Showing papers on "Longitude published in 2011"

Statistics of total electron content depletions observed over the South American continent for the year 2008

Abstract: [1] This paper presents for the first time regional plots of total electron content (TEC) depletions derived from GPS observations over the South American continent with a coverage of over 45° longitude (i.e., 35°W to 80°W). We introduce a new numerical algorithm that has been developed to automatically detect TEC bite-outs that are produced by the transit of equatorial plasma bubbles. This algorithm was applied to TEC values measured by the Low Latitude Ionospheric Sensor Network (LISN) and by receivers that belong to 3 other networks that exist in South America. The general characteristics of the TEC depletions are provided along with their temporal length, local time distribution and depletion depth. The regional day-to-day and seasonal variability of the TEC depletions are also presented for 2008, a year of low solar activity. The regional day-to-day variability of TEC depletions is highly dynamic, but their seasonal distributions follow the longitudinal characteristics of plasma bubbles presented by other authors. During the equinoxes, TEC depletions are mainly observed on the west coast of South America, and during the December solstice they mostly occur on the east side of the continent. However, in all seasons, we observe days when depletions extend all over the continent. We place these new results in the context of theories of plasma bubble seeding.

A gridded sea surface salinity data set for the tropical Pacific with sample applications (1950-2008)

Abstract: We present a gridded data set of Sea Surface Salinity (SSS) for the tropical Pacific (1201E–701W; 301N–301S), with a grid resolution of 11 longitude, 11 latitude and 1 month, from 1950 to 2008. The product, together with its associated error field, is derived from an objective analysis of about 10 million validated SSS records, with most of the data originating from Voluntary Observing Ships, TAO/TRITON moorings and Argo profilers (during the most recent period). We expect this product to benefit studies in oceanography, meteorology

The Moon’s physical librations and determination of their free modes

Abstract: The Lunar Laser Ranging experiment has been active since 1969 when Apollo astronauts placed the first retroreflector on the Moon. The data accuracy of a few centimeters over recent decades, joined to a new numerically integrated ephemeris, DE421, encourages a new analysis of the lunar physical librations of that ephemeris, and especially the detection of three modes of free physical librations (longitude, latitude, and wobble modes). This analysis was performed by iterating a frequency analysis and linear least-squares fit of the wide spectrum of DE421 lunar physical librations. From this analysis we identified and estimated about 130–140 terms in the angular series of latitude librations and polar coordinates, and 89 terms in the longitude angle. In this determination, we found the non-negligible amplitudes of the three modes of free physical libration. The determined amplitudes reach 1.296′′ in longitude (after correction of two close forcing terms), 0.032′′ in latitude and 8.183′′ × 3.306′′ for the wobble, with the respective periods of 1056.13 days, 8822.88 days (referred to the moving node), and 27257.27 days. The presence of such terms despite damping suggests the existence of some source of stimulation acting in geologically recent times.

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

Abstract: Context. CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Aims. Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. Methods. We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2 ◦ . Results. Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, which is reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of −14. ◦ 6 ± 10 ◦ is obtained from the auto-correlation function of the time-integrated spot flux deficit, which yields a rotation period of 4.48 days. With this period, the temporal evolution of the spot surface coverage in individual 20 ◦ longitude bins has periodicities ranging from 9 to 53 days with an average value of 31 ± 15 days. On the other hand, the longitude integrated spot flux, which is independent of the stellar rotation period, oscillates with a periodicity of 17.7 days, and its false-alarm probability is ∼3%. Conclusions. The rotation period of 4.48 days obtained here is shorter than the 4.54 days derived from the out-of-transit light modulation. Because the transit data sample a region close to the stellar equator while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d.

East-West Coast differences in total electron content over the continental US

Abstract: [1] Total electron content (TEC) measurements made by a network of dense GPS receivers over the continental US are used to investigate ionospheric longitudinal differences. We find that the evening TEC is substantially higher on the US east coast than on the west, and vice versa for the morning TEC; the longitudinal difference displays a clear diurnal variation. Through an analysis of morning-evening variability in the east-west TEC difference, minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental US. We suggest that these new findings of longitudinal differences in ionospheric TEC at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day. This study indicates that longitudinal variations in TEC measurements contain critical information on thermospheric zonal winds. The proposed declination-zonal wind mechanism may also provide a new insight into longitude/UT changes at midlatitudes on a global scale, as well as into some geospace disturbances.

Longitudinal variations in the F region ionosphere and the topside ionosphere‐plasmasphere: Observations and model simulations

Abstract: [1] Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) observations of the total electron content (TEC) above and below 800 km are used to study the local time and seasonal variation of longitude structures in both the F region ionosphere as well as the topside ionosphere and plasmasphere. The COSMIC observations reveal the presence of distinct longitude variations in the topside ionosphere-plasmasphere TEC, and these further exhibit a seasonal and local time dependence. The predominant feature observed at all local times in the topside ionosphere-plasmasphere TEC is a substantial maximum (minimum) during Northern Hemisphere winter (summer) around 300°–360° geographic longitude. Around equinox, at a fixed local time, a wave 4 variation in longitude prevails in the daytime F region TEC as well as the topside ionosphere-plasmasphere TEC. The wave 4 variation in longitude persists into the nighttime in the F region; however, the nighttime topside ionosphere-plasmasphere TEC exhibits two maxima in longitude. The COSMIC observations clearly reveal the presence of substantial longitude variations in the F region and topside ionosphere-plasmasphere, and to elucidate the source of the longitude variations, results are presented based on the coupling between the Global Ionosphere Plasmasphere model and the Thermosphere Ionosphere Electrodynamics General Circulation Model. The model simulations demonstrate that the orientation of the geomagnetic field plays a fundamental role in generating significant longitude variations in the topside ionosphere-plasmasphere but does not considerably influence longitude variations in the F region ionosphere. The model results further confirm that nonmigrating tides are the primary mechanism for generating longitude variations in the F region ionosphere. The coupled model additionally demonstrates that nonmigrating tides are also of considerable importance for the generation of longitude variations in the topside ionosphere-plasmasphere TEC.

Equatorial electrodynamics and neutral background in the Asian sector during the 2009 stratospheric sudden warming

Abstract: Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major stratospheric sudden warming (SSW) in January 2009. Our analysis reveals the following prominent features. First, the TEC response in tropical regions is strongly latitude dependent, with monotonic depletion at the dip equator but a semidiurnal perturbation at low latitudes. Second, the TEC semidiurnal perturbation possesses a significant hemispheric asymmetry in terms of onset date and magnitude. It starts on the same day as the SSW peak in the Northern Hemisphere but 2 days later in the Southern Hemisphere. Its magnitude is twice as strong in the north than in the south. Third, strong counter electrojet occurs in the afternoon, following the strengthening of the eastward EEJ in the morning. Fourth, semidiurnal perturbation in both TEC and EEJ possesses a phase shift, at a rate of about 0.7 h/day. Comparisons with results reported in the Peruvian sector reveal clear longitude dependence in the amplitude and hemispheric asymmetry of the semidiurnal perturbation. Finally, thermospheric density undergoes ?25% decrease at low latitudes in the afternoon local time sector during the SSW, indicating significant cooling effects in the tropical upper thermosphere.

An SLS4 Longitude System Based on a Tracking Filter Analysis of the Rotational Modulation of Saturn Kilometric Radiation

Abstract: Saturn has been known for over thirty years to emit an intense radio emission at kilometer wavelengths called Saturn Kilometric Radiation (SKR) that is modulated by the rotation of the planet. Although the period of this modulation was initially thought to represent the rotation period of the planet, it is now known that the radiation has two distinctly different rotational modulation periods that vary by on the order of one percent on times scales of years. One component originates primarily from the northern auroral region, and the other originates primarily from the southern auroral region. The differences in the modulation periods are believed to be due to latitudinal variations in the slippage of the magnetosphere relative to the interior of planet, apparently controlled by the seasonal variation in the tilt of Saturn’s rotational axis. Since other magnetospheric phenomena display similar complicated rotational modulation effects, there is a need to define north and south longitude systems based on the variable SKR modulation periods in the two hemispheres. Because the SKR signal received by the spacecraft often includes both components it is sometimes difficult to separate the phases of the two components. In this paper we describe a method of determining the two phases based on a tracking filter approach that can separately track the modulation waveforms of the two components. The phases of the two waveforms can then be used to define a new longitude system for the northern and southern components that we call the SLS4 longitude system. This is an extension of the previous SLS2 and SLS3 longitude systems, which only described phase variations of the southern component.

Controls on the Spatial Variability of Modern Meteoric 18O: Empirical Constraints from the Western U.S. and East Asia and Implications for Stable Isotope Studies

Abstract: We analyze a dataset of multiannual modern precipitation and meteoric water records from the western U.S. (n = 206) and east Asia (n = 478) to (1) determine which environmental parameters correlate best with and account for spatial variability of meteoric water isotopic (δ18O and δD) compositions and (2) assess the degree to which this variability is a function of physiography and climatology. Multivariate linear regression analysis including five environmental parameters [latitude, longitude, elevation, mean annual temperature (MAT), mean annual precipitation (MAP)] reveals that latitude and elevation are consistently strongly correlated with meteoric δ18O distributions throughout much of the western U.S. and east Asia, but correlations with site longitude, MAT, and MAP can also be significant, depending on region. Our analysis also indicates that isotope-environment relationships are region-dependent. Isotope-elevation gradients are reduced by a factor of two or more in continental interior rainshadows (for example, Basin and Range) and high elevation continental plateaus (for example, Tibetan Plateau) in comparison to isotope-elevation gradients observed in orographic settings with a single dominant moisture source and relatively simple storm track trajectories (for example, Sierra Nevada and Himalaya). Published global and continental predictive equations for the calculation of modern meteoric water isotopic compositions that do not account for this regional variability are shown to be characterized by significant predictive uncertainties for modern δ18O values (∼ ±3-4‰), particularly in regions of complex moisture source interactions, continental moisture recycling and increased convective storm activity where reduced isotope-elevation gradients are also observed. We present new empirical relationships between environmental parameters and isotopic compositions that inform stable isotope-based reconstructions of climate change, timing and location of groundwater recharge, and paleoaltimetry by providing quantitative constraints on the statistical relationship between precipitation δ18O and individual environmental parameters (for example, latitude, elevation, temperature) and identifying how isotopic relationships are influenced by physiography and climatology. In particular, paleoelevation estimates in regions of low-magnitude isotope-elevation gradients (Basin and Range, Tibet) are shown to be prone to significant uncertainties (in some cases > ±2 km). These relationships improve the interpretation of stable isotope proxy data, particularly in cases where the paleogeographic setting of proxy formation can be constrained.

Global characteristics of occurrence of an additional layer in the ionosphere observed by COSMIC/FORMOSAT-3

Abstract: Global observations of electron density profile (EDP) from the COSMIC/FORMOSAT-3 satellites were used to investigate, for the first time, the additional stratification of the F2 layer over the equatorial ionosphere on a global scale, which is called F3 layer. The F3 layer in EDP was recognized through the altitude differential profile featured by two maxima existing from 220 km to the peak height of the electron density. There were similar to 9,400 cases of F3 layer selected out of similar to 448, 000 occultation events at low and equatorial areas during the period of April 2006-September 2010. Statistical results show that the highest occurrence of F3 layer appears at dip latitude 7 similar to 8 degrees/-7 similar to-8 degrees for Northern/Southern Hemisphere and is more pronounced during summer months at 10:00-14:00 LT. The occurrence also has a clear longitude dependence during boreal summer, with relatively higher occurrence at -80 similar to-100 degrees, -20 similar to 20 degrees, 80 similar to 120 degrees and -160 similar to-170 degrees longitudes, that is possibly associated with the wavenumber-3 diurnal tide (DE3). The results support the principle of the F3 layer proposed by Balan et al. (1998), which in turn validate the accuracy of the retrieval of the COSMIC EDP data. Citation: Zhao, B., W. Wan, X. Yue, L. Liu, Z. Ren, M. He, and J. Liu (2011), Global characteristics of occurrence of an additional layer in the ionosphere observed by COSMIC/FORMOSAT-3, Geophys. Res. Lett., 38, L02101, doi:10.1029/2010GL045744.

Latitudinal distribution of anomalous ion density as a precursor of a large earthquake

Abstract: [1] Data obtained by the U.S. satellite DE‐2 are used to investigate possible precursor features in the ionosphere associated with a large earthquake (latitude �33.13°, longitude 73.07°, M = 7.5), which occurred during a moderate geomagnetic disturbance. Atomic oxygen ion and molecular ion distributions show characteristic latitudinal features similar to the well‐known equatorial ionization anomaly (EIA) feature but centered around the earthquake epicenter. We name this the precursor ionization anomaly (PIA). The density minima of both the atomic oxygen and molecular ions are in two latitude zones, depending on the distance from the epicenter. One of the PIA minima aligns with the geomagnetic latitude crossing the epicenter. Another minimum is found along the geographic latitude of the epicenter. These minima are located in an area spanning about 40° in latitude and about 140° in longitude. It is noted that the molecular ion minimum is more clearly defined even when the atomic ion density minimum is not indicated clearly. The ion density reduction seems to be caused by a superposition of natural/quiet time ionospheric eastward electric field and an electric field associated with the earthquake. Although we studied one single event, our careful examination of results suggests that the location and day of occurrence of the PIA can be predicted for some large earthquakes even during moderate geomagnetic disturbance if the satellite orbit is properly chosen.

The winter anomaly in the middle‐latitude F region during the solar minimum period observed by the Constellation Observing System for Meteorology, Ionosphere, and Climate

Abstract: [1] The winter anomaly (or seasonal anomaly) at middle latitudes is a phenomenon during which the daytime plasma density at the F-peak height (NmF2) is greater in winter than in summer. Radio occultation measurements from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites provide a new data source for study of the winter anomaly on a global scale. In this study we investigate the altitude, local time, latitude, longitude, and hemispheric variations of the electron density in the middle-latitude ionosphere by analyzing the COSMIC data measured in 2007 during a magnetically quiet period (Kp ≤ 3). The seasonal mean behavior of the NmF2 obtained from COSMIC data shows the occurrence of the winter anomaly feature during 0800–1600 LT in the Northern Hemisphere but not in the Southern Hemisphere. The intensity of the winter anomaly is variable with longitude, and a more intense winter anomaly is likely to occur at longitudes closer to the magnetic pole. At northern middle latitudes, a greater electron density in the winter than in the summer occurs in the narrow altitude range near the F-peak height. Except for the winter anomaly feature at northern middle latitudes, the electron density at middle latitudes is greater during the summer than during the winter in both hemispheres.

Seasonal and longitudinal variations of the solar quiet (Sq) current system during solar minimum determined by CHAMP satellite magnetic field observations

Abstract: [1] Vector magnetometer observations from the Challenging Minisatellite Payload (CHAMP) satellite are used to determine the solar quiet (Sq) current system during the recent solar minimum. Observations from 2006 to 2008 are combined, and after removal of a main field model and accounting for field-aligned currents, the longitudinal and seasonal variation of the Sq currents are determined through the method of spherical harmonic analysis. Comparison with Sq currents derived from ground-based magnetometers in the African/European longitude sector reveals similar amplitudes and seasonal variations, indicating that the CHAMP observations can reliably determine the Sq current system. The seasonal variation is consistent with prior observations during solar minimum conditions and in the Northern Hemisphere exhibits a primarily annual variation with peak currents during local summer. The seasonal variation in the Southern Hemisphere is characterized by a semiannual variation with the maxima occurring around the equinoxes. Significant longitudinal variations are also observed, and they display a seasonal variability. During Northern Hemisphere summer, the predominant feature at local noon is a wave number 1 variation in longitude. During the remainder of the year, a wave 3 longitudinal structure is observed at this local time. The longitudinal variations are considered to be due to a combination of the orientation and strength of the geomagnetic field as well as the tidal winds in the lower thermosphere. Variations in tidal winds due to nonmigrating tides may influence the dynamo-generated electric fields and currents, resulting in the observed longitudinal variations of the Sq current function.

Climatology of the inter-hemispheric field-aligned current system in the equatorial ionosphere as observed by CHAMP

Abstract: . From geomagnetic field observations of CHAMP during 2001–2009 we extracted characteristic signatures of inter-hemispheric field-aligned currents (IHFACs) in the equatorial ionosphere. The results are in general agreement with previous observations. Nighttime IHFACs are negligibly small. Solstitial IHFACs flow from the summer to winter (from winter to summer) hemisphere at dawn (around noon). Duskside IHFACs flow southbound irrespective of season. We have also found some new IHFAC properties, which may have been predicted by theories, but are not yet given observational support. IHFACs clearly exhibit a longitude dependence, which is modulated by the South Atlantic Anomaly, the offset between geographic and magnetic equators, and tidal waves. IHFACs show little dependence on the solar cycle. We provide a comprehensive assessment of the IHFAC modulation by non-migrating tides.

Diurnal and seasonal variation of GPS-TEC during a low solar activity period as observed at a low latitude station Agra

Abstract: between the two. Further, GIMs of TEC have been analysed for five different latitudes along the common meridian of 80 0 E longitude. The present study has been carried out for three months of the year 2009 in each season. The role of equatorial ionization anomaly (EIA) crest is clearly visible on TEC data. These results are significant for Agra station which is a new location in the low latitude sector of Indian region.

Sq field characteristics at Phu Thuy, Vietnam, during solar cycle 23: comparisons with Sq field in other longitude sectors

Abstract: . Quiet days variations in the Earth's magnetic field (the Sq current system) are compared and contrasted for the Asian, African and American sectors using a new dataset from Vietnam. This is the first presentation of the variation of the Earth's magnetic field (Sq), during the solar cycle 23, at Phu Thuy, Vietnam (geographic latitudes 21.03° N and longitude: 105.95° E). Phu Thuy observatory is located below the crest of the equatorial fountain in the Asian longitude sector of the Northern Hemisphere. The morphology of the Sq daily variation is presented as a function of solar cycle and seasons. The diurnal variation of Phu Thuy is compared to those obtained in different magnetic observatories over the world to highlight the characteristics of the Phu Thuy observations. In other longitude sectors we find different patterns. At Phu Thuy the solar cycle variation of the amplitude of the daily variation of the X component is correlated to the F.10.7 cm solar radiation (~0.74). This correlation factor is greater than the correlation factor obtained in two observatories located at the same magnetic latitudes in other longitude sectors: at Tamanrasset in the African sector (~0.42, geographic latitude ~22.79) and San Juan in the American sector (~0.03, geographic latitude ~18.38). At Phu Thuy, the Sq field exhibits an equinoctial and a diurnal asymmetry: – The seasonal variation of the monthly mean of X component exhibits the well known semiannual pattern with 2 equinox maxima, but the X component is larger in spring than in autumn. Depending of the phase of the sunspot cycle, the maximum amplitude of the X component varies in spring from 30 nT to 75 nT and in autumn from 20 nT to 60 nT. The maximum amplitude of the X component exhibits roughly the same variation in both solstices, varying from about ~20 nT to 50 nT, depending on the position into the solar cycle. – In all seasons, the mean equinoctial diurnal Y component has a morning maximum Larger than the afternoon minimum i.e. the equivalent current flow over a day is more southward than northward. During winter, the asymmetry is maximum, it erases the afternoon minimum. At the Gnangara observatory, in Asian Southern Hemisphere, the diurnal Y pattern is opposite and the current flow is more northward. It seems that in the Asian sector, the northern and southern Sq current cells both contribute strongly to the equatorial electrojet. The pattern is different in the African and American sectors where the northern Sq current cell contribution to the equatorial electrojet is smaller than the southern one. These observations can explain the unexpected maximum of amplitude of the equatorial electrojet observed in the Asian sector where the internal field is very large. During winter the Y component flow presents an anomaly, it is always southward during the whole day and there is no afternoon northward circulation.

Onset conditions of bubbles and blobs: A case study on 2 March 2009

Abstract: [1] The onset conditions for bubbles and blobs are investigated by analyzing the Communication/Navigation Outage Forecasting System satellite/Coupled Ion-Neutral Dynamics Investigation instrument data on 2 March 2009 A series of bubbles and blobs are detected in the longitude regions 180°–240°E and 240°–295°E, respectively Bubbles are detected at low latitudes before midnight Blobs are detected at 14°–25° magnetic latitude, between 2300 and 0500 LT in the altitude range of 400–480 km The distinguishing feature in the longitude region where bubbles are detected is an enhancement in background plasma density with respect to that in the longitude region where bubbles are absent Blobs are detected in a longitude region where fluctuations in the plasma density exist over a broad latitude range The total ion density (and O+ density) and H+ density perturbations are in-phase at the locations of bubbles and out of phase at the locations of blobs Bubbles are not detected in the longitude region where blobs are detected The different characteristics of bubbles and blobs and their creation under different geophysical conditions indicate that creation of blobs need not be associated with bubbles

Airglow observations and modeling of F region depletion zonal velocities over Christmas Island

Abstract: [1] We report image measurements of plasma depletions in the equatorial F region ionosphere over Christmas Island (2.1°N, 157.4°W; dip latitude 2.8°N) in the central Pacific Ocean. The observations were made during the equinox period, September-October 1995, using a Utah State University CCD imaging system filtered to observe thermospheric O I (630.0 nm) airglow emissions centered at ∼280 km altitude. Well-defined magnetic field-aligned depletions were observed on 18 nights during the campaign, including strong postmidnight fossilized structures, enabling detailed measurements of their morphology and dynamics. The number of depletions was influenced by their initial onset times and their persistence. The separations between adjacent depletions ranged from ∼150 to ∼250 km in good agreement with prior observations from other sites. However, measurements of their eastward zonal drift speeds indicated normal behavior peaking around 90–100 m/s prior to local midnight, with exceptionally high velocities, ∼80 m/s during the postmidnight period that persisted until dawn. These results differ markedly from optical measurements at similar equatorial latitudes but at different longitude sectors, suggesting that the zonal drift velocities can have a significant longitudinal dependence. Model drift velocities calculated using a simple electric field model with winds defined by the horizontal wind model (HWM-07) produced an eastward drift throughout the night, but their postmidnight magnitudes were much smaller than observed. Using a modified HWM-07 wind field, a basic nighttime trend similar to the Christmas Island trend was successfully obtained.

Zonal structure of the mean flow and eddies in the Azores Current system

Abstract: [1] The surface circulation and eddy field from the Azores Current system are studied here by analyzing surface drifters records and altimetry maps collected over more than 16 years. Clear differences in mean flow and eddy characteristics allow for a classification of the Azores Current in three zonal sectors: west of 30°W between the Mid-Atlantic Ridge and the Hyeres-Atlantis seamount system, between 30°W and the longitude of Madeira, and east of Madeira. A detailed and quantitative characterization of each sector is given. The transition between the western and central parts is controlled by the Hyeres-Atlantis ridge. In the transition to the eastern sector there is a change in the dynamics and the flow is forced by the cyclonic recirculation driven by the Mediterranean outflow. There is no clear expression of a continuous surface northern counterflow, but three distinct westward flows are seen: one along the southeastern border of the Azores plateau, another one southwest of Madeira, and a third one along 31°N west of the Hyeres seamount. No clear tilt in the axis of the Azores Current is found in the calculated mean surface flow from surface drifters. Observations from both drifters and altimetry data show that anticyclonic features dominate in the northern region, whereas cyclonic ones dominate in the southern region. Overall, cyclones are more numerous, constituting 60% of large eddies. The eddy features detected in the west tend to be larger than those in the east, both in size and sea level anomaly. There is indication of different mean propagation speeds east and west of 25°W–30°W, with the mean speeds consistently increasing by 25%–45% in the west. Estimates for the rate of formation of strong eddies range from 1.4 to 2.4 year−1 for cyclones, and 1.2 to 1.7 year−1 for anticyclones.

Response of low-latitude ionospheric total electron content to the geomagnetic storm of 24 August 2005

Abstract: [1] Response of low-latitude ionosphere to the geomagnetic storm of 24 August 2005 has been studied using total electron content (TEC) data obtained from the Global Positioning System (GPS) receivers. These studies were carried out using the receivers that were located (1) near the northern crest (∼15°N mag. Lat.) of the equatorial ionization anomaly around 56°E, 74°E, and 102°E longitude and (2) from the northern crest of the ionization anomaly down to the magnetic equator in the longitude belt 75°E ± 3°E. These studies have been substantiated with the ground-based magnetometer data at Tirunelveli and Alibag, an equatorial and off equatorial station, respectively. The ground-based ionosonde data at New Delhi, a low-latitude station, have also been used to substantiate the TEC observations. The storm day TEC shows two well-defined humps at all stations wherein enhancements of the order of 80%–100% have been observed. While the first of the enhancements has been attributed to the prompt penetration electric field associated with an interplanetary electric field (IEF Ey) of about 35 mV/m, the other one has been attributed to the second episode of the prompt penetration electric field (IEF Ey ∼ 20 mV/m) and abnormal equatorial plasma fountain in late evening hours, respectively. During the unsteady ring current conditions when the IMF Bz was still southward, penetration of a westward electric field has been inferred. Two peaks in foF2 have been observed whose time of occurrence coincides with those of the humps in the low-latitude TEC. Results from stations having nearly the same magnetic latitude show that the ionospheric response, in terms of GPS TEC, to the prompt penetration electric fields is longitudinally independent. Formation of the first hump in TEC is progressively delayed in time from low to near-equatorial latitudes for stations in different magnetic latitudes along nearly the same longitude. However, its time of appearance at Diego Garcia, a station magnetically conjugate to Udaipur, is the same as that at Udaipur. The results also reveal the poleward expansion of the ionization anomaly due to the storm. Disturbance dynamoelectric fields have been inferred to be responsible for the suppressed plasma fountain, resulting in suppressed TEC values and equatorward contraction of the ionization anomaly on 25 August, compared to a reference quiet day.

Differing Impacts of Resolution Changes in Latitude and Longitude on the Midlatitudes in the LMDZ Atmospheric GCM

Abstract: This article examines the sensitivity of the Laboratoire de Meteorologie Dynamique Model with Zoom Capability (LMDZ), a gridpoint atmospheric GCM, to changes in the resolution in latitude and longitude, focusing on the midlatitudes. In a series of dynamical core experiments, increasing the resolution in latitude leads to a poleward shift of the jet, which also becomes less baroclinic, while the maximum eddy variance decreases. The distribution of the jet positions in time also becomes wider. On the contrary, when the resolution increases in longitude, the position and structure of the jet remain almost identical, except for a small equatorward shift tendency. An increase in eddy heat flux is compensated by a strengthening of the Ferrel cell. The source of these distinct behaviors is then explored in constrained experiments in which the zonal-mean zonal wind is constrained toward the same reference state while the resolution varies. While the low-level wave sources always increase with resolution in that case, there is also enhanced poleward propagation when increasing the resolution in longitude, preventing the jet shift. The diverse impacts on the midlatitude dynamics hold when using the full GCM in a realistic setting, either forced by observed SSTs or coupled to an ocean model. © 2011 American Meteorological Society.

Response of the equatorial ionosphere to the total solar eclipse of 22 July 2009 and annular eclipse of 15 January 2010 as observed from a network of stations situated in the Indian longitude sector

Abstract: . Dual-frequency GPS TEC monitors have been used to study the response of the ionosphere to the solar eclipses of 22 July 2009 and 15 January 2010. The receivers were located at three stations, Calcutta, Kharagpur and Baharampore which are situated outside the umbra zone in the Indian longitude sector with each baseline being ~200 km. Effects of obscuration of the solar disc were noted in the ambient TEC recorded at the three stations. A series of depletions in TEC along the track of a GPS satellite and associated wave-like structures were identified on some GPS links during both the eclipses.

Exoplanets transmission spectroscopy: accounting for eccentricity and longitude of periastron. Superwinds in the upper atmosphere of HD209458b?

Abstract: Context: Several studies have so far placed useful constraints on planetary atmospheric properties using transmission spectrsocopy, and in the case of HD209458b even the radial velocity of the planet during the transit event has been reconstructed opening a new range of possibilities. AIMS. In this contribution we highlight the importance to account for the orbital eccentricity and longitude of periastron of the planetary orbit to accurately interpret the measured planetary radial velocity during the transit. Methods: We calculate the radial velocity of a transiting planet in an eccentric orbit. Given the larger orbital speed of planets with respect to their stellar companions even small eccentricities can result in detectable blue or redshift radial velocity offsets during the transit with respect to the systemic velocity, the exact value depending also on the longitude of the periastron of the planetary orbit. For an hot-jupiter planet, an eccentricity of only e=0.01 can produce a radial velocity offset of the order of the km/s. Conclusions: We propose an alternative interpretation of the recently claimed radial velocity blueshift (~2 km/s) of the planetary spectral lines of HD209458b which implies that the orbit of this system is not exactly circular. In this case, the longitude of the periastron of the stellar orbit is most likely confined in the first quadrant (and that one of the planet in the third quadrant). We highlight that transmission spectroscopy allows not only to study the compositional properties of planetary atmospheres, but also to refine their orbital parameters and that any conclusion regarding the presence of windflows on planetary surfaces coming from transmission spectroscopy measurements requires precise known orbital parameters from RV.

Method and system for compressing location data of a radio for over-the-air transmission

Abstract: Disclosed are methods and systems for compressing location data of a radio for over-the-air transmission. A method includes obtaining raw latitude and raw longitude coordinates reflecting a current location of the client device, the raw latitude coordinate represented by x number of bits and the raw longitude coordinate represented by y number of bits. The raw latitude coordinate is truncated by removing n number of most significant bits from the raw latitude coordinate to create a compressed latitude coordinate. The raw longitude coordinate is truncated by removing m number of most significant bits from the raw longitude coordinate to create a compressed longitude coordinate, where m varies as a function of the value of the raw latitude coordinate. The compressed longitude and compressed latitude coordinates are then transmitted to another network device for decompression and use as an indication of the client device's absolute location.