Fr. Hennessey, SJ on the ionospheric and magnetic stations of Manila Observatory in 1969

by Quirino Sugon Jr.

I am researching on the history of Manila Observatory’s ionosphere and magnetic research.  I found an article by Fr. Hennessey in Solar Physics, vol. 9, 496-501 (1969).  Some excerpts:

  • (a) Beginning January 1964 the ionosphere station was transferred from Baguio to a location about 2 miles north of the Central Observatory.  This is close enough for rapid data acquisition and remote enough to preven undue radio interference.  The ionosonde currently in use is a modified ESSA C-3 type with a C-4 receiver and transmitter.  Routinely ionograms are obtained continuously every 15 min with additional sweeps near the hour.  Reduction of data follows the procedures of Environmental Science Administration at Boulder, Colo. which sponsors this ionospheric work.
  • (b) Three sudden phase anomaly (SPA) circuits are regularly monitored.  These have proved to have a good corelation with larger flare activity.  The Rugby, Great Britain station transmits at 16 kHz; the station at Maine at 17.8 kHz has its transmission path very nearly across the North Pole; and the Seattle station sends at 18.6 kHz.  A solar flare causing a lowering of the ionosphere produces a phase shift in the received signal. These particular circuits taken together give a fair coverage of the entire globe.  Sudden enhancements of signal strength (SES) are recorded by the same SPA instruments.  Equipment for these observations has been supplied by ESSA at Boulder.
  • (c) Several radio circuits monitor effects of solar activity.  A riometer (on loan from AFCRL) continously receiving cosmic noise at 30 MHz shows the ionospheric absorption.  Sudden Cosmic Noise Absorption (SCNA) is also recorded with 18 MHz radiation.  At a lower frequency of 27 kHz Sudden Enhancements of Atmospherics (SEA) indicate solar effects.  Several short wave fadeout (SWF) circuits are in use for frequencies between 5 and 10 MHz.
  • (d) Changes in the earth’s magnetic field are recorded at three locations and serve as solar activity indicators.  AT the central station a Schonstedt HSM-1 Heliflux Station Magnetometer shows the variation in the Horizontal component of the field.  Both at Baguio (16.41 deg North Latitude and 120.63 deg East Longitude with a magnetic dip of 18 deg North) and at Dava0 (7.09 deg North Latitude and 125.57 deg East Longitude with a magnetic dip of 2 deg South) three components of the field are registered by means of Askania Magnetic Variometers.  QHM instruments at the same place provide absolute values for the H-field.  Since Davao is slightly south of the magnetic dip equator while both Manila and Bguio are well to the north of the equator, the variations are very indicative.  The Davao station has the further advantage of being under the equatorial electrojet.
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