Secular variation of activity in comets 2P/Encke and 9P/Tempel 1

We compare production rates of H20 derived from International Ultraviolet Explorer (IUE) spectra from multiple apparitions of 2 comets, 2P/Encke and 9P/Tempel 1, whose orbits are in near-resonance with that of the Earth. Since model-induced errors are primarily a function of observing geometry, the close geometrical matches afforded by the resonance condition results in the cancellation of such errors when taking ratios of production rates. Giving careful attention to the variation of model parameters with solar activity, we find marginal evidence of change in 2P/Encke: a 1-sigma pre-perihelion decrease averaging 4%/revolution over 4 apparitions from 1980-1994, and a 1-sigma post-perihelion increase of 16%/revolution for 2 successive apparitions in 1984 and 1987. We find for 9P/Tempel 1, however, a 7-sigma decrease of 29%/revolution over 3 apparitions from 1983-1994, even after correcting for a tracking problem which made the fluxes systematically low. We speculate on a possible association of the character of long-term brightness variations with physical properties of the nucleus, and discuss implications for future research

Horizontal Ionospheric Electron Density Gradients Observed by FORMOSAT-3/COSMIC TIP: Spatial Distributions and Effects on VLF Wave Propagation at Mid-Latitudes

We investigate the spatial variability of electron densities in the nightside ionosphere and its effects on very-low frequency (VLF) wave propagation using a suite of instruments from the FORMOSAT-3/Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) spacecraft.We use observations from the Tiny Ionospheric Photometer (TIP) instruments to infer the horizontal electron density gradients along each satellite track. We demonstrate that the OI 1356 _ radiance measured by the TIP instruments tracks the horizontal electron density structure well with high spatial resolution and unprecedented sensitivity. Accurate measurements of the horizontal electron density gradients are important for improving retrieved electron density profiles from GPS occultation and other tomographic remote sensing techniques. The processes underlying the variability in the large-scale, nightside electron density gradients are the main drivers of ionospheric weather. TIP observations reveal significant variability in both the small and large scale structure of the nightside ionosphere. The relative intensities, relative widths, and latitudinal separation of the northern and southern ionization crests of the Appleton anomalies show a high degree of longitudinal variation.We demonstrate how the TIP observations can be used to measure the horizontal gradient of the refractive index of whistler-mode VLF waves propagating in a cold, collisionless plasma. These measurements are critical for understanding how gradients in electron density associated with ionospheric structure such as depletions and the Appleton anomalies affect VLF wave propagation through the equatorial and mid-latitude ionosphere

CIRCE: Coordinated Ionospheric Reconstruction Cubesat Experiment

The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) is a collaborative space mission between the UK Defence Science and Technology Laboratory (Dstl), and the US Naval Research Laboratory (NRL) in developing small satellite ionospheric physics capability. CIRCE will characterise space weather effects on a regional scale in the ionosphere/thermosphere system. Properly characterising the dynamic ionosphere is important for a wide range of both civil and defence applications such as GPS, communications, and sensing technology. Consisting of two near-identical 6U (2x3U) CubeSat buses, the CIRCE nanosatellites will fly in a lead-follow tandem configuration in co-planar near-polar orbits at 500km altitude. Provided by Blue Canyon Technologies (BCT), the two buses will use differential drag to achieve and maintain an in-track separation of between 250 and 500km, allowing short time-scale dynamics to be observed in-situ. These nanosatellites each carry a complement of 5 individual scientific instruments, contributed from academic, industrial, and government partners across the UK and US. Scheduled to launch in 2021 via the US Department of Defence Space Test Program, the two CIRCE satellites will provide observations to enable a greater understanding of the driving processes of geophysical phenomena in the ionosphere/thermosphere system, distributed across a wide range of latitudes, and altitudes, as the mission progresses

Tomographic Reconstruction of the Low-Latitude Nighttime Electron Density Using FORMOSAT-3/COMSIC Radio Occultation and UV Photometer Data

The Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) is a constellation of six microsatellites that was launched into low-Earth orbit on 14 April 2006. Each FORMOSAT-3/COSMIC satellite contains a GPS Occultation Experiment (GOX) GPS receiver and a Tiny Ionospheric Photometer (TIP), which measure the ionosphere. In previous papers of Dymond and Thomas (2001) and Dymond et al. (2000), an algorithm for tomographically inverting GPS occultation and UV radiometer measurements has been presented. We apply this algorithm to the inversion of recently acquired FORMOSAT-3/COSMIC data and present the results

Observations of the Ionosphere Using the Tiny Ionospheric Photometer

The Tiny Ionospheric Photometer (TIP) on the Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) characterizes the nighttime ionosphere using 135.6-nm radiative recombination emission. TIP measures horizontal structure of the ionosphere with high precision and high spatial resolution. Latitudinal, longitudinal, and temporal distribution of the nighttime ionosphere is specified.We present a review of ionospheric observations made with TIP during the first five months of operation. Comparisons are made with other ionospheric sensors in order to validate the TIP observations and to demonstrate TIP resolution and sensitivity performance. Equatorial anomalies observed by TIP are compared with estimates of the E ___nB vertical drift during the post-sunset pre-reversal enhancement in the Peruvian sector. Low latitude irregularity structures observed by TIP are compared with measurements from ground-based sensors including: imaging photometers, ionosonde, and UHF scintillation receivers. Detailed measurements of low latitude density depletion depth and width are provided. Global ionospheric morphology observed by TIP is compared with similar observations by COSMIC radio occultation, and the GAIM model. The complexity of the underlying neutral winds is revealed by the TIP ionospheric morphology

Ionospheric Electron Density Concurrently Derived by TIP and GOX of FORMOSAT-3/COSMIC

The tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) onboard FORMOSAT-3/COSMIC (F3/C) are employed to measure the OI 135.6 nm intensities in the nadir direction and the total electron content (TEC) between the F3/C and GPS satellite in the ionosphere, respectively. Due to its very high sensitivity ~600 counts/Rayleigh and rather narrow nadir pointing 3.8___ncircular field-of-view, the TIP provides accurate characterization of ionospheric electron density gradients in the horizontal direction. Meanwhile, a technique of the low earth orbit (LEO) tomography is applied to analyze theGOX data obtaining the 3D distribution of ionosphere electron density. Here, we combine the two observations to carry out the LEO-TIP tomographic inversions, and demonstrate that the peak electron density (NmF2) retrieved from the TIP combined together with the peak altitude (hmF2) information from the LEO tomography profiles provides more realistic electron density

Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE),

The UK’s Defence Science and Technology Laboratory (Dstl) is partnering with the US Naval Research Laboratory (NRL) on a joint mission to launch miniature sensors that will advance space weather measurement and modelling capabilities. The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) comprises two 6U cube-satellites that will be launched into a near-polar low earth orbit (LEO), targeting 500 km altitude, in 2021. The UK contribution to CIRCE is the In situ and Remote Ionospheric Sensing (IRIS) suite, complementary to NRL sensors, and comprising three highly miniaturised payloads provided to Dstl by University College London (UCL), University of Bath, and University of Surrey/Surrey Satellite Technology Ltd (SSTL). One IRIS suite will be flown on each satellite, and incorporates an ion/neutral mass spectrometer, a tri-band global positioning system (GPS) receiver for ionospheric remote sensing, and a radiation environment monitor. From the US, NRL have provided two 1U Triple Tiny Ionospheric Photometers (Tri-TIPs) on each satellite (Nicholas et al., 201