Field-aligned currents inferred from low-altitude earth-orbiting satellites and ionospheric currents inferred from ground-based magnetometers - do they render consistent results? J. Watermann, F. Christiansen, P. Stauning, O. Rasmussen Danish Met

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GAFS Geomagnetic Activity Forecast a Service
for Prospectors and SurveyorsJ. Watermann (1),
H. Gleisner (1), T. Rasmussen (2), S. McCulloch
(3) (1) Danish Meteorological Institute,
Copenhagen, Denmark (2) Geological Survey
of Denmark and Greenland, Copenhagen,
Denmark (3) formerly Baker Hughes INTEQ
Scandinavia now Halliburton Noway, Sperry
Drilling Services
Synthesis The project objective has been the
development of a computer-based system for a
targeted geomagnetic activity forecast service.
The service consists of a brief description of
observed solar activity and current and expected
geomagnetic activity at selected sites together
with a graphical scheme displaying the level of
disturbance of the geomagnetic field expected
over the next three hours, the next 12 hours and
the next two days. The geomagnetic disturbance
level is scaled according to the geographic area
sub-auroral, auroral and polar cap latitudes
and according to specific user requirements. The
service is provided automatically and
continously. Automatically updated forecasts are
presented in detail on a restricted Web site, and
a summary of expected activity levels appear on
the publicly accessible web site http//www.dmi.dk
/projects/ESA_SWAPP/Public/magoutlook.shtml
Project manager Jurgen Watermann
(jfw_at_dmi.dk) Danish Meteorological
Institute Atmosphere Space Research Division

• Methodology
• A number of empirical models relating geomagnetic
  activity to the solar-wind conditions have been
  presented in the scientific literature. Using
  real-time solar wind data from the ACE spacecraft
  as input to a filter, e.g. a linear/nonlinear
  filter or a neural network, short-range
  geomagnetic forecasts (an hour ahead, although in
  GAFS this range is extended to 3 hours) can be
  made. In GAFS, we use a linear filter whose input
  consists of parameters that are non-linear
  functions of fundamental solar-wind observables.
• To go beyond a lead time of a few hours requires
  that we incorporate remote observations of the
  solar surface and the inner heliosphere into our
  forecast scheme. The solar sources of geomagnetic
  activity can schematically be separated into
  transient eruptive events and quasi-static
  recurrent structures roughly co-rotating with the
  Sun. In GAFS, we use earth-directed halo Coronal
  Mass Ejections (CMEs) observed by the LASCO
  instrument onboard the SOHO spacecraft and with
  interpretations provided by the NRL as the
  primary indicator of potentially geoeffective
  solar-wind disturbances over the next few days.
  From the fluxes of Solar Energetic Particles
  (SEPs) observed by the SEM instrument onboard the
  GOES geostationary satellites, the expected
  geoeffectiveness is quantified and an appropriate
  alert level is defined.
• In the absence of solar eruptive events we assume
  that the solar wind is governed by large-scale,
  quasi-static solar magnetic fields co-rotating
  with the Sun. Based on observations of solar
  surface magnetic fields, solar-wind models
  currently provide forecasts of solar wind
  velocity and the magnitude and direction of the
  inter-planetary magnetic field. From a
  statistical relationship between geomagnetic
  activity and the boundaries between low-speed and
  high-speed solar wind streams and IMF sectors,
  and using the solar wind forecasts provided by
  solar wind models, we forecast moderate
  geomagnetic activity beyond the short-range time
  scale of a few hours.
• The primary data sets which we use as input to
  our scheme can be organized into four categories
  
• remote sensing of the sun and solar corona
• data sources SOHO spacecraft and ground-based
  solar observatories
• modeled solar wind speed and interplanetary
  magnetic field direction
• data sources Hakamada-akasofu-Fry (HAF) solar
  wind model data
• in-situ sensing of the solar wind and
  interplanetary magnetic field
• data sources ACE and SOHO spacecraft
• in-situ sensing of solar X-ray and energetic
  proton flux in the magnetosphere
• data sources GOES satellites
• in-situ sensing of the magnetic variations at
  ground level
• data sources DMI ground-based magnetometers

Background The geomagnetic field is at all
times subject to temporal variations on a wide
range of time scales. They originate in solar
activity and solar variability of many different
forms including solar flares, coronal mass
ejections, solar wind sector boundaries and
coronal hole streams. The figure below (left)
gives an example of geomagnetic variations of
large amplitude observed during a severe (but not
extreme) geomagnetic storm at three sites located
on the east and west coasts of Greenland,
respectively (below right). The stations are
neighbours in the sense that no other
magnetometers were in operation in between them.
The magnetic variations shown in the figure are
uncorrelated. It is therefore not possible to
apply a-posteriori corrections for magnetic field
variations to those measurements which were taken
at a place somewhere in between these stations.
Such conditions prohibit spatial interpolation
between neighboring sites and render simultaneous
measurements from remote reference stations
useless. However, under different conditions the
spatial correlation of geomagnetic variations can
be much larger, and it is worth-while
interpolating between spaced observations in
order to estimate the local perturbation.
GAFS project scheme
The flow diagram outlines the structure and the
elements of the prediction scheme. The left hand
column lists the input data sources, the central
blocks summarize the elements of the prediction
algorithm which are currently under development
by the service provider (DMI), and the blocks on
the right hand side show the expected output
product designed for the service users (GEUS and
Baker Hughes INTEQ). The project will include a
performance analysis, prediction versus
observation, and an assessment of the costs
potentially being saved through the use of our
geomagnetic activity forecast service. Summaries
of the forecast and the performance evaluation
will be made available on our publicly accessible
web site.
Figure 1 left total geomagnetic field variations
during a strong but not extreme storm (Dst
109) right sites where the observations were
collected
Figure 3 Data flow and geomagnetic activity
forecast algorithms employed in the project

• Variations of such intensity can adversely affect
  any technical system which relies on local
  magnetic field measurements to be taken in the
  absence of significant geomagnetic variations.
  Users who are unaware of and thus unprepared for
  the imminent occurrence of major magnetic field
  disturbances may conduct operations which later
  turn out to have been useless and eventually a
  waste of time and resources.
• Our project attempts to address this problem
  through the development of a service which gives
  advance notice of increasing geomagnetic activity
  and thus enables the potentially affected users
  to plan and conduct their operations in a more
  cost-effective way.
• The project strives to address specifically the
  needs of
• oil companies which perform directional
  drilling controlled by magnetic field sensors
  close to the borehead
• magnetic survey enterprises which map
  magnetostatic anomalies for geological research
  and prospection
• The figure below shows the result from an
  aeromagnetic survey conducted in 1998 in an area
  at the west coast of Greenland (see section
  indicated by an arrow). The local magnetostatic
  deviations from the geomagnetic reference field
  span about 1000 nT peak-to-peak. In this example,
  the spatial magnetic field variations reach the
  same order of magnetic as the storm-time temporal
  variations displayed in the figure above. Under
  these conditions it is obviously not possible to
  conduct an aeromagnetic survey which can render
  useful measurements. Times during which magnetic
  storms are in progress have therefore to be
  avoided, I.e., no survey flights should be
  scheduled.

Figure 4 Publicly accessible project web site
showing a two-day forecast of magnetic activity
for the areas of Denmark and Greenland
The future of the forecast service
Figure 5 Theoretically possible levels of user
demands and service maintenance options
Figure 2 Sample results from a magnetostatic
anomaly survey carrtied out in southwest
Greenland. The color scale indicates a total
field span of ca 1000 nT between minimum and
maximum.