On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O + ) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow Manuscript

[1] The distribution of medium-scale irregularities in the total ion density at the equator is investigated. In the scale size range between 10 and 400 km, it is found that, as expected, these irregularities preferentially appear near 2100 local time (LT) in longitude regions that are selected by season according to an alignment between the magnetic meridian and the sunset terminator. However, these irregularities have a maximum occurrence frequency in the postmidnight sector and do not conform to the expected behavior seen for irregularities that appear after sunset. We suggest that the postmidnight peak in the occurrence frequency for these irregularities arose from the weak vertical drifts that prevail in the afternoon and evening during a prolonged solar minimum. It is also suggested that the observed longitude and seasonal dependence in the peak occurrence frequency is influenced by seeding from tropospheric sources, and therefore responds to the seasonal variations in the colocation of the magnetic equator and the Intertropical Convergence Zone. The irregularities appear throughout the nighttime period when the background density is declining rapidly. Thus, despite the postmidnight maximum in occurrence frequency, the maximum absolute perturbation density, most likely to be responsible for radio scintillation, occurs in the premidnight sector.

[1] Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed ±15°away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous data have shown that the peak perturbation in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the results in this paper show that the peak perturbation in parallel flow typically occurs 25-100 km to the east of the peak perpendicular flow. The absence of such a longitudinal offset in previous observations suggests that multiple physical mechanisms may be responsible for creating plasma density enhancements as observed by satellite-borne instrumentation.

[1] Under the waning solar minimum conditions during 2009 and 2010, the Ion Velocity Meter, part of the Coupled Ion Neutral Dynamics Investigation aboard the Communication/Navigation Outage Forecasting System satellite, is used to measure in situ nighttime ion densities and drifts at altitudes between 400 and 550 km during the hours 21:00-03:00 solar local time. A new approach to detecting and classifying well-formed ionospheric plasma depletions and enhancements (bubbles and blobs) with scale sizes between 50 and 500 km is used to develop geophysical statistics for the summer, winter, and equinox seasons during the quiet solar conditions. Some diurnal and seasonal geomagnetic distribution characteristics confirm previous work on equatorial irregularities and scintillations, while other elements reveal new behaviors that will require further investigation before they may be fully understood. Events identified in the study reveal very different and often opposite behaviors of bubbles and blobs during solar minimum. In particular, more bubbles demonstrating deeper density fluctuations and faster perturbation plasma drifts typically occur earlier near the magnetic equator, while blobs of similar magnitude occur more often far away from the geomagnetic equator closer to midnight.

Since the middle of 2008 solar activity has been unusually low, resulting in unusual atmospheric conditions, including significant changes in the pressure and neutral constituents at altitudes near 400 km at low latitudes. These attributes have been measured by the Coupled Ion‐Neutral Dynamics Investigation instruments aboard the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The cross‐track sensor aboard C/NOFS is designed to measure the neutral pressure in an atmosphere with pressures larger than 10−8 Torr, from which the atmospheric scale height can be estimated. In the contracted thermosphere during the current solar minimum (analyzed from June 2008 to August 2009), the instrument data indicate a dominance of neutral helium near the satellite perigee (400 km). This conclusion is found to be consistent with the measured mean drag on the satellite, thus validating the basic functionality of the cross‐track sensor.