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      <title>Top Downloaded Articles This Week: Radio Science</title>
      <link>http://www.agu.org/contents/journals/ViewPublishedToday.do</link>
      <description><![CDATA[]]></description>
      <language>en-us</language>
      <copyright>AGU</copyright>
      <docs>http://blogs.law.harvard.edu/tech/rss</docs>
      <webMaster>webmaster@agu.org</webMaster>
      <item>
         <title>Phenomenology of transionospheric pulse pairs: Further observations</title>
         <link>http://dx.doi.org/10.1029/98RS02031</link>
         <description><![CDATA[We report on further observations of transionospheric pulse pairs (TIPPs), which are the most powerful transient radio signals observed by the Blackbeard broadband digital radio receiver on the ALEXIS satellite. The source of these signals is unknown but appears to be associated with thunderstorm activity. The signals do not resemble those reported for known lightning processes. We have previously reported observations of these events in the frequency band 28-95 MHz. In this paper we report observations of TIPPs in the 117- to 166-MHz band, with the subsatellite point situated over the contiguous United States. The main results are that the measured pulse parameter statistics are nearly the same as reported for the low-frequency events, with the exception that the pulse separation distribution is biased toward smaller values in the high-frequency observations. The radiated power does not drop off appreciably even at 166 MHz, which further constrains the possible size and timescale of the source(s). We also report results of experiments designed to measure the apparent reflectivity of dry, flat ground at frequencies around 100 MHz. We find that the apparent reflectivity can exceed 90%. This result helps to explain how the second pulse in a TIPP can have so much energy relative to the first.]]></description>
         <author>Robert S. Massey, Daniel N. Holden and Xuan-Min Shao</author>
         <category>Radio Science</category>
         <pubDate>33</pubDate>
      </item>
      <item>
         <title>The Low-Latitude Ionosphere Sensor Network: Initial results</title>
         <link>http://dx.doi.org/10.1029/2011RS004978</link>
         <description><![CDATA[The Low-Latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to nowcast the state and dynamics of the low-latitude ionosphere and to develop forecasts of the electric fields, densities, and equatorial spread F over the South American continent. The LISN observatory consists of three different types of instruments: GPS receivers, fluxgate magnetometers, and vertical incidence pulsed ionospheric radar (VIPIR) ionosondes. This report provides a succinct summary of recent observations obtained using the LISN GPS receivers and complemented with measurements from other instruments and GPS receivers that operate in South America. More specifically, the following are shown here: (1) observations of total electron content (TEC) enhancements that occur near local midnight, (2) maps of TEC perturbations associated with the passage of traveling ionospheric disturbances over South America, and (3) statistics of TEC depletions for 2 years of low solar activity. Near-midnight TEC enhancements consist of sudden increases in TEC that occur after sunset at low latitudes on 30% of the days. These TEC enhancements last for several hours and can have amplitudes between 1 and 50 TEC units. On 11–12 March 2011 the largest TEC enhancement was observed in South America at times when the Jicamarca incoherent scatter radar operated and observed peak densities above 106 el/cc at 300 km altitude. It is suggested that a combination of zonal electric fields and meridional neutral winds are able to redistribute the plasma along the field lines and create regions of enhanced TEC. Maps of TEC perturbations associated with the passage of gravity waves (GWs) over South America have been used to measure the phase velocity and direction of propagation of GWs. The large number of GPS receivers over South America has allowed us to record bubble events for every day during 2008 and 2009. It was found that the number of TEC depletion detections varies with a periodicity of 28 days. It is mentioned how these new observations and the installation of the last four VIPIR ionosondes will lead to new discoveries in the near future.]]></description>
         <author>C. E. Valladares and J. L. Chau</author>
         <category>Radio Science</category>
         <pubDate>47</pubDate>
      </item>
      <item>
         <title>Resolute Bay CADI ionosonde drifts, PolarDARN HF velocities, and cross polar cap potential</title>
         <link>http://dx.doi.org/10.1029/2011RS004947</link>
         <description><![CDATA[In this study, velocities measured by the Rankin Inlet and Inuvik PolarDARN HF radars over Resolute Bay (RB) are compared with measurements from the RB CADI ionosonde to investigate the consistency of the measurements. Two types of comparisons are performed: 1-D, where each PolarDARN radar line-of-sight velocity is plotted against CADI velocity projected onto appropriate radar beam, and 2-D, where the PolarDARN merged velocity is compared with the full CADI vector. In both cases, velocities were found to statistically agree. For the 1-D comparison, the velocities were comparable in ∼85% of cases. For the 2-D comparison, a minor tendency for larger PolarDARN merge velocities (∼60 m/s) was noticed. The second task performed is a comparison of the SuperDARN cross polar cap potential (CPCP) and the CADI-based CPCP and their dependence on the CADI velocity. Linear dependences were found allowing for inter-conversion between these parameters. For large plasma drifts, the SuperDARN CPCPs were found to be much smaller than the CADI-based CPCPs hinting that the separation between the foci of a large-scale convection pattern is often underestimated in the SuperDARN convection mapping.]]></description>
         <author>D. Mori, A. V. Koustov, P. T. Jayachandran and N. Nishitani</author>
         <category>Radio Science</category>
         <pubDate>47</pubDate>
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      <item>
         <title>Introducing a disturbance ionosphere index</title>
         <link>http://dx.doi.org/10.1029/2011RS004939</link>
         <description><![CDATA[Although ionospheric perturbations such as traveling ionospheric disturbances have a strong impact on Global Navigation Satellite Systems (GNSS) and other space-based radio systems, the description of individual perturbations is difficult. To overcome this problem, it is suggested to use a disturbance ionosphere index (DIX) that describes the perturbation degree of the ionosphere in a less specific form as a proxy. Although such an index does not describe the exact propagation conditions at the measurement site, the estimated index number indicates the probability of a potential impact on radio systems used in communication, navigation, and remote sensing. The definition of such a DIX must take into account the following major requirements: relevance to practical needs, objective measure of ionospheric conditions, easy and reproducible computation, and availability of a reliable database. Since the total electron content has been shown in many publications to act as an outstanding parameter for quantifying the range error and also the strength of ionospheric perturbations, we propose a DIX that is based on GNSS measurements. To illustrate the use of the index, recent storms monitored in 2011 and the Halloween storm are discussed. The proposed index is a robust and objective measure of the ionospheric state, applicable to radio systems which are impacted by a highly variable perturbed ionosphere.]]></description>
         <author>N. Jakowski, C. Borries and V. Wilken</author>
         <category>Radio Science</category>
         <pubDate>47</pubDate>
      </item>
      <item>
         <title>First simultaneous measurement of vertical air velocity, particle fall velocity, and hydrometeor sphericity in stratiform precipitation: Results from 47 MHz wind-profiling radar and 532 nm polarization lidar observations</title>
         <link>http://dx.doi.org/10.1029/2011RS004823</link>
         <description><![CDATA[Results from simultaneous measurements of vertical air velocity (W), particle fall velocity, and hydrometeor sphericity in stratiform precipitation are reported for the first time. Cases of stratiform precipitation on 8 (case A) and 16 December 2008 (case B) observed at Sumatra, Indonesia (0.2°S, 100.32°E), are described. A 47 MHz wind-profiling radar measured W and reflectivity-weighted particle fall velocity relative to the air (VZ) simultaneously. Upward W above ∼6.0 km altitude in case B (>0.2 m s−1) was greater than in case A (<0.1 m s−1). VZ at 300 m above the 0°C altitude in case B (1.8 m s−1) was greater than in case A (1.3 m s−1). The thickness of melting layer (ML) in case B (900 m) was greater than in case A (300 m). Because the large-sized aggregates contribute to produce greater VZ and thicker ML, it is likely that entangled growth of dendritic crystals under the presence of significant upward W and enhanced aggregation occurrence by the well-developed dendritic crystals produced the large-sized aggregates. Lidar measured an increase of linear depolarization ratio (δ) and lidar dark band in the ML. Volume δ of raindrops was 0.08–0.10 in case B and close to zero in case A. Stronger multiple scattering in case B is likely a cause that produced the greater δ. In case B, a dip of δ was measured at the bottom of ML. The decrease of hydrometeor nonsphericity at the final stage of melting explains the dip.]]></description>
         <author>Tomoaki Mega, Masayuki K. Yamamoto, Makoto Abo, Yasukuni Shibata, Hiroyuki Hashiguchi, Noriyuki Nishi, Toyoshi Shimomai, Yoshiaki Shibagaki, Mamoru Yamamoto, Manabu D. Yamanaka, Shoichiro Fukao and Timbul Manik</author>
         <category>Radio Science</category>
         <pubDate>47</pubDate>
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