[1] A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of nonmigrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped far below the peak in ionospheric density. The observations can be explained by consideration of the dynamo interaction of the tides with the lower ionosphere (E-layer) in daytime. The influence of persistent tropical rainstorms is therefore an important new consideration for space weather.

[1] The Far Ultraviolet Imager (FUV) on board the IMAGE satellite provides an instantaneous global view of the OI 135.6-nm nightglow with 2 min time resolution. Because the OI 135.6-nm emission from the nighttime ionosphere is determined by the line-of-sight integrated plasma density, the nightglow images are useful for studying the nighttime low-latitude ionosphere globally. With the IMAGE/FUV 135.6-nm observations from March to June 2002, we have examined the global characteristics of the nighttime equatorial anomaly (EA) by constructing a constant local time map (LT map), in which pixels within an assigned local time range are extracted from the IMAGE/FUV nightglow images obtained over an observation period of 3 days or more and are put together to compose a global distribution map of emission intensities at that local time. These LT maps show that the development of the EA has a significant longitudinal structure, in which peaks and dips of the crest emission intensity and the crest latitude have about 90°longitudinal separation in the longitude range from 0°to 250°. Although there is not enough data over the American sector, this result suggests that the EA longitudinal structure has a prominent zonal component of the wave number 4. The observed longitudinal structure of the nighttime EA could not be fully explained by factors such as the empirical electric field and neutral wind models, the geomagnetic declination angle, or the displacement of the geomagnetic equator from the geographic equator. To explain the observed longitudinal structure of the EA, in particular, the wave number 4 feature, we may need to consider other forcing, for example, nonmigrating tide originated from the lower atmosphere.

We report observations of the H+, He+, and O+ polar wind ions in the polar cap (>80° invariant latitude, ILAT) above the collision‐dominated altitudes (>2000 km), from the suprathermal mass spectrometer (SMS) on EXOS D (Akebono). SMS regularly observes low‐energy (a few eV) upward ion flows in the high‐altitude polar cap, poleward of the auroral oval. The flows are typically characteristic of the polar wind, in that they are field‐aligned and cold (Ti < 104 °K), and the parallel (field‐aligned) velocities of the different ion species vary inversely with the respective ion masses. A statistical study of the altitude, invariant latitude, and magnetic local time distributions of the parallel velocities of the respective ion species is described, and preliminary estimates of ion temperatures and densities, uncorrected for perpendicular drifts and spacecraft potential effects, are also presented. For all three ion species, the parallel ion velocity increased with altitude. In the high‐latitude polar cap (>80° ILAT), the average H+ velocity reached 1 km/s near 2000 km, as did the He+ velocity near 3000 km and the O+ velocity near 6000 km. At Akebono apogee (10,000 km), the averaged H+, He+, and O+ velocities were near 12,7, and 4 km/s, respectively. Both the ion velocity and temperature distributions exhibited a day‐to‐night asymmetry, with higher average values on the dayside than on the nightside.

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its ∼1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV-9 keV and 9 eV-16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q-28 keV/q and 7 eV/q-29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the dayside of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.

[1] Recent global-scale observations of the postsunset equatorial O + airglow bands in the F region ionosphere using the IMAGE FUV and TIMED GUVI have revealed a longitudinal wave number four pattern in the magnetic latitude and concentration of the F region peak ion density when measured at a fixed local time. In a new comparison of two data sets with observations made by the OGO 4 satellite, this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross-equator winds during other periods. It is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere. A longitudinal modulation of the dayside equatorial fountain is the most likely driving mechanism. Through comparison with GWSM-02 model, it is shown that the predicted modulation of the dayside thermospheric winds and temperatures at E region altitudes created by non-migrating diurnal tides can explain the modulation in the dayside equatorial fountain. This result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the F region ionosphere. It may also provide a possible further means of testing our understanding of atmospheric tides on a global scale.