A. J. Mannucci

Global dayside ionospheric uplift and enhancement associated with interplanetary electric fields

[1]xa0The interplanetary shock/electric field event of 5–6 November 2001 is analyzed using ACE interplanetary data. The consequential ionospheric effects are studied using GPS receiver data from the CHAMP and SAC-C satellites and altimeter data from the TOPEX/Poseidon satellite. Data from ∼100 ground-based GPS receivers as well as Brazilian Digisonde and Pacific sector magnetometer data are also used. The dawn-to-dusk interplanetary electric field was initially ∼33 mV/m just after the forward shock (IMF BZ = −48 nT) and later reached a peak value of ∼54 mV/m 1 hour and 40 min later (BZ = −78 nT). The electric field was ∼45 mV/m (BZ = −65 nT) 2 hours after the shock. This electric field generated a magnetic storm of intensity DST = −275 nT. The dayside satellite GPS receiver data plus ground-based GPS data indicate that the entire equatorial and midlatitude (up to ±50° magnetic latitude (MLAT)) dayside ionosphere was uplifted, significantly increasing the electron content (and densities) at altitudes greater than 430 km (CHAMP orbital altitude). This uplift peaked ∼2 1/2 hours after the shock passage. The effect of the uplift on the ionospheric total electron content (TEC) lasted for 4 to 5 hours. Our hypothesis is that the interplanetary electric field “promptly penetrated” to the ionosphere, and the dayside plasma was convected (by E × B) to higher altitudes. Plasma upward transport/convergence led to a ∼55–60% increase in equatorial ionospheric TEC to values above ∼430 km (at 1930 LT). This transport/convergence plus photoionization of atmospheric neutrals at lower altitudes caused a 21% TEC increase in equatorial ionospheric TEC at ∼1400 LT (from ground-based measurements). During the intense electric field interval, there was a sharp plasma “shoulder” detected at midlatitudes by the GPS receiver and altimeter satellites. This shoulder moves equatorward from −54° to −37° MLAT during the development of the main phase of the magnetic storm. We presume this to be an ionospheric signature of the plasmapause and its motion. The total TEC increase of this shoulder is ∼80%. Part of this increase may be due to a “superfountain effect.” The dayside ionospheric TEC above ∼430 km decreased to values ∼45% lower than quiet day values 7 to 9 hours after the beginning of the electric field event. The total equatorial ionospheric TEC decrease was ∼16%. This decrease occurred both at midlatitudes and at the equator. We presume that thermospheric winds and neutral composition changes produced by the storm-time Joule heating, disturbance dynamo electric fields, and electric fields at auroral and subauroral latitudes are responsible for these decreases.

The correlation between mid-latitude trough and the plasmapause

[1]xa0We use simultaneous global observations of the mid-latitude trough and the plasmapause to experimentally prove a long-standing conjecture of magnetosphere-ionosphere coupling- namely the mid-latitude trough and plasmapause are on the same field line. Global Ionospheric Maps (GIM), generated using ground based GPS receivers, are used to detect the globally extended mid-latitude trough; while global IMAGE EUV pictures are used to estimate the plasmapause position. Observations during the equinox and solstices and during quiet and disturbed periods are analyzed. In addition, positions of the mid-latitude trough are calculated using a simple empirical model. The two independent observations (mid-latitude trough and plasmapause positions) and an empirical model have been compared on a global scale and found to be in excellent agreement.

Unusual topside ionospheric density response to the November 2003 superstorm

[1]xa0We use observations from a variety of different ground- and space-based instruments, including ionosonde, ground- and space-based Global Positioning System (GPS) receivers, magnetometers, and solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the 20 November 2003 severe storm compared to behavior observed in a number of previous storms. While ground-based GPS receivers observed a large enhancement in dayside TEC, the low-Earth orbiting (∼400 km) CHAMP satellite did not show any sign of dayside TEC enhancement. The real-time vertical density profiles, constructed from ground-based GPS TEC using a tomographic reconstruction technique, clearly revealed that the ionospheric F2-layer peak height had been depressed down to lower altitudes. Ionospheric F-layer peak height (hmF2) from the nearby ionosonde stations over Europe also showed that the dayside F2-layer peak height was below 350 km, which is below the orbiting height of CHAMP. The vertical E × B drift (estimated from ground-based magnetometer equatorial electrojet delta H) showed strong dayside downward drifts, which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high-latitude regions. This storm demonstrates that data from LEO satellites varies widely among different superstorms.

Dayside ionospheric (GPS) response to corotating solar wind streams

The dayside ionospheric modifications associated with the three phases of corotating stream-generated magnetic storms (initial, main and recovery) are investigated. The high density heliospheric current sheet plasmasheet (HCSPS) pressure pulse impingements onto the magnetosphere, the collision of high magnetic field intensity corotating interaction regions (CIRs) onto the magnetosphere, and high speed stream Alfvenic interval ionospheric effects are all investigated using both GPS ground and satellite receiver data. The above results are compared with results associated with magnetic storms caused by interplanetary coronal mass ejections (ICMEs). The main effect found is that southward GSM Bz magnetic fields within CIRS cause an uplift of the dayside ionosphere with the consequence of enhanced ionospheric total electron content (TEC). This limited dayside effect is believed to be due to the variable magnetic field z-components within CIRs. Global dayside and nightside auroral zone ionospheric TEC enhancements are noted associated with the high solar wind Alfvenic intervals. Interpretation of our findings will be given, plus directions for future research in this new and emerging area of space weather.

Extreme solar EUV flares and ICMEs and resultant extreme ionospheric effects: Comparison of the Halloween 2003 and the Bastille Day events

[1]xa0Extreme solar flares can cause extreme ionospheric effects. The 28 October 2003 flare caused a ∼25 total electron content units (TECU = 1016 el/m2 column density), or a ∼30%, increase in the local noon equatorial ionospheric column density. The rise in the TEC enhancement occurred in ∼5 min. This TEC increase was ∼5 times the TEC increases detected for the 29 October and the 4 November 2003 flares and the 14 July 2000 (Bastille Day) flare. In the 260–340 A EUV wavelength range, the 28 October flare peak count rate was more than twice as large as for the other three flares. Another strong ionospheric effect is the delayed influence of the interplanetary coronal mass ejection (ICME) electric fields on the ionosphere. For the 28 and 29 October flares, the associated ICMEs propagated from the Sun to the Earth at particularly high speeds. The prompt penetration of the interplanetary electric fields (IEFs) caused the dayside near-equatorial ionosphere to be strongly uplifted by E × B convection. Consequential diffusion of the uplifted plasma down the Earths magnetic field lines to higher magnetic latitudes is a major plasma transport process during these IEF (superstorm) events. Such diffusion should lead to inverted midlatitude ionospheres (oxygen ions at higher altitudes than protons). The energy input into the midlatitude ionospheres by this superfountain phenomenon could lead to local dayside midlatitude disturbance dynamos, features which cannot propagate from the nightside auroral zones.

Generating climate benchmark atmospheric soundings using GPS occultation data

Atmospheric soundings derived from Global Positioning System radio occultations (GPSRO) acquired in low-Earth orbit have the potential to be global climate benchmark observations of significant value to the Global Climate Observing System (GCOS). Geophysical observables such as atmospheric pressure and temperature are derived by measuring propagation delay induced by the atmosphere, a measurement whose fundamental unit-the second-is absolutely determined by calibration against atomic clocks. In this paper, we analyze the sources of systematic and random error for GPSRO soundings to determine the steps needed to establish GPSRO as a climate benchmark observation. Benchmarks require specific processing strategies and specific forms of documentation so that confidence in the accuracy and precision of the measurements is assured. Establishing calibration traceability to absolute standards (SI-traceability) is an essential strategy. We discuss a wide range of error sources in a geophysical retrieval, such as orbit determination error, signal delay in the Earths ionosphere, and quality control strategies. Uncalibrated ionospheric delay is identified as the error source deserving the most attention in establishing SI-traceability of the retrievals, to meet stringent climate observation requirements of 0.5 K accuracy and 0.04 K stability. Profile comparisons from the recently launched COSMIC constellation establish strong upper limits on systematic error arising from the individual instruments. These encouraging results suggest that GPSRO should become a permanent resource for the GCOS. These highly precise and accurate instruments can be deployed on future Earth Observation satellites at a low per-sensor cost and minimal interference to existing and planned observational programs.

GPS-based remote sensing of the geospace environment: Horizontal and vertical structure of the ionosphere and plasmasphere

Transmissions of the Global Positioning System (GPS) satellites can be used to measure the total electron content (TEC) between a receiver and several GPS satellites in view. This simple observable is yielding a wealth of new scientific information about ionosphere and plasmasphere dynamics. Data available from thousands of ground-based GPS receivers are used to image the large-scale and mesoscale ionospheric response to geospace forcings at high-precision covering all local times and latitudes. Complementary measurements from space-borne GPS receivers in low-Earth orbit provide information on both vertical and horizontal structure of the ionosphere/plasmasphere system. New flight hardware designs are being developed that permit simultaneous measurement of integrated electron content along new raypath orientations, including zenith, cross-track and nadir antenna orientations (the latter via bistatic reflection of the GPS signal off ocean surfaces). We will discuss a new data assimilation model of ionosphere, the Global Assimilative Ionosphere Model (GAIM), capable of integrating measurements from GPS and other sensors with a physics-based ionospheric model, to provide detailed global nowcasts of ionospheric structure, useful for science and applications. Finally, we discuss efforts underway to combine GPS space-based observations of plasmaspheric TEC, with ground-based magnetometer measurements, and satellite-based images from NASAs IMAGE satellite, to produce new dynamic models of the plasmasphere.

Single frequency processing of atmospheric radio occultations

Tracking of the radio signals broadcast by the Global Positioning System (GPS) satellites as they are occulted from a GPS receiver by the Earths atmosphere can provide high resolution vertical profiles of atmospheric refractivity, temperature and water vapour. Most implementations of this radio occultation technique use two GPS frequencies to correct for ionospheric effects. However, during most soundings, one of the frequencies is degraded by the introduction of the so-called Anti-Spoofing (AS) encryption mode. A retrieval method is discussed in this work for periods when only one of the two frequency signals has good quality. This method uses only the frequency with higher signal-to-noise ratio. We illustrate the quality of the atmospheric profiles obtained from such single frequency retrievals using GPS/MET data from the periods where the AS was turned off and the two frequencies were available. The results enable us to ensure the quality of a climate record of thousands of radio occultations collected by GPS/MET during the period with AS encryption, and the data processing of future missions with similar constraints, like IOX, can be performed.

Ionospheric specification algorithms for precise GPS-based aircraft navigation

The Federal Aviation Administration (FAA) is implementing an aircraft navigation scheme for the United States using the Global Positioning System (GPS) L1 signal (1575.42 MHz). To achieve position accuracies of a few meters, sufficient to allow precision airfield approaches, it will be necessary to broadcast corrections to the direct GPS signal. A significant component of these corrections is the delay in the GPS signal introduced by its propagation through the ionosphere. Ionospheric delay corrections will be derived using a ground network of at least 24 dual-frequency GPS receivers distributed across the continental United States. This network is part of the FAAs wide area augmentation system (WAAS) and will provide real-time total electron content (TEC) measurements. We present a technique for converting these TECs into gridded vertical delay corrections at the GPS L1 frequency, which will be broadcast to users every 5 min via geosynchronous satellite. Users will convert these delays to slant corrections for their own particular lines of sight to GPS satellites. To preserve user safety, estimates of the error in the user delay corrections will also be broadcast. However, the error algorithm must not resort to excessive safety margins as this reduces the expected accuracy, and thus utility, of the navigation system. Here we describe an error algorithm and its dependence on various factors, such as user location with respect to the WAAS ground network and ionospheric conditions.

Multiinstrument observations of a geomagnetic storm and its effects on the Arctic ionosphere: A case study of the 19 February 2014 storm

We present a multiinstrumented approach for the analysis of the Arctic ionosphere during the 19 February 2014 highly complex, multiphase geomagnetic storm, which had the largest impact on the disturbance storm-time index that year. The geomagnetic storm was the result of two powerful Earth-directed coronal mass ejections (CMEs). It produced a strong long lasting negative storm phase over Greenland with a dominant energy input in the polar cap. We employed global navigation satellite system (GNSS) networks, geomagnetic observatories, and a specific ionosonde station in Greenland. We complemented the approach with spaceborne measurements in order to map the state and variability of the Arctic ionosphere. In situ observations from the Canadian CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) satellites ion mass spectrometer were used to derive ion flow data from the polar cap topside ionosphere during the event. Our research specifically found that (1) thermospheric O/N2 measurements demonstrated significantly lower values over the Greenland sector than prior to the storm time. (2) An increased ion flow in the topside ionosphere was observed during the negative storm phase. (3) Negative storm phase was a direct consequence of energy input into the polar cap. (4) Polar patch formation was significantly decreased during the negative storm phase. This paper addresses the physical processes that can be responsible for this ionospheric storm development in the northern high latitudes. We conclude that ionospheric heating due to the CMEs energy input caused changes in the polar atmosphere resulting in Ne upwelling, which was the major factor in high-latitude ionosphere dynamics for this storm.