Options for mapping foF2

1
Options for mapping foF2

• P A Bradley
• (Pandora, Scotlands Drive, Farnham Common, Slough
  SL2 3ES, UK)

2
Early foF2 studies for HF radio circuit planning
and operation

• Determination of MUF and field strength assuming
  great-circle propagation with mid-path or two
  control point foF2
• Active groups UK (Marconi), USA (NBS), Germany
  (Bundespost), France (CNET), Japan (Radio
  Research Labs.)
• Various representations of diurnal, seasonal,
  solar cycle and geographical changes
• - UT or LT
• - world or regional maps
• - geographic or magnetic latitude
• - each year separately or once-and-for-all maps
• - solar cycle or ionospheric indices (R12, ?,
  IF2)

3
Jones-Gallet foF2 mapping procedure adopted by
the CCIR in 1969 for international radio service
planning

• 24 separate reference world maps, one for each
  month for two high and low levels of solar
  activity (R12100 and 0)
• based on vertical-incidence ionosonde
  measurements for all available locations for
  1954, 1955 and 1964 (solar minimum) and 1956-58
  (solar maximum)
• mapping in UT and mixed geographic/magnetic
  latitude parameters
• given by spherical harmonic latitude and
  longitude functions with associated numerical
  coefficients

4
The Jones-Gallet functional representation

• foF2 (?, ?, T) SkU0,k Gk(?, ?, X) SH cos
  jTSk U2j,k.Gk(?, ?, X)
• sin jTSk U2j-1.Gk(?, ?, X)
• with ? geographic latitude
• ? geographic longitude
• T UT
• X mixed geographic/magnetic latitude
  parameter
• The functional form of G is determined by the
  value of k
• H is the maximum harmonic time order 6 and the
  Us are numerical coefficients
• k is chosen to minimise the RMS residual between
  measurements and representation leading to 488
  coefficients per map

5
WORLD MAPS OF MEDIAN foF2 (MHz) FROM CCIR
MODEL
6
Disquiet with the CCIR maps

• based on old years of data for highest ever solar
  cycle
• some southern hemisphere data points simulated
  from northern hemisphere with a seasonal flip
• no measurements over the oceans

7
URSI Mapping Working Group activities (1985-89)

• Charged to produce improved maps using
  thermospheric wind theory to simulate ocean data
  points
• Chose to retain Jones-Gallet mapping with same
  maximum harmonic orders as CCIR for
  compatibility with existing computer codes
• Minority view that higher-order harmonics should
  have been adopted(IPS alternative Fox/Wilkinson
  mapping)

8
Relative merits of CCIR and URSI maps

• maps can only be tested where there are
  measurement data ie over land
• CCIR maps test more accurate than URSI maps, but
  unproven feeling that over oceans URSI maps
  should be more accurate
• both available as an option in IRI computer code

9
Requirements for foF2 maps for HF propagation
studies

• Activity Service
  Circuit Circuit Frequency
  Planning Planning Diagnostics
  ManagementGlobal Average Past
  X X Maps Recent Past X X XRegion
  al Average Past X Maps Recent
  Past X Nowcast/Real Time X X

10
Requirements for foF2 maps for studies of
Earth-Space propagation effects and aeronomy
investigations

• Activity Service and
  Circuit Circuit Aeronomy Planning
  DiagnosticsGlobal Average
  Past X XMaps Recent Past X XRegiona
  l Average Past X X XMaps Recent
  Past X X X Nowcast/Real Time X X

11
Requirements for foF2 maps

• Conclusions
• Different requirements dictate the need for
  different maps
• The CCIR and URSI maps should not necessarily be
  seen as standards to compare with other maps

12
Latest ITU-R mapping proposals

• Digitise existing CCIR maps on a 2.5o
  latitude/longitude grid so available isolated
  measurements can replace once-and-for all values

13
Options for combining isolated measured foF2
values with background predictions

• Between equally spaced and smoothly varying
  grid-point values
• (i) replace the nearest predicted grid-point
  value with the measured value
• (ii) replace the nearest predicted grid-point
  value with a weighted average of the measured and
  predicted values
• (iii) smooth between measured and predicted
  values over a linear traverse within a buffer
  zone of arbitrary size providing gradient
  continuity (the COST238 solution)

14
What should the IRI (and COST296) now be doing in
foF2 mapping?

• Establish a Joint (?) Steering Group to
• - review available options and make
  recommendations for reference procedures that can
  be used to generate user-specific
• (i) global maps for future epoch radio-circuit
  planning,
• (ii) regional maps for past epochs, also
  incorporating
• available measured values
• - comment on the ITU-R proposals for adoption of
  grid-point values and the separations these
  should have, and
• - review the feasibility and possible
  geographical extent of additional foF2 values
  determined from GPS, and other navigational
  satellites, or from occultation observations, eg
  COSMIC