A new methodology for the development of high-latitude ionospheric climatologies and empirical models

Many empirical models and climatologies of high-latitude ionospheric processes, such as convection, have been developed over the last 40 years. One common feature in the development of these models is that measurements from different times are combined and averaged on fixed coordinate grids. This methodology ignores the reality that high-latitude ionospheric features are organized relative to the location of the ionospheric footprint of the boundary between open and closed geomagnetic field lines (OCB). This boundary is in continual motion, and the polar cap that it encloses is continually expanding and contracting in response to changes in the rates of magnetic reconnection at the Earth's magnetopause and in the magnetotail. As a consequence, models that are developed by combining and averaging data in fixed coordinate grids heavily smooth the variations that occur near the boundary location. Here we propose that the development of future models should consider the location of the OCB in order to more accurately model the variations in this region. We present a methodology which involves identifying the OCB from spacecraft auroral images and then organizing measurements in a grid where the bins are placed relative to the OCB location. We demonstrate the plausibility of this methodology using ionospheric vorticity measurements made by the Super Dual Auroral Radar Network radars and OCB measurements from the IMAGE spacecraft FUV auroral imagers. This demonstration shows that this new methodology results in sharpening and clarifying features of climatological maps near the OCB location. We discuss the potential impact of this methodology on space weather applications

Mapping ionospheric backscatter measured by the SuperDARN HF radars - Part 1: A new empirical virtual height model

Accurately mapping the location of ionospheric backscatter targets (density irregularities) identified by the Super Dual Auroral Radar Network (SuperDARN) HF radars can be a major problem, particularly at far ranges for which the radio propagation paths are longer and more uncertain. Assessing and increasing the accuracy of the mapping of scattering locations is crucial for the measurement of two-dimensional velocity structures on the small and meso-scale, for which overlapping velocity measurements from two radars need to be combined, and for studies in which SuperDARN data are used in conjunction with measurements from other instruments. The co-ordinates of scattering locations are presently estimated using a combination of the measured range and a model virtual height, assuming a straight line virtual propagation path. By studying elevation angle of arrival information of backscatterred signals from 5 years of data (1997-2001) from the Saskatoon SuperDARN radar we have determined the actual distribution of the backscatter target locations in range-virtual height space. This has allowed the derivation of a new empirical virtual height model that allows for a more accurate mapping of the locations of backscatter targets

Estimating the location of the open-closed magnetic field line boundary from auroral images

The open-closed magnetic field line boundary (OCB) delimits the region of open magnetic flux forming the polar cap in the Earth’s ionosphere. We present a reliable, automated method for determining the location of the poleward auroral luminosity boundary (PALB) from far ultraviolet (FUV) images of the aurora, which we use as a proxy for the OCB. This technique models latitudinal profiles of auroral luminosity as both a single and double Gaussian function with a quadratic background to produce estimates of the PALB without prior knowledge of the level of auroral activity or of the presence of bifurcation in the auroral oval. We have applied this technique to FUV images recorded by the IMAGE satellite from May 2000 until August 2002 to produce a database of over a million PALB location estimates, which is freely available to download. From this database, we assess and illustrate the accuracy and reliability of this technique during varying geomagnetic conditions. We find that up to 35% of our PALB estimates are made from double Gaussian fits to latitudinal intensity profiles, in preference to single Gaussian fits, in nightside magnetic local time (MLT) sectors. The accuracy of our PALBs as a proxy for the location of the OCB is evaluated by comparison with particle precipitation boundary (PPB) proxies from the DMSP satellites. We demonstrate the value of this technique in estimating the total rate of magnetic reconnection from the time variation of the polar cap area calculated from our OCB estimates

An investigation of latitudinal transitions in the SuperDARN Doppler spectral width parameter at different magnetic local times

International audienceLatitudinal transitions from low to high Doppler spectral width in backscatter measured by the Super Dual Auroral Radar Network (SuperDARN) are now routinely used as proxies for the polar cap boundary (PCB) in the cusp-region ionosphere. In this paper we perform a statistical study of the nature of similar spectral width transitions at other magnetic local times (MLTs). This analysis illustrates that these latitudinal spectral width transitions exist at all magnetic local times, and that the latitude, gradient, and amplitude of the transitions vary systematically with MLT. In particular, the probability of a transition occurring at any latitude, identified independently in each MLT sector, is continuous with MLT from the cusp, through the morning sector, to the nightside. This suggests that the transition represents the PCB, as this is known to be what it represents in the cusp region. However, the picture in the afternoon sector (12:00-18:00 MLT) is more complex with no clearly preferred transition latitudes. Key words. Ionosphere (ionosphere-magnetosphere interactions; instruments and techniques). Magnetospheric physics (magnetopause, cusp, and boundary layers.

Magnetic local time variation and scaling of poleward auroral boundary dynamics

The balance of dayside and nightside reconnection processes within the Earth's magnetosphere, and its effect on the amount of open magnetic flux threading the ionosphere is well understood in terms of the expanding-contracting polar cap model. However, the nature and character of the consequential fluctuations in the polar cap boundary are poorly understood. By using the poleward auroral luminosity boundary (PALB), as measured by the FUV instrument of the IMAGE spacecraft, as a proxy for the polar cap boundary we have studied the motion of this boundary for more than two years across the complete range of magnetic local time. Our results show that the dayside PALB dynamics are broadly self-similar on timescales of 12 minutes to 6 hours and appear to be monofractal. Similarity with the characteristics of solar wind and interplanetary magnetic field (IMF) variability suggest that this dayside monofractal behaviour is predominantly inherited from the solar wind via the reconnection process. The nightside PALB dynamics exhibit scale-free behaviour at intermediate timescales (12-90 minutes) and appear to be multifractal. We propose that this character is a result of the intermittent multifractal structure of magnetotail reconnection

Solar-wind-driven geopotential height anomalies originate in the Antarctic lower troposphere

We use National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data to estimate the altitude and time lag dependence of the correlation between the interplanetary magnetic field component, By, and the geopotential height anomaly above Antarctica. The correlation is most statistically significant within the troposphere. The peak in the correlation occurs at greater time lags at the tropopause (∼6–8 days) and in the midtroposphere (∼4 days) than in the lower troposphere (∼1 day). This supports a mechanism involving the action of the global atmospheric electric circuit, modified by variations in the solar wind, on lower tropospheric clouds. The increase in time lag with increasing altitude is consistent with the upward propagation by conventional atmospheric processes of the solar wind-induced variability in the lower troposphere. This is in contrast to the downward propagation of atmospheric effects to the lower troposphere from the stratosphere due to solar variability-driven mechanisms involving ultraviolet radiation or energetic particle precipitation

Comment on "Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities" by K.-H. Glassmeier et al., Ann. Geophysicae, 17, 338-350, (1999)

International audienceNot availabl

CDAOStore: A Phylogenetic Repository Using Logic Programming and Web Services

The CDAOStore is a portal aimed at facilitating the storage and retrieval of data and metadata associated to studies in the field of evolutionary biology and phylogenetic analysis. The novelty of CDAOStore lies in the use of a semantic-based approach to the storage and querying of data. This enables CDAOStore to overcome the data format restrictions and complexities of other repositories (e.g., TreeBase) and to provide a domain-specific query interface, derived from studies of querying requirements for phylogenetic databases. CDAOStore represents the first full implementation of the EvoIO stack, an inter-operation stack composed of a formal ontology (the Comparative Data Analysis Ontology), an XML exchange format (NeXML), and a web services API (PhyloWS). CDAOStore has been implemented on top of an RDF triple store, using a combination of standard web technologies and logic programming technology. In particular, we employed Prolog to support some of the format transformation tasks and, more importantly, in the implementation of several of the domain-specific queries, whose structure is beyond the reach of standard RDF query languages (e.g., SPARQL). CDAOStore is operational and it already hosts over 90 million RDF triples, imported from TreeBase or submitted by other domain scientists

F-region ionosphere effects on the mapping accuracy of SuperDARN HF radar echoes

Structured particle precipitation in the cusp is an important source for the generation of F-region ionospheric irregularities. The equatorward boundaries of broad Doppler spectral width in Super Dual Auroral Radar Network (SuperDARN) data and the concurrent OI 630.0 nm auroral emission are good empirical proxies for the dayside open-closed field line boundary (OCB). However, SuperDARN currently employs a simple virtual model to determine the location of its echoes, instead of a direct calculation of the radio wave path. The varying ionospheric conditions could influence the final mapping accuracy of SuperDARN echoes. A statistical comparison of the offsets between the SuperDARN Finland radar spectral width boundary (SWB) and the OI 630.0 nm auroral emission boundary (AEB) from a meridian-scanning photometer (MSP) on Svalbard is performed in this paper. By restricting the location of the 630.0 nm data to be near local zenith where the MSP has the highest spatial resolution, the optical mapping errors were significantly reduced. The variation of the SWB – AEB offset confirms that there is a close relationship between the mapping accuracy of the HF radar echoes and solar activity. The asymmetric variation of the SWB – AEB offset versus magnetic local time suggests that the intake of high density solar extreme ultraviolet ionized plasma from post-noon at sub-auroral latitudes could result in a stronger refraction of the HF radar signals in the noon sector. While changing the HF radar operating frequency also has a refraction effect that contributes to the final location of the HF radar echoes