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Browsing Monografías by Subject "Atmosphere"
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Item Restricted Observations of TIDs over South and Central America(American Geophysical Union, 2016-11-18) Valladares, Cesar E.; Sheehan, Robert; Pacheco, Edgardo E.TEC values measured by GPS receivers that belong to the low‐latitude ionosphere sensor network (LISN) and several other networks that operate in South and Central America were used to study the characteristics and origin of traveling ionospheric disturbances (TID) in these regions. The TEC perturbations associated with these TIDs show a high degree of spatial coherence over distances > 1000 km allowing us to use measurements from receivers spaced by hundreds of km to calculate the TIDs' travel velocities, propagation direction, and scale size. We first applied the TID analysis to TEC measurements corresponding to 4 July 2011. This processing method is then used to study the characteristics of TIDs for 20 and 21 August 2011, a period when a tropical storm was active in the Caribbean region. A pronounced increase in TID activity was observed in South and Central America at 16 UT on 20 August 2011 lasting until the end of 21 August 2011. The TID velocities show a very variable pattern that depends upon their local time and location. Counter‐streaming TIDs were observed over the western part of South America on 21 August 2011. Regional maps of tropospheric temperature brightness, measured by the GOES‐12 satellite, are used to identify and follow the development of the tropical storm (TS) Irene and several deep convective plumes. TIDs were observed propagating away from TS Irene. This storm moved into the Caribbean region and intensified earlier on 20 August spawning a train of atmospheric gravity waves (AGW). The small scale size, the velocity less than 150 m/s, and the close location of several TIDs with respect to TS Irene indicate that these TIDs may be the result of primary AGWs that reached the F‐region bottomside. These results open the possibility of using TEC values measured by networks of GPS receivers to construct regional, and probably global, maps of TIDs, identify their origin, and study in detail the characteristics of TIDs corresponding to primary and secondary AGWs.Item Open Access Radar/ MST and ST radars and wind profilers(Academic Press, 2002-12) Woodman Pollitt, Ronald FranciscoTo qualify as an MST radar, the system has to be capable of obtaining echoes from the mesosphere. This requirement limits the frequency range of these radars to the lower frequencies of the VHF band, i.e., between 30 and 300 MHz. Smaller radars, using the same principles and techniques but capable of reaching only the stratosphere and troposphere, are called ST radars. Here we can cite as an example the NOAA Tropical Pacific Profiler Network in the equatorial Pacific, and the wind profiler network in central United States as important multiple radar installations that qualify as such. These, and even smaller systems capable of observing only the troposphere, are also called wind profilers, because of their main use as operacional radars dedicated to measuring the winds aloft in a continuous manner. At these lower altitudes it is possible to use frequencies higher than VHF frequencies. Nowadays, many radars designed for other purposes, including operational air traffic, meteorological Doppler radars, and ionospheric incoherentscatter radars, are also used as ST radars.