Funded by the NSF CubeSat and NASA ELaNa programs, the Dynamic Ionosphere CubeSat Experiment (DICE) mission consists of two 1.5U CubeSats which were launched into an eccentric low Earth orbit on October 28, 2011. Each identical spacecraft carries two Langmuir probes to measure ionospheric in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a science grade magnetometer to measure in-situ DC and AC magnetic fields. Given the tight integration of these multiple sensors with the CubeSat platforms, each of the DICE spacecraft is effectively a "sensorsat" capable of comprehensive ionospheric diagnostics. The use of two identical sensor-sats at slightly different orbiting velocities in nearly identical orbits permits the de-convolution of spatial and temporal ambiguities in the observations of the ionosphere from a moving platform. In addition to demonstrating nanosat-based constellation science, the DICE mission is advancing a number of groundbreaking CubeSat technologies including miniaturized mechanisms and high-speed downlink communications.