Showing papers on "Longitude published in 2013"

Satellite images suggest a new Sargassum source region in 2011

Abstract: In the summer of 2011, a major ‘Sargassum event’ brought large amounts of seaweed onto the beaches of the islands of the eastern Caribbean with significant effects on local tourism. We present satellite observations showing that the event had its origin north of the mouth of the Amazon in an area not previously associated with Sargassum growth. A significant concentration of Sargassum was detected in April, when it was centred at about 7° N latitude and 45° W longitude. By July it had spread to the coast of Africa in the east and to the Lesser Antilles and the Caribbean in the west. We have previously used images from MERIS (Medium Resolution Imaging Spectrometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) to show the value of satellite observations in tracking patterns of Sargassum. For the years 2003–2010, we were able to determine the seasonal distribution over the range of 20°–40° N latitude and 100°–40° W longitude covering the ‘Sargasso Sea’ region of the North Atlantic and the Gulf o...

Observations of Solar Energetic Particles from ^3He-rich Events over a Wide Range of Heliographic Longitude

Abstract: A prevailing model for the origin of ^3He-rich solar energetic particle (SEP) events attributes particle acceleration to processes associated with the reconnection between closed magnetic field lines in an active region and neighboring open field lines. The open field from the small reconnection volume then provides a path along which accelerated particles escape into a relatively narrow range of angles in the heliosphere. The narrow width (standard deviation 60°. We present the observations of the ^3He-rich event of 2010 February 7, which was detected at all three spacecraft when they spanned 136° in heliographic longitude. Measured fluences of ^3He in this event were found to have a strong dependence on longitude which is well fit by a Gaussian with standard deviation ~48° centered at the longitude that is connected to the source region by a nominal Parker spiral magnetic field. We discuss several mechanisms for distributing flare-accelerated particles over a wide range of heliographic longitudes including interplanetary diffusion perpendicular to the magnetic field, spreading of a compact cluster of open field lines between the active region and the source surface where the field becomes radial and opens out into the heliosphere, and distortion of the interplanetary field by a preceding coronal mass ejection. Statistical studies of additional ^3He-rich events detected at multiple spacecraft will be needed to establish the relative importance of the various mechanisms.

Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude

Abstract: Bipolar active regions in both hemispheres tend to be tilted with respect to the East–West Equator of the Sun in accordance with Joy’s law, which describes the average tilt angle as a function of latitude. Mt. Wilson Observatory data from 1917 – 1985 are used to analyze the active-region tilt angle as a function of solar cycle, hemisphere, and longitude, in addition to the more common dependence on latitude. Our main results are as follows: i) We recommend a revision of Joy’s law towards a weaker dependence on latitude (slope of 0.13 – 0.26) and without forcing the tilt to zero at the Equator. ii) We determine that the hemispheric mean tilt value of active regions varies with each solar cycle, although the noise from a stochastic process dominates and does not allow for a determination of the slope of Joy’s law on an 11-year time scale. iii) The hemispheric difference in mean tilt angles, 1.1∘±0.27, over Cycles 16 to 21 was significant to a three-σ level, with average tilt angles in the Northern and Southern hemispheres of 4.7∘±0.26 and 3.6∘±0.27, respectively. iv) Area-weighted mean tilt angles normalized by latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig et al. (Astron. Astrophys. 518, A7, 2010). The Northern Hemispheric mean tilt angles do not show a dependence on cycle strength. v) Mean tilt angles do not show a dependence on longitude for any hemisphere or cycle. In addition, the standard deviation of the mean tilt is 29 – 31∘ for all cycles and hemispheres, indicating that the scatter is due to the same consistent process even if the mean tilt angles vary.

Non-migrating tides in the ionosphere-thermosphere: In situ versus tropospheric sources

Abstract: [1] In this paper we demonstrate how magnetic control of ion-neutral interactions in the ionosphere-thermosphere (IT) system effectively produces source terms for non-migrating solar tides in the neutral momentum equations for the thermosphere. The National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) is utilized to quantify these tides, and to assess their importance relative to those that propagate upward from lower atmospheric regions. The primary diurnal tides excited in situ by the above mechanism include DE1, D0 and DW2, with zonal wind amplitudes on the order of 20 m s−1 (5–10 m s−1) at ∼500 km (∼350 km) under solar maximum (minimum) conditions. Smaller amplitude semidiurnal non-migrating tides, mainly SE1, S0, SW1, and SW3, are also generated under solar maximum conditions. The aggregate effect of these tidal components is to produce extrema ranging from −110 to +140 m s−1 in a typical illustration of latitude versus longitude at a constant local time. The associated wind circulations include vertical wind perturbations that drive temperature perturbations through adiabatic heating and cooling effects. At high latitudes, hydromagnetic coupling effects generate non-migrating tidal components including DE1, D0, DW2, SE1, S0, and SW1, which show interhemispheric differences in both amplitude and latitudinal structure due to interhemispheric differences in the offset between the geographic and geomagnetic poles. Our computational results show that the in situ generated non-migrating tidal components dominate some parts of the tidal spectrum at high levels of solar activity and suggest that in situ generated non-migrating tides must be taken into account in order to reconcile differences in data-model comparisons.

Recovering Joys Law as a Function of Solar Cycle, Hemisphere, and Longitude

Abstract: Bipolar active regions in both hemispheres tend to be tilted with respect to the East West equator of the Sun in accordance with Joys law that describes the average tilt angle as a function of latitude. Mt. Wilson observatory data from 1917 to 1985 are used to analyze the active-region tilt angle as a function of solar cycle, hemisphere, and longitude, in addition to the more common dependence on latitude. Our main results are as follows: i) We recommend a revision of Joys law toward a weaker dependence on latitude (slope of 0.13 to 0.26) and without forcing the tilt to zero at the Equator. ii) We determine that the hemispheric mean tilt value of active regions varies with each solar cycle, although the noise from a stochastic process dominates and does not allow for a determination of the slope of Joys law on an 11-year time scale. iii) The hemispheric difference in mean tilt angles, 1.1 degrees + 0.27, over Cycles 16 to 21 was significant to a three-sigma level, with average tilt angles in the northern and southern hemispheres of 4.7 degrees + 0.26 and 3.6 degrees + 0.27 respectively. iv) Area-weighted mean tilt angles normalized by latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig, Solanki, Krivova, et al. (2010, Astron. Astrophys. 518, A7). The northern hemispheric mean tilt angles do not show a dependence on cycle strength. vi) Mean tilt angles do not show a dependence on longitude for any hemisphere or cycle. In addition, the standard deviation of the mean tilt is 29 to 31 degrees for all cycles and hemispheres indicating that the scatter is due to the same consistent process even if the mean tilt angles vary.

East-west differences in F-region electron density at midlatitude: Evidence from the Far East region

Abstract: The global configuration of the geomagnetic field shows that the maximum east-west difference in geomagnetic declination of northern middle latitude lies in the US region (similar to 32 degrees), which produces the significant ionospheric east-west coast difference in terms of total electron content first revealed by Zhang et al. (2011). For verification, it is valuable to investigate this feature over the Far East area, which also shows significant geomagnetic declination east-west gradient but smaller (similar to 15 degrees) than that of the US. The current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density (NmF2), electron density (Ne) of different altitudes in the Far East regions with a longitude separation of up to 40-60 degrees based on ground ionosonde and space-based measurements. Although the east-west difference (R-ew) over the Far East area displays a clear diurnal variation similar to the US feature, that is negative R-ew (West Ne > East Ne) in the noon and positive at evening-night, the observational results reveal more differences including: (1) The noontime negative R-ew is most pronounced in April-June while in the US during February-March. Thus, for the late spring and summer period negative R-ew over the Far East region is more significant than that of the US. (2) The positive R-ew at night is much less evident than in the US, especially without winter enhancement. (3) The magnitude of negative R-ew tends to enhance toward solar maximum while in the US showing anticorrelation with the solar activity. The altitude distribution of pronounced negative difference (300-400 km) moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude. The result in the paper is not simply a comparison corresponding to the US results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude. Citation: Zhao, B., M. Wang, Y. Wang, Z. Ren, X. Yue, J. Zhu, W. Wan, B. Ning, J. Liu, and B. Xiong (2013), East-west differences in F-region electron density at midlatitude: Evidence from the Far East region, J. Geophys. Res. Space Physics, 118, 542-553, doi:10.1029/2012JA018235.

Ordering of injection events within Saturnian SLS longitude and local time

Abstract: [1] Periodicities similar to the Saturn kilometric radio (SKR) emissions have been observed throughout the magnetosphere in both the magnetic field and the plasma An outstanding question is what mechanism links these periodicities between the inner and outer magnetospheres It had been postulated that the interchange instability, where narrow injections return the magnetic flux carried by the bulk plasma outflow, could play a role in determining the periodicities, but early analysis found no ordering of the injection events in the SKR-derived Saturnian longitude system (SLS) In this study, we reexamine this possibility by limiting our data set to the young injection events observed by the Cassini radio and plasma wave science instrument We find that the young injection events observed near midnight local time are strongly ordered by SLS Further, this ordering varies with the Saturnian season Pre-equinox, the northern hemisphere's longitude system controls the event occurrence Post-equinox, the events are ordered by the southern hemisphere-derived longitude system We suggest that this may be an effect in the variations in ionospheric conductivity or due to change in the magnetosphere's orientation relative to the solar wind

Formation and variability of the south Pacific sea surface salinity maximum in recent decades

Abstract: [1] This study investigates causes for the formation and variability of the Sea Surface Salinity maximum (SSS > 36) centered near 18 � S–124 � W in the South Pacific Ocean over the 1990–2011 period at the seasonal time scale and above. We use two monthly gridded products of SSS based on in situ measurements, high-resolution along-track Voluntary Observing Ships thermo-salinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a seasonal cycle of the location of the 36-isohaline barycenter of about 6400 km in longitude in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show a low frequency westward shift of the barycenter of 1400 km from the mid 1990s to the early 2010s that could not be linked to the El Nino Southern Oscillation phenomena. In the model, the processes maintaining the 22 year equilibrium of the high salinity in the mixed layer are the surface forcing (�þ 0.73 pss/yr), the horizontal salinity advection (�� 0.37 pss/yr), and processes occurring at the mixed layer base (�� 0.35 pss/yr).

Formation and variability of the South Pacific Sea Surface Salinity maximum in recent decades

Abstract: This study investigates causes for the formation and variability of the Sea Surface Salinity maximum (SSS > 36) centered near 18°S-124°W in the South Pacific Ocean over the 1990-2011 period at the seasonal time scale and above We use two monthly gridded products of SSS based on in situ measurements, high-resolution along-track Voluntary Observing Ships thermo-salinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation All products reveal a seasonal cycle of the location of the 36-isohaline barycenter of about ±400 km in longitude in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity They also show a low frequency westward shift of the barycenter of 1400 km from the mid 1990s to the early 2010s that could not be linked to the El Nino Southern Oscillation phenomena In the model, the processes maintaining the 22 year equilibrium of the high salinity in the mixed layer are the surface forcing (˜+073 pss/yr), the horizontal salinity advection (˜-037 pss/yr), and processes occurring at the mixed layer base (˜-035 pss/yr)

The longitudinal variation of the daily mean thermospheric mass density

Abstract: [1] This study uses the GRACE (Gravity Recovery And Climate Experiment) and CHAMP (CHAllenging Minisatellite Payload) accelerometer measurements from 2003 to 2008. These measurements gave thermospheric mass densities at ~480 km (GRACE) and ~380 km (CHAMP), respectively. We found that there are strong longitude variations in the daily mean thermospheric mass density. These variations are global and have the similar characteristics at the two heights under geomagnetically quiet conditions (Ap < 10). The largest relative longitudinal changes of the daily mean thermospheric mass density occur at high latitudes from October to February in the Northern Hemisphere and from March to September in the Southern Hemisphere. The positive density peaks locate always near the magnetic poles. The high density regions extend toward lower latitudes and even into the opposite hemisphere. This extension appears to be tilted westward, but mostly is confined to the longitudes where the magnetic poles are located. Thus, the relative longitudinal changes of the daily mean thermospheric mass density have strong seasonal variations and show an annual oscillation at high and middle latitudes but a semiannual oscillation around the equator. Our results suggest that heating of the magnetospheric origin in the auroral region is most likely the cause of these observed longitudinal structures. Our results also show that the relative longitude variation of the daily mean thermospheric mass density is hemispherically asymmetric and more pronounced in the Southern Hemisphere.

The ionospheric Sq current system obtained by spherical harmonic analysis

Abstract: [1] An earlier comprehensive analysis of geomagnetic tides by Winch is revisited to display changes in the current systems with season and longitude. The data used come from the quiet Sun years 1964–1965. We choose to present some total equivalent current systems, being the sum of the external and internal parts derived in the spherical harmonic analysis. The latitudes and local times of the current system foci are generally in agreement with other workers. The amplitudes of the current system vortices follow an annual variation with maximum in summer. The longitude variations of the vortex amplitudes vary as the inverse of the magnetic field strength at both equinoxes but have different variations at the solstices. Other longitude maxima which have been reported in the equatorial electrojet intensity were not found. We examine in detail the “invasions” of the summer current systems across the equator, identifying these as signatures of field-aligned currents (FACs). The tilting of current contours with respect to the equator is interpreted as being due to midday FACs. As others have found, the identification of afternoon FACs is more difficult. The seasonal swap-over of FAC directions occurs not in September but in October–November.

Ionospheric symmetry caused by geomagnetic declination over North America

Abstract: [1] We describe variations in total electron content (TEC) in the North American sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination. Patterns were uncovered by applying an empirical orthogonal function (EOF) decomposition procedure to a 12 year ground-based American longitude sector GPS TEC data set. The first EOF mode describes overall average TEC, while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second EOF mode (or the second most significant component). We find a high degree of correlation between spatial variations in the second EOF mode and vertical drifts driven by thermospheric zonal winds, along with well-organized temporal variation. Results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time, season, and solar cycle. This study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range.

Longitude dependences of Saturn's ultraviolet aurora

Abstract: [1] Based on periodicities in the kilometric radio emissions, the Saturn Longitude System 4 (SLS4) was used to organize the far ultraviolet (120–150 nm) aurora observed by the Ultraviolet Imaging Spectrograph on the Cassini spacecraft. Individual Ultraviolet Imaging Spectrograph pixels were projected onto the ionosphere of Saturn, transformed into the SLS4 north and SLS4 south longitude systems, accumulated over all over auroral observations from 2007 to early 2009, and binned into 1°×1° bins of colatitude. The intensity of the northern aurora showed little variation in its SLS4 north system, but the intensity of the southern aurora exhibited an enhancement of over ~10 kR between ~140–280° SLS4 south longitude. This enhancement may represent the auroral signature of a southern ionospheric vortex proposed in MHD models of Saturn's magnetosphere to explain its periodicities. The loci of the northern intensity peaks and the 3 kR boundaries varied little over 360° of longitude, while the equatorward boundary of the southern aurora varied by ~5° in SLS4 south longitude, reaching its most equatorward location of ~23° colatitude between 100° and 180° longitude. The polygonal centroids of the aurora in both north and south were consistent with offsets of no more than ~1° in both hemispheres.

Mean structure of the tropical tropopause and its variability over the Indian longitude sector

Abstract: The mean spatiotemporal variations in tropopause parameters over the tropics (±35°, in latitude) in the Indian monsoon region are examined using the upper air data for an extended period obtained from radiosonde and Radio Occultation measurements. In general, the altitude of cold point tropopause (CPT) is a minimum near the equator and increases with latitude on either side. While CPT over the entire southern tropical latitudes and northern equatorial region is cooler (higher) during boreal winter and warmer (lower) during boreal summer, the annual pattern of CPT-temperature reverses in the northern hemispheric off-equatorial region. The temperature of lapse rate tropopause (LRT) is always negatively correlated with its altitude. While the annual variation of LRT-temperature in tropics is always positively correlated with CPT-temperature, the annual variation of LRT-altitude differs mainly in the off-equatorial regions. While the altitude of the convective tropopause is positively correlated with CPT-altitude over the latitude region 20°S–5°N, they are negatively correlated at the north of 10°N. In general, the tropical tropopause layer (TTL) is very thin (~3 km) near the equator and its thickness increases with latitude on either side of the equator to reach a peak value (of ~6 km) around ±30°. A pronounced decrease in TTL-thickness observed over the northern off-equatorial region during the ASM period can be attributed to the manifestation of very deep convection over the land near the Head Bay-of-Bengal region. The TTL-lapse-rate (γTTL) is large in the equatorial region and decreases with increase in latitude. While γTTL in the northern hemispheric off-equatorial region is low during winter, it increases and becomes comparable to that over equatorial region during the ASM period. The annual variations in CPT parameters as well as the TTL- thickness are significantly modulated by quasi-biennial oscillation and the El Nino Southern Oscillation.

Longitudinal variation in Global Navigation Satellite Systems TEC and topside ion density over South American sector associated with the four-peaked wave structures

Abstract: [1] Recent observations of the low-latitude ionospheric electron density revealed a four-peaked longitudinal structure in the equatorial ionization anomaly when plotted at a constant-local-time frame. It was proposed that neutral wind-driven E region dynamo electric fields due to nonmigrating tidal modes are responsible for this pattern. We examine the four-peaked structure in the observed topside ion density and its manifestation as longitudinal structures in total electron content (TEC) over South America. The strong longitudinal variation in TEC characterized by larger value over Brazilian eastern longitude sector as compared to that over the Peruvian western longitude is modeled using the Sheffield University plasmasphere-ionosphere model (SUPIM) aiming to identify the control factors responsible for the longitude variation. We found that the SUPIM runs using as input the existing standard models of vertical drift, and thermospheric winds do not explain the TEC longitudinal structure. Realistic values of these control parameters were generated based on the strong vertical drift longitudinal variation as determined from magnetometer and Digisonde data and appropriately adjusted winds (horizontal wind model). These realistic vertical drifts together with the modified thermospheric wind, when used as input to the SUPIM, are found to satisfactorily explain the longitudinal differences in the TEC and topside ion density (Ni) over South America. The study shows that the TEC in the whole latitude distribution is larger over the east coast than over the west coast of South America and that the vertical drift and thermospheirc winds control the longitudinal four wave structure in the TEC and Ni.

Performance of Photovoltaic Module for Different Sites in Iraq

Abstract: This paper presents the energy output of photovoltaic (PV) module for three sites in Iraq, these three sites are Mosul (latitude 43°N and longitude 36°E) in the northern Iraq, Baghdad (latitude 33°N and longitude 45°E) in the central Iraq, and Al-Hammar lagoon (latitude 30°N and longitude 46°E) in southern Iraq. The paper analyses the solar radiation data and ambient temperature to compare the PV energy output at these sites. In addition, the environmental aspects are investigated. The analysis showed that the Al-Hammar lagoon is the best location for PV energy production with respect to other locations. It is found that the annual energy production, and reduction of annual greenhouse gases for a module with 215 W capacity are 534 kWh and 0.8 kg of SO2, 0.27 kg of NOx, 324 kg of CO2, respectively.

A Comparison of Two Solar Radiation Models Using Artificial Neural Networks and Remote Sensing in Turkey

Abstract: This study introduces artificial neural networks for the estimation of solar radiation using model 1 (latitude, longitude, altitude, month, and meteorological land surface temperature) and model 2 (latitude, longitude, altitude, month, and satellite land surface temperature) data in Turkey. Price method was used for the estimation of land surface temperature values. Scale conjugate gradiant learning algorithms and logistic sigmoid transfer function were used in the network. R 2 with model 1 and model 2 values have been found to be 96.93 and 97.24% (training stations), 80.41 and 82.37% (testing stations), respectively. These results are sufficient to predict the solar radiation.

Migration and Extension of Solar Active Longitudinal Zones

Abstract: Solar active longitudes show a characteristic migration pattern in the Carrington coordinate system when they can be identified at all. By following this migration, the longitudinal activity distribution around the center of the band can be determined. The halfwidth of the distribution is found to be varying in Cycles 21 - 23, and in some time intervals it was as narrow as 20 - 30 degrees. It was more extended around maximum but it was also narrow when the activity jumped to the opposite longitude. Flux emergence exhibited a quasi-periodic variation within the active zone with a period of about 1.3 years. The path of the active longitude migration does not support the view that it might be associated with the 11-year solar cycle. These results were obtained for a limited time interval of a few solar cycles and, bearing in mind uncertainties of the migration path definition, are only indicative. For the major fraction of dataset no systematic active longitudes were found. Sporadic migration of active longitudes was identified only for Cycles 21 - 22 in the northern hemisphere and Cycle 23 in the southern hemisphere.

Terrain analysis for active tectonic zone characterization: a new application for MODIS night LST (MYD11C3) data set

Abstract: A new context for active tectonic zone recognition is proposed on the basis of the exporting energy of the terrain features at continental scale. Toward this end, elevation, latitude, and longitude decorrelation stretch of multi-temporal moderate resolution imaging spectroradiometer (MODIS) monthly average land surface temperature (LST) imagery (MYD11C3) is applied in a study area extending from Red Sea to Indian Ocean and from Persian Gulf to Black Sea and Caspian Sea. Multiple linear regression analysis of principal components images (principal components analysis (PCAs)) quantified the variance explained by elevation, latitude, and longitude. Selective variance reduction reconstructed the multi-temporal LST imagery from the residual images and selected PCAs by taking into account the portion of variance that is not related to elevation, latitude, and longitude. The reconstructed imagery presents the magnitude the standardized LST value per pixel deviates from the elevation, latitude, and longitude pred...

Quickly Calculate the Distance between Two Points and Measurement Error Based on Latitude and Longitude

Abstract: Directly calculating the distance( arc length) between two points and measurement error by using latitude and longitude,can reduce the link that geodetic coordinates transform into plane coordinates. By deducing the formula of longitude at the arc length of each latitude degree,combining with Excel spreadsheet,can achieve the purpose of rapid operation obtaining the distance( arc length)between two points and the measurement error. This make the calculation simple and convenient,and also improve the calculation method.

Method for locating administrative division based on longitude and latitude

Abstract: The invention relates to a method for locating an administrative division based on a longitude and a latitude. The administrative division where the longitude and the latitude are located is fast located through acquired surveying and mapping data, the method for locating the administrative division based on the longitude and the latitude comprises the steps of locating first administrative divisions where the longitude and the latitude are located, scanning rectangular boundaries corresponding to the first administrative divisions one by one, judging the rectangular boundaries corresponding to the first administrative divisions where the longitude and the latitude are located, and therefore picking out the candidate first administrative divisions; scanning a plurality of polygons contained by any selected candidate first administrative division one by one, judging whether the longitude and the latitude are located in any polygon of the selected first administrative division or not, judging that the selected candidate first administrative division is the first administrative division where the longitude and the latitude are located if the longitude and the latitude are judged to be in any polygon of the selected first administrative division, and returning to continue to scan the rest of the candidate first administrative divisions if the longitude and the latitude are judged not to be in any polygon of the selected first administrative division.

Observations of Ionospheric Flux Ropes above South Pole

Abstract: Numerical techniques have been used to investigate two different models of the current flow in ionospheric flux ropes, giving attention to the problem of mapping the electric field from the ionosphere down to balloon altitudes and to the isolated event that occurred at about 1625 UT on January 3, 1986. Also examined are Greenland magnetometer chain and Iqaluit magnetometer data, which imply that the isolated event was localized in longitude as well as 'global', in the sense that it occurred at conjugate points. IMP 8 solar wind plasma and IMF data indicate that the even occurred just as a strong southward turning of the IMF passed the earth.