scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Characteristics of Intense Space Weather Events as Observed with GPS from a Low
Latitude Station
Paul Ashik 1 , DasGupta Ashish 2
1 Institute of Radio Physics and Electronics, University of Calcutta, Calcutta, India, 2 S.K. Mitra
Center for Research in Space Environment, University of Calcutta, Calcutta, India
Space Weather, a relatively new terminology, loosely defines the hierarchy of all phenomena
within the Sun-Earth environment that may impact systems that reside within that
environment. The Earth's ionosphere acts as a perturbing medium on transionospheric radio
signals coming from a radio source or a satellite. Scintillations of transionospheric signals
constitute one of the most intense Space Weather related propagation effects. Phase
scintillation measurements have been few over the world and no records of GPS phase
scintillations during intense Space Weather events have been reported from the geophysically
sensitive Indian longitude sector. A dual frequency high resolution software based GPS
receiver capable of measuring TEC with an accuracy of 5×10 -4 TEC units and providing phase
of the GPS L1 and L2 signals is operated round the clock at the Institute of Radio Physics and
Electronics (IRPE), University of Calcutta, Calcutta, India. GPS TEC sampled at 1 minute
interval and phase measurements at 17 Hz have been simultaneously monitored using this
receiver for studying some Space Weather events during 2008-2009, a period of extremely
low solar activity level, when post-sunset scintillations were observed on GPS links from
Calcutta (22.58 o N, 88.38 o E geographic; magnetic dip: 32 o N) situated virtually underneath
the northern crest of the Equatorial Ionization Anomaly. Data from a dual frequency
Ionospheric TEC and Scintillation Monitor operational at IRPE under the international
SCINDA program of the US Air Force was used in conjunction with the software based
receiver for studying the S4 indices on different GPS links mapped on a polar plot. On
February 2, 2008, the GPS SV16 link located almost due south of Calcutta exhibited
fluctuations in CNO with a maximum of 6 dB-Hz and associated bite-outs of nearly 15 TEC
units around 1540 UT. Patches of scintillations were noted on the amplitude (maximum
S4~0.5) and phase of the GPS L1 signal around the same time. On October 8, 2009, GPS
SV12 link located south of Calcutta exhibited sharp depletions in TEC during 1330-1415 UT.
CNO fluctuations of about 10 dB-Hz were noted at 1350 UT on GPS L1 frequency. Welldefined
patches of phase scintillations occurred during 1340-1440 UT. The amplitude
scintillation patches were intense with maximum S4~0.6 at 1340 UT. This paper presents
some cases of intense Space Weather events occurring in the equatorial latitudes even under
magnetically quiet conditions and low solar activity levels.