Broad Plasma Decreases in the Equatorial Ionosphere

• Main Authors: Huang, Cheryl Y., Marcos, Frank A., Roddy, Patrick A., Hairston, Marc R., Coley, W. R., Roth, Christopher, Bruinsma, Sean, Hunton, Donald E.
• Other Authors: AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
• Format: Text
• Language: English
• Published: 2009
• Subjects: Atmospheric Physics; Meteorology; *IONOSPHERE; *PLASMAS(PHYSICS); *EQUATORIAL REGIONS; BUBBLES; LANGMUIR PROBES; PLANAR STRUCTURES; SOUTH ATLANTIC OCEAN; REPRINTS; WEATHER FORECASTING; PLP(PLANAR LANGMUIR PROBE); BPD(BROAD PLASMA DENSITY); C/NOFS(COMMUNICATIONS/NAVIGATION OUTAGE FORECASTING SYTEM); SAA(SOUTH ATLANTIC ANOMALY); CHAMP(CHALLENGING MINISATELLITE PAYLOAD); DMSP(DEFENSE METEOROLOGICAL PROGRAM); EPB(EQUATORIAL PLASMA BUBBLES); PE62601F; WUAFRL2301SDA5; Langmuir; South Atlantic Ocean
• Online Access: http://www.dtic.mil/docs/citations/ADA528206; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA528206

During June 2008 broad plasma density decreases (BPDs) were detected repeatedly by the Planar Langmuir Probe (PLP) on board the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. These density minima, not to be confused with Equatorial Plasma Bubbles (EPBs), occurred within 15 degrees of the equator, consisted of reductions in plasma density up to an order of magnitude and extended across several degrees in azimuth along the orbit. Analysis revealed that the BPDs occurred nearly daily from May through July 2008 on C/NOFS, and that the widest BPDs were observed in the vicinity of the South Atlantic Anomaly (SAA). Similar BPDs simultaneous with the C/NOFS measurements were observed by instruments on the CHAllenging Minisatellite Payload (CHAMP) and Defense Meteorological Program (DMSP) satellites. An examination of plasma densities revealed that these phenomena were a frequent occurrence during (1) the period around June solstices; during (2) solar minimum years); (3) in the vicinity of the SAA. Neutral densities were examined during periods when BPDs were detected, and at times there are simultaneous neutral depletions. One possible explanation is a decrease in temperature of both ions and neutrals in the equatorial region at these times, consistent with downwelling in the ionosphere and thermosphere. Measurements of plasma temperatures on DMSP support this hypothesis. Published in Geophysical Research Letters, v36 nL00C04 p1-5, 2009.