Showing papers on "TEC published in 2005"

Tec family kinases in t lymphocyte development and function

Abstract: The Tec family tyrosine kinases are now recognized as important mediators of antigen receptor signaling in lymphocytes. Three members of this family, Itk, Rlk, and Tec, are expressed in T cells and activated in response to T cell receptor (TCR) engagement. Although initial studies demonstrated a role for these proteins in TCR-mediated activation of phospholipase C-gamma, recent data indicate that Tec family kinases also regulate actin cytoskeletal reorganization and cellular adhesion following TCR stimulation. In addition, Tec family kinases are activated downstream of G protein-coupled chemokine receptors, where they play parallel roles in the regulation of Rho GTPases, cell polarization, adhesion, and migration. In all these systems, however, Tec family kinases are not essential signaling components, but instead function to modulate or amplify signaling pathways. Although they quantitatively reduce proximal signaling, mutations that eliminate Tec family kinases in T cells nonetheless qualitatively alter T cell development and differentiation.

Multiradar observations of the polar tongue of ionization

Abstract: [1] We present a global view of large-scale ionospheric disturbances during the main phase of a major geomagnetic storm. We find that the low-latitude, auroral, and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system. For the large geomagnetic storm on 20 November 2003, we examine data from the high-latitude incoherent scatter radars at Millstone Hill, Sondrestrom, and EISCAT Tromso, with SuperDARN HF radar observations of the high-latitude convection pattern and DMSP observations of in situ plasma parameters in the topside ionosphere. We combine these with north polar maps of stormtime plumes of enhanced total electron content (TEC) derived from a network of GPS receivers. The polar tongue of ionization (TOI) is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern. The dayside source of the TOI is the plume of storm enhanced density (SED) transported from low latitudes in the postnoon sector by the subauroral disturbance electric field. Convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral F region is significantly enhanced by the SED material. The three incoherent scatter radars provided full altitude profiles of plasma density, temperatures, and vertical velocity as the TOI plume crossed their different positions, under the cusp, in the center of the polar cap, and at the midnight oval/polar cap boundary. Greatly elevated F peak density (>1.5E12 m 3 ) and low electron and ion temperatures (2500 K at the F peak altitude) characterize the SED/TOI plasma observed at all points along its high-latitude trajectory. For this event, SED/TOI F region TEC (150–1000 km) was 50 TECu both in the cusp and in the center of the polar cap. Large, upward directed fluxes of O+ (>1.E14 m 2 s 1 ) were observed in the topside ionosphere

The October 28, 2003 extreme EUV solar flare and resultant extreme ionospheric effects: Comparison to other Halloween events and the Bastille Day event

Abstract: [1] Some of the most intense solar flares measured in 0.1 to 0.8 nm x-rays in recent history occurred near the end of 2003. The Nov 4 event is the largest in the NOAA records (X28) and the Oct 28 flare was the fourth most intense (X17). The Oct 29 flare was class X7. These flares are compared and contrasted to the July 14, 2000 Bastille Day (X10) event using the SOHO SEM 26.0 to 34.0 nm EUV and TIMED SEE 0.1–194 nm data. High time resolution, ∼30s ground-base GPS data and the GUVI FUV dayglow data are used to examine the flare-ionosphere relationship. In the 26.0 to 34.0 nm wavelength range, the Oct 28 flare is found to have a peak intensity greater than twice that of the Nov 4 flare, indicating strong spectral variability from flare-to-flare. Solar absorption of the EUV portion of the Nov 4 limb event is a possible cause. The dayside ionosphere responds dramatically (∼2.5 min 1/e rise time) to the x-ray and EUV input by an abrupt increase in total electron content (TEC). The Oct 28 TEC ionospheric peak enhancement at the subsolar point is ∼25 TECU (25 × 1012 electrons/cm2) or 30% above background. In comparison, the Nov 4, Oct 29 and the Bastille Day events have ∼5–7 TECU peak enhancements above background. The Oct 28 TEC enhancement lasts ∼3 hrs, far longer than the flare duration. This latter ionospheric feature is consistent with increased electron production in the middle altitude ionosphere, where recombination rates are low. It is the EUV portion of the flare spectrum that is responsible for photoionization of this region. Further modeling will be necessary to fully understand the detailed physics and chemistry of flare-ionosphere coupling.

Theoretical study of the low- and midlatitude ionospheric electron density enhancement during the October 2003 superstorm: Relative importance of the neutral wind and the electric field

Abstract: [1] During magnetic storms the ionospheric total electron content (TEC) at low- and midlatitudes often shows great enhancements, which may be associated with mechanisms producing midlatitude storm-enhanced density (SED). The TEC enhancements may result from different ionospheric drivers such as electric fields, neutral winds, and neutral composition effects. To study the importance of the ionospheric drivers in producing the TEC enhancement, we perform numerical simulations for the 29–30 October 2003 superstorm period in the American longitude sector (∼ −70°W) using the Sheffield University Plasmasphere Ionosphere Model (SUPIM) with values for the neutral wind, temperature, and composition provided by the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere General Circulation Model (TIEGCM). Various numerical experiments were run to identify the relative importance of the storm-time ionospheric drivers. For carrying out the storm-time SUPIM simulation, the storm-time upward/poleward E × B drifts are derived from ROCSAT-1 satellite measurements at low and equatorial latitudes and input to SUPIM, while the storm-time neutral wind and composition disturbances are obtained from TIEGCM run. The simulation results presented in this paper, mainly during the evening period, show that the enhanced upward E × B drifts due to storm-time eastward penetration electric field can expand the low-latitude equatorial ionization anomaly (EIA) to higher latitudes and produce the TEC enhancement. However, by the effect of penetration electric fields alone, the TEC enhancement is less than by combining the storm-generated equatorward neutral winds and the penetration electric fields. Disturbance neutral composition effects decrease the plasma density at higher latitudes and increase it at low and equatorial latitudes. However, the composition effects do not produce a density increase as large as that produced by the neutral-wind and electric-field effects. Our simulations suggest that the storm-generated equatorward neutral winds play an important role in producing the TEC enhancement at low- and midlatitudes, in addition to the eastward penetration electric field.

GPS TEC and scintillation measurements from the polar ionosphere during the October 2003 storm

Abstract: [1] Severe ionospheric storms occurred at the end of October 2003. During the evening of 30 October a narrow stream of high electron concentration plasma crossed the polar cap in the antisunward ionospheric convection. A GPS scintillation receiver in the European high arctic, operating at 1.575 GHz, experienced both phase and amplitude scintillation on several satellite-to-ground links during this period. Close examination of the GPS signals revealed the scintillation to be co-located with strong gradients in Total Electron Content (TEC) at the edge of the plasma stream. The gradient-drift instability is a likely mechanism for the generation of the irregularities causing some of the scintillation at L band frequencies during this storm. The origin of the high TEC is explored and the possible implications of the work for scintillation forecasting are noted. The results indicate that the GPS scintillation over Svalbard can originate from traceable ionospheric plasma structures convecting from the American sector.

TEC-family kinases: regulators of T-helper-cell differentiation

Abstract: The TEC-family protein tyrosine kinases ITK, RLK and TEC have been identified as key components of T-cell-receptor signalling that contribute to the regulation of phospholipase C-gamma, the mobilization of Ca(2+) and the activation of mitogen-activated protein kinases. Recent data also show that TEC kinases contribute to T-cell-receptor-driven actin reorganization and cell polarization, which are required for productive T-cell activation. Functional studies have implicated TEC kinases as important mediators of pathways that control the differentiation of CD4(+) T helper cells. Here, we review studies of signalling pathways that involve TEC kinases and how these pathways might contribute to the regulation of T-helper-cell differentiation and function.

Responses of equatorial anomaly to the October-November 2003 superstorms

Abstract: The responses of Equatorial Ionization Anomaly (EIA) to the superstorms of October- November 2003 were investigated using the total electron content (TEC) measured with global positioning system (GPS) receivers in China, Southeast Asia, Australian (CSAA), and the American regions. Enhanced EIA was seen to be correlated with the southward turning of the interplanetary magnetic field B, In both the CSAA and American regions, EIA was intensified, corresponding to a large increase in the F-layer peak height (hmF2) measured by ionosonde and digisonde at middle and equatorial latitudes. However, the enhanced EIA was shown to be more significant during the daytime in the American region, which was associated with a series of large substorms when B, was stable southward. The prompt penetration electric field and the wind disturbances dynamo electric field are suggested to be responsible for this observation according to current theory, although some features cannot be totally decipherable. Both the ionogram and magnetometer data show the existence of a weak shielding effect whose effect still needs further study. A clear asymmetric ionospheric response was shown in our TEC observations, even though it was only one month after autumnal equinox. The southern EIA crest was totally obliterated on 29 and 30 October in the CSAA region and on 31 October in the American region. Ion temperatures from the Defense Meteorological Satellite Program (DMSP) spacecraft revealed that the unequal energy injection at the polar region might be the reason for this effect. It is concluded that different physical processes have varying degrees of importance on the evolution of EIA in the CSAA and American regions.

Midlatitude TEC enhancements during the October 2003 superstorm

Abstract: [1] We use observations from the array of North American GPS receivers to examine the formation and severity of midlatitude enhancements and steep gradients in total electron content (TEC) during the October 30–31, 2003 superstorm. A large (∼10x) enhancement in dayside TEC was observed over the US mainland during these events as Dst decreased sharply and strong SAPS electric fields eroded the outer reaches of the post-noon plasmasphere boundary layer (PBL) forming poleward-streaming plumes of storm enhanced density. TEC increased to >250 TECu equatorward of the PBL. TEC gradients across the PBL over the central US exceeded 60 TECu per deg latitude. While intense, these features are qualitatively similar to those seen in lesser storms.

Simulation study of penetration electric field effects on the low‐ to mid‐latitude ionosphere

Abstract: [1] The first self-consistent study of the impact of storm-time penetration electric fields on the low- to mid-latitude ionosphere is presented. The inner magnetosphere is described by the Rice Convection Model (RCM) and the ionosphere is described by the Naval Research Laboratory (NRL) code SAMI3. The codes are coupled electrodynamically through the electrostatic potential equation, and the storm is modeled via changes in the polar cap potential. Neutral wind driven electric fields are estimated from the Fejer/Scherliess quiet time model. It is found that temporal changes in the polar cap potential produce electric fields that modify the F region equatorial E × B drift velocities: the velocities increase in the daytime and decrease in the nighttime by up to a factor of two. This causes the total electron content (TEC) in the daytime, mid-latitude ionosphere to increase by up to 35%. In addition, the ‘fountain effect’ is enhanced in the post-sunset period.

Midlatitude TEC enhancements during the October 2003 superstorm : Violent sun-earth connection events of October-November 2003

Abstract: We use observations from the array of North American GPS receivers to examine the formation and severity of midlatitude enhancements and steep gradients in total electron content (TEC) during the October 30-31, 2003 superstorm. A large (∼10x) enhancement in dayside TEC was observed over the US mainland during these events as Dst decreased sharply and strong SAPS electric fields eroded the outer reaches of the post-noon plasmasphere boundary layer (PBL) forming poleward-streaming plumes of storm enhanced density. TEC increased to >250 TECu equatorward of the PBL. TEC gradients across the PBL over the central US exceeded 60 TECu per deg latitude. While intense, these features are qualitatively similar to those seen in lesser storms.

Large-scale variations of the low-latitude ionosphere during the October–November 2003 superstorm: Observational results

Abstract: [1] The GPS-derived total electron content (TEC), ion drift measurements from the ROCSAT-1 spacecraft at around 600 km altitude, and far-ultraviolet airglow measured by the Global Ultraviolet Imager (GUVI) carried on board the NASA TIMED satellite are utilized for studying large disturbances of the low-latitude ionosphere during the October–November 2003 superstorm period. Two chains of GPS receivers, one in the American sector (∼70°W) and the other in the Asian/Australian sector (∼120°E), are used to simultaneously observe the daytime equatorial ionization anomaly (EIA) during the entire storm period. It is found from the GPS-TEC measurements that the EIA expanded to very high latitudes with large increases of TEC right after the storm started. The large expansion of the EIA was associated with strong upward E × B drifts measured from the Ionospheric Plasma and Electrodynamics Instrument (IPEI) on board the ROCSAT-1, providing evidence of a penetration electric field and a strong plasma fountain effect. Suppression of the EIA was observed during the storm recovery, associated with downward E × B drifts that were observed by the ROCSAT-1. Significant negative storm effects in the southern hemisphere were also observed in the GPS-TEC during the first day of the recovery phase. The areas of negative storm effects are in good agreement with reductions in the [O]/[N2] density ratio inferred from the ratio of OI (135.6 nm) to LBH emissions measured from GUVI. An enhancement of the EIA was observed on the day, 1 November, that the storm was about to fully recover.

Performances of thermoelectric cooler integrated with microchannel heat sinks

Abstract: In this study, experimental and theoretical studies on thermoelectric cooler (TEC) performance for cooling a refrigerated object (water in a tank) were performed. Microchannel heat sinks fabricated with etched silicon wafers were employed on the TEC hot side to dissipate heat. The measurements show that the temperature of the refrigerated object decreased with time. A theoretical model based on a lumped system was established to predict the transient behavior of the variation in temperature for the refrigerated object with time. The theoretical predicted temperature variation was in good agreement with the measured data. The relationship among the heat sink thermal resistances, TEC electric current input and minimum refrigerated objected temperature was examined based on the theoretical model. The calculated minimum temperatures were showed for the several cases of heat sink thermal resistance on the TEC hot side and electric current input. The minimum temperature can be obtained by increasing the electrical current input and decreasing the heat sink thermal resistance.

Study of ionospheric response to the 4B flare on 28 October 2003 using International GPS Service network data

Abstract: [1] Using the GPS data from as many as 114 GPS stations of the International GPS Service for Geodynamics (IGS), the morphological features of the ionospheric total electron content (TEC) variations on the sunlit hemisphere during the 4B solar flare on 28 October 2003 is studied. It is found that the strongest sudden increase of TEC (SITEC) happened during the flare, and the magnitudes of SITEC vary at regions with different local solar zenith angle (SZA). In the northern hemisphere, the TEC enhancement is approximately symmetrical to the local noon, and its value is usually greater than 14 TECU (1 TECU = 1016/m2) if the SZA is less than 60°. On the whole, as the SZA increases, the value of TEC enhancement in the northern hemisphere decreases. It is worth mentioning that even in the regions of SZA between 90° and 100°, the SITEC was still seen from the temporal TEC curves. Using a photochemical model, the electron production rate over the sunlit boundary region is calculated and some obvious features of SITEC over this region are analyzed. In the polar region, the effect of this flare on the ionosphere exceeds the effect of the ionospheric scintillations and it seems that the ionosphere in the northern polar region responses more sensitively to this flare. In the end, superimposed on the curves of the rate of TEC change, there are some small disturbances (spikes) synchronously appearing on all curves and thus indicating an existence of similar structures in the EUV band of the flare.

The altitude extension of the mid-latitude trough and its correlation with plasmapause position

Abstract: [1] Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density in an altitude versus geographic latitude grid at a specified longitudinal sector. The method, which involves monitoring the total electron content (TEC) of the ionosphere using signals transmitted from the global positioning system (GPS), has the ability to reveal the detailed structure of the ionosphere including the mid-latitude trough. The tomographic reconstruction of ionospheric electron density structures are performed at different specific longitudinal sectors both in the northern and southern hemisphere. At the same time the plasmapause position is estimated from IMAGE EUV images and mapped onto tomographic images. The simultaneous location of the altitude extension of the mid-latitude trough and the plasmapause position are essentially co-located.

Implications of Ionospheric Scintillation for GNSS Users in Northern Europe

Abstract: Extensive ionospheric scintillation and Total Electron Content (TEC) data were collected by the Institute of Engineering Surveying and Space Geodesy (IESSG) in Northern Europe during years of great impact of the solar maximum on GNSS users (2001–2003). The ionospheric TEC is responsible for range errors due to its time delay effect on transionospheric signals. Electron density irregularities in the ionosphere, occurring frequently during these years, are responsible for (phase and amplitude) fluctuations on GNSS signals, known as ionospheric scintillation. Since June 2001 four GPS Ionospheric Scintillation and TEC Monitor receivers (the NovAtel/AJ Systems GSV4004) have been deployed at stations in the UK and Norway, forming a Northern European network, covering geographic latitudes from 53° to 70° N approximately. These receivers compute and record GPS phase and amplitude scintillation parameters, as well as TEC and TEC variations. The project involved setting up the network and developing automated archiving and data analysis strategies, aiming to study the impact of scintillation on DGPS and EGNOS users, and on different GPS receiver technologies. In order to characterise scintillation and TEC variations over Northern Europe, as well as investigate correlation with geomagnetic activity, long-term statistical analyses were also produced. This paper summarises our findings, providing an overview of the potential implications of ionospheric scintillation for the GNSS user in Northern Europe.

Temporal and spatial variability of the bias between TOPEX- and GPS-derived total electron content

Abstract: Total electron content (TEC) predictions made with the GPS-based la plata ionospheric model (LPIM) and the International Reference Ionosphere (IRI95) model were compared to estimates from the dual-frequency altimeter onboard the TOPEX/Poseidon (T/P) satellite. LPIM and IRI95 were evaluated for the location and time of available T/P data, from January 1997 to December 1998. To investigate temporal and spatial variations of the TEC bias between T/P and each model, the region covered by T/P observations was divided into ten latitude bands. For both models and for all latitudes, the bias was mainly positive (i.e. T/P values were larger); the LPIM bias was lower and less variable than the IRI95 bias. To perform a detailed analysis of temporal and spatial variability of the T/P-LPIM TEC bias, the Earth’s surface was divided into spherical triangles with 9°-sides, and a temporally varying regression model was fitted to every triangle. The highest TEC bias was found over the equatorial anomalies, which is attributed to errors in LPIM. A significant TEC bias was found at 40°N latitude, which is attributed to errors in the T/P Sea State Bias (SSB) correction. To separate systematic errors in the T/P TEC from those caused by LPIM, altimeter range biases estimated by other authors were analysed in connection with the TEC bias. This suggested that LPIM underestimates the TEC, particularly during the Southern Hemisphere summer, while T/P C-band SSB calibration is worse during the Southern Hemisphere winter.

Observations in equatorial anomaly region of total electron content enhancements and depletions

Abstract: . A GSV 4004A GPS receiver has been operational near the crest of the equatorial anomaly at Udaipur, India for some time now. The receiver provides the line-of-sight total electron content (TEC), the phase and amplitude scintillation index, σφ and S4, respectively. This paper presents the first results on the nighttime TEC depletions associated with the equatorial spread F in the Indian zone. The TEC depletions are found to be very well correlated with the increased S4 index. A new feature of low-latitude TEC is also reported, concerning the observation of isolated and localized TEC enhancements in the nighttime low-latitude ionosphere. The TEC enhancements are not correlated with the S4 index. The TEC enhancements have also been observed along with the TEC depletions. The TEC enhancements have been interpreted as the manifestation of the plasma density enhancements reported by Le et al. (2003). Keywords. Ionosphere (Equatorial ionosphere; Ionospheric irregularities)

Ionosphere dynamics over the Southern Hemisphere during the 31 March 2001 severe magnetic storm using multi-instrument measurement data

Abstract: The effects of the 31 March 2001 severe mag- netic storm on the Southern Hemisphere ionosphere have been studied using ground-based and satellite measurements. The prime goal of this comprehensive study is to track the ionospheric response from high-to-low latitude to ob- tain a clear understanding of storm-time ionospheric change. The study uses a combination of ionospheric Total Electron Content (TEC) obtained from GPS signal group delay and phase advance measurements, ionosonde data, and data from satellite in-situ measurements, such as the Defense Metro- logical Satellite Program (DMSP), TOPographic EXplorer (TOPEX), and solar wind data from the Advanced Compo- sition Explorer (ACE). A chain of Global Positioning Sys- tem (GPS) stations near the 150 E meridian has been used to give comprehensive latitude coverage extending from the cusp to the equatorial region. A tomographic inversion algo- rithm has been applied to the GPS TEC measurements to ob- tain maps of the latitudinal structure of the ionospheric dur- ing this severe magnetic storm period, enabling both the spa- tial and temporal response of the ionosphere to be studied. Analysis of data from several of the instruments indicates that a strong density enhancement occurred at mid-latitudes at 11:00 UT on 31 March 2001 and was followed by equa- torward propagating large-scale Travelling Ionospheric Dis- turbances (TIDs). The tomographic reconstruction revealed important features in ionospheric structure, such as quasi- wave formations extending finger-like to higher altitudes. The most pronounced ionospheric effects of the storm oc- curred at high- and mid-latitudes, where strong positive dis- turbances occurred during the storm main phase, followed by a long lasting negative storm effect during the recovery phase. Relatively minor storm effects occurred in the equa- torial region.

A performance evaluation of the operational Jet Propulsion Laboratory/University of Southern California Global Assimilation Ionospheric Model (JPL/USC GAIM)

Abstract: [1] The Jet Propulsion Laboratory/University of Southern California Global Assimilation Ionospheric Model (JPL/USC GAIM) uses two data assimilation techniques to optimally combine ionospheric measurements with the physics model: a sparse, traditional Kalman filter to estimate the three-dimensional density state, and a four-dimensional variational approach (4DVAR) to estimate ionospheric drivers such as the equatorial E × B drift or neutral winds. In this paper we study a specific implementation of the JPL/USC GAIM Kalman filter (single ion, low-resolution, and input data from 200 ground GPS sites) and validate its global accuracy over 137 days by comparisons to independent GPS slant total electron content (TEC) observations (“missing site” tests) and independent JASON vertical TEC observations. The assimilation accuracy is robust with a slant TEC spatial prediction RMS error of 4 TECU (Total Electron Content Unit, 1 × 1016 e-/m2) on average and a vertical TEC JASON RMS error of 7 TECU. Removing what appears to be a positive ≈4.4 TECU bias from the JASON observations, we obtain an improved performance of 5.3 TECU over the oceans. Comparisons with a single, thin shell global ionospheric map model and the International Reference Ionosphere and Bent ionospheric models are also provided.

Total electron content variations in the ionosphere before the Colima, Mexico, earthquake of 21 January 2003

Abstract: Anomalous ionospheric variations associated with the process of strong earthquake (M>5) preparation has been fairly well established. To check possible ionospheric variations connected with the recent Colima earthquake, M=7.8, of 21 January 2003, the data of five stationary GPS receivers of the National Institute of Statistics, Geography and Informatics (INEGI) of Mexico network were analyzed. It was found that the vertical total electron content showed anomalies two to three days before the seismic shock, while the daily cross correlation coefficient calculated for the different pairs of GPS receivers presented a drop within an interval of one to five days before the seismic shock. Also, the horizontal spatial (latitude-longitude) distribution of the TEC deviation had its peak of deviation in a point close to the vertical projection on the ionosphere of the impending earthquake epicenter, thus revealing the local character of the observed anomaly. We conclude, that the observed variations in the ionosphere can be regarded as a possible short-term earthquake precursors.

Two components of ionospheric plasma structuring at midlatitudes observed during the large magnetic storm of October 30, 2003

Abstract: [1] We consider VHF amplitude scintillations, GPS phase fluctuations, ionosonde measurements, maps of GPS total electron content (TEC), observations of daytime aurora and TIMED GUVI images during the large magnetic storms of October 29–31, 2003, and find two distinct classes of plasma processes that produce midlatitude ionospheric irregularities. One is associated with auroral plasma processes; the other, with storm enhanced density (SED) gradients, a part of which occur in close proximity to sub-auroral polarization stream (SAPS) electric fields as discussed by J. C. Foster et al. (2002). We analyze in detail the storm event of October 30, 2003. The SAPS-associated plasma structures may occur by an ion temperature gradient convective instability (M. J. Keskinen et al., 2004), but structuring by auroral processes requires elucidation.

Signaling through CD16b in human neutrophils involves the Tec family of tyrosine kinases

Abstract: Tec kinases belong to the second larg- est family of nonreceptor tyrosine kinases. Al- though these kinases are expressed in myeloid cells, little is known about their implication in neu- trophil function. We recently reported the partic- ipation of Tec kinases in the responses of human neutrophils to the bacterial peptide N-formyl-l-me- thionyl-l-leucyl-l-phenylalanine via G-coupled pro- tein receptors. In this study, we extended our in- vestigations of Tec kinases to the signaling of the glycosylphosphatidylinositol-linked receptor CD16b, which is highly and specifically expressed in neu- trophils. The results obtained indicate that Tec is translocated to the plasma membrane, phosphory- lated, and activated upon CD16b cross-linking and that the activation of Tec is inhibited by Src-spe- cific inhibitors as well as by the phosphatidylinosi- tol-3 kinase inhibitor, wortmannin. As no specific inhibitor of Tec exists, the role of Tec kinases was further investigated using a-Cyano-b-hydroxy-b- methyl-N-(2,5-dibromophenyl)propenamide (LFM- A13), a compound known to inhibit Bruton's ty- rosine kinase. We show that this compound also inhibits the kinase activity of Tec and provide evi- dence that the mobilization of intracellular calcium and the tyrosine phosphorylation of phospholipase C 2( PLC2) induced upon CD16b engagement are inhibited by LFM-A13. We also show that Tec kinases are important for CD16b-dependent de- granulation of neutrophils. In summary, we pro- vide direct evidence for the implication of Tec in CD16b signaling and suggest that Tec kinases are involved in the phosphorylation and activation of PLC2 and subsequently, in the mobilization of calcium in human neutrophils. J. Leukoc. Biol. 78: 524-532; 2005.

Southern Hemisphere ionosphere and plasmasphere response to the interplanetary shock event of 29–31 October 2003

Abstract: [1] We analyze the effects on the Southern Hemisphere ionosphere and plasmasphere due to the 29–31 October 2003 geomagnetic storms (the so-called series of Halloween storms). Solar wind data from ACE and ionospheric data from the GPS (Global Position System) ground and LEO (Low Earth Orbit) receivers, the TOPEX/Poseidon altimeter, the IMAGE FUV camera, and the DMSP drift meter are used to understand the ionospheric dynamics as a function of the storm phase. The detailed structure of the ionosphere has been obtained using tomographic reconstruction applied to data from both ground- and space-based GPS receivers. The tomographic approach using LEO observations of signals received from GPS satellites above the LEO's horizon allows us to investigate the topside ionospheric and plasmaspheric density distribution in more detail than can be obtained using ground-based GPS receivers. This is because with ground-based receivers, the higher topside ionosphere and plasmasphere contribute only a small fraction to the total electron content (TEC) and so the measurements are dominated by the ionospheric structure at the F2 peak. In contrast, the Australian LEO satellite, FedSat, which has been used for this study, orbits at 800 km altitude, well above the F2 peak and hence the TEC measured is primarily due to the upper topside ionosphere and plasmasphere. This paper presents the tomographically reconstructed topside ionosphere and plasmasphere electron density distributions using LEO observations. The temporal and regional maps of TEC and the IMAGE FUV data show that the storm that commenced on 29 October dramatically decreased the plasma density in the Southern Hemisphere middle and high latitudes. The region remained depleted of plasma for more than 24 hours until 31 October, when the second severe storm began. TOPEX/Poseidon data shows a daytime localized density enhancement occurred above the middle of the Pacific Ocean. These results show large interhemispheric and longitudinally narrow storm-time structure in the ionosphere and topside ionosphere/plasmasphere.

Neutral composition effects on ionospheric storms at middle and low latitudes

Abstract: [1] The two-dimensional structure of thermospheric neutral composition, specifically, the atomic oxygen to molecular nitrogen column density ratio, [O/N2], is studied during the 17–24 April 2002 geomagnetic storms to understand the cause of ionospheric storms in regions equatorward of the auroral oval on an instantaneous large scale. The [O/N2] ratio is derived from the dayglow emission ratio of O I 1356 A to N2 Lyman-Birge-Hopfield (1600–1800 A) acquired from the Polar ultraviolet imager (UVI) and the total electron content (TEC), which is used to infer ionospheric storms, is derived from the phase delays of dual-band global positioning satellite (GPS) accumulated around the globe. It is found that the regions of decreasing [O/N2] generally coincided with the regions of depleted TEC during and after the development of the storms. This is consistent with previous theoretical and experimental analysis in which composition changes play a major role in the negative ionospheric storm effects. At lower latitudes, long-lived positive storm effects predicted by empirical and general circulation models were not observed. In fact, there was no noticeable change in [O/N2]. The TEC data also showed no noticeable change, except a few “short-lived,” localized positive TEC perturbations. For this particular event, the equatorward expansion of the decreased [O/N2] at the onset of the first storms was estimated to be more than 600 m/s, much faster than the typical thermospheric wind, and reached ∼30°N in 2 hours much equatorward (>25° MLAT) beyond the auroral electrojets. This result suggests that midlatitude (negative) ionospheric storms are caused by direct equatorward penetration of a reduced thermospheric [O/N2], at least during the first few hours of storms.

The ionospheric impact of the October 2003 storm event on Wide Area Augmentation System

Abstract: The United States Federal Aviation Administration’s (FAA) Wide-Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-transport Satellite-based Augmentation System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. To provide delay corrections for single frequency global positioning system (GPS) users, the wide-area differential GPS systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual-frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEC on regional and global scales. The October 2003 solar-terrestrial events are significant not only for their dramatic scale, but also for their unique phasing of solar irradiance and geomagnetic events. During 28 October, the solar X-ray and EUV irradiances were exceptionally high while the geomagnetic activity was relatively normal. Conversely, 29–31 October was geomagnetically active while solar irradiances were relatively low. These events had the most severe impact in recent history on the CONUS region and therefore had a significant effect on the WAAS performance. To help better understand the event and its impact on WAAS, we examine in detail the WAAS reference site (WRS) data consisting of triple redundant dual-frequency GPS receivers at 25 different locations within the US. To provide ground-truth, we take advantage of the three co-located GPS receivers at each WAAS reference site. To generate ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we process the GPS data using the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This software allows us to compute calibrated high resolution observations of TEC. We found ionospheric range delays up to 35 m for the day-time CONUS during quiet conditions and up to 100 m during storm time conditions. For a quiet day, we obtained WAAS planar fit slant residuals less than 2 m (0.4 m root mean square (RMS)) and less than 25 m (3.4 m RMS) for the storm day. We also investigated ionospheric gradients, averaged over distances of a few hundred kilometers. The gradients were no larger than 0.5 m over 100 km for a quiet day. For the storm day, we found gradients at the 4 m level over 100 km. Similar level gradients are typically observed in the low-latitude region for quiet or storm conditions.

Global response of the low-latitude to midlatitude ionosphere due to the Bastille Day flare

Abstract: [1] The first global simulation study and comparison to data of the ionospheric effects associated with the enhanced EUV irradiance of the Bastille Day flare are presented. This is done by incorporating a time-dependent EUV spectrum, based on data and hydrodynamic modeling, into the NRL ionosphere model SAMI3. The simulation results indicate that the total electron content (TEC) increases to over 7 TEC units in the daytime, low-latitude ionosphere. In addition, it is predicted that the maximum density in the F-layer (NmF2) increases by ≲20% and that the height of the maximum electron density (HmF2) decreases by ≲20%. These results are explained by the increased ionization at altitudes <400 km which increases TEC and NmF2 while decreasing HmF2. The results are in reasonably good agreement with data obtained from GPS satellites and the TOPEX satellite.