Space Weather Euro News Vol.4 Issue 2 (07-01-2000)
Table of Contents:
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1. Effect of leap seconds on space physics coordinate
transformations
2. IRInfo No. 18
3. Some ESA Tender Actions
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Send all contributions to:
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1. Effect of leap seconds on space physics coordinate
transformations
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From: Mike Hapgood E-mail: M.A.Hapgood@rl.ac.uk
I enclose below a copy of a questionaire from an URSI Commission J Working
Group that is investigating the future use of leap seconds in the definition
of Coordinated Universal Time (UTC). This issue may be of interest to many
in the space physics community because it impacts on the co-ordinate
transformations that we use. This arises because Universal Time (UT1) is a
measure of the spin phase of the Earth. Thus it is a key factor in
transformations from inertial co-ordinates (as used to represent spacecraft
orbits) to co-ordinate systems spinning with the Earth, e.g. geocentric and
geodetic co-ordinates plus any system based on the geomagnetic dipole - such
as geocentric-solar-magnetospheric and solar-magnetic co-ordinates. (But
note that it does not impact on the transformations from inertial
co-ordinates to geocentric-solar-ecliptic coordinates.)
Leap seconds are used to keep UTC (based on atomic clocks) within 0.9
seconds of UT1 (measured from the spin phase of the Earth). Given that the
Earth rotates by 13.5 seconds of arc in 0.9 seconds, the difference between
UT1 and UTC amounts to a spin phase error of less than 6.5e-5 radians, which
is equivalent to a position error of less than 3 km at geosynchronous orbit.
Thus we have been able to neglect the difference between UTC and UT1, and
substitute UTC for UT1 in space physics co-ordinate transformations.
If use of leap seconds were to cease (and there may be significant pressure
for this because leap seconds cause problems for important applications such
as global positioning systems), the difference between UTC and UT1 would
then increase at about 0.7 seconds per year. Thus the space physics
community would gradually need to include the correction from UTC to UT1 in
its co-ordinate transformations.
If you wish to comment on this issue, please complete the questionnaire
below and return it to the Demetrios Matsakis at the US Naval Observatory
(address at end of questionnaire).
For those of you who wish just to monitor this issue, I have included (and
will update as appropriate) details on my space physics co-ordinate
transformations web site
(http://sspg1.bnsc.rl.ac.uk/Share/Coordinates/ct_home.htm).
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Questionnaire from an URSI Commission J Working Group
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Dear Project Manager or Scientist,
It is being proposed to change the definition of Coordinated Universal
Time (UTC) regarding the insertion of leap-seconds, possibly even
eliminating their use. The issue has been discussed in several
timekeeping forums, and published in the Innovations Section of the
November, 1999 issue of GPS World.
Leap seconds are introduced so as to keep UTC synchronized (within 0.9 s)
to the time scale determined from the Earth's rotation. Should no new
leap seconds be inserted, solar time will diverge from atomic time at
the rate of about 2 seconds every 3 years, and after about a century
|UT1-UTC| would exceed 1 minute. Although no fundamental problems are
anticipated, it is very likely that Y2K-like problems may result in
software that assumes UT1=UTC, or |UT1-UTC|< some value, or whose
input/output records use a field size that can only accommodate
|UT1-UTC| values up to one second.
To gather information, an URSI Commission J Working Group was formed,
consisting of Don Backer, Wim. N. Brouw, Barry Clark, Irwin Shapiro,
Ir. E. Van Lil, and myself.
We would like to ask you to consult with the members of your institute
who currently deal with UT1-UTC, and give us a considered response to
the following two questions:
A. If the appropriate international bodies decide to eliminate the
insertion of new leap seconds, would you foresee any practical problems
for your institution/instrument/observations?
no ____
* yes ___
* possibly ____
(* please explain any known or possible problems, but
if posible
try to answer in ascii text instead
of an attachment)
B. Would you be in favor of such a proposal?
yes ____
no ____
indifferent ___
have better idea ___
(feel free to comment)
C. Is there anyone else you would recommend we contact?
(feel free to forward this email directly)
I would appreciate your assistance, and a response by January 15 to
dnm@orion.usno.navy.mil.
This questionnaire was first sent to the URSII national representatives,
a list of 931 astronomical institutions maintained by the American
Astronomical Society, and 125 prominent scientists. It has since sent
sent to several mailing lists associated with Earth rotation. I would
like to apologize to anyone contacted twice, but also appreciate it if
you would forward this email to anyone we may have missed. We will
tabulate all responses, and are particularly interested in quantitative
estimates from people whose systems can not easily accommodate the change.
Technology permitting, I will also email the report to all who have
responded.
Sincerely,
Demetrios Matsakis
______________________________________________________
Dr. Demetrios N.
Matsakis Director, Time
Service Department
(202) 762-1587 DSN 762-1587
U. S. Naval Observatory
FAX (202)
762-1511
3450 Massachusetts Avenue NW
dnm@orion.usno.navy.mil
Washington DC, USA 20392-5420
_______________________________________________________
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2. IRInfo No. 18
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From: Dieter Bilitza E-mail: bilitza@gsfc.nasa.gov
*** International
Reference Ionosphere ***
***IRInfo No. 18 ***
January 5, 2000
__________________________________________________________
1) CALL FOR PAPERS: COSPAR Session on Modeling the Topside
Ionosphere and Plasmasphere
CALL FOR PAPERS: COSPAR Session on Modeling the Topside
Ionosphere and Plasmasphere
33rd COSPAR Scientific Assembly Warsaw, Poland, 16-23 July 2000
Abstract deadline: 10 January 2000 (please send copy to the main
scientific organizer) http://www.copernicus.org/COSPAR/COSPAR.html
Session Number: C4.1/D3.9 (currently scheduled for Tuesday and
Wednesday of the COSPAR week)
Session Description: This is a joint meeting of COSPAR Commissions C
and D. The meeting is organized by the URSI/COSPAR Working Group on
the International Reference Ionosphere (IRI). The objective is to review the
status of topside and plasmaspheric modeling and to establish improved
models for inclusion in IRI. Empirical and theoretical papers are welcome.
We will also accept papers that deal with improvements of IRI parameters
in areas other than the topside/plasmasphere. The organizing team strongly
encourages contributions that describe applications of the IRI model. The
session will include solicited, contributed and poster papers.
Main Scientific Organizer: Dr. Dieter Bilitza National Space Science Data
Center GSFC/Raytheon ITSS Code 632 Greenbelt, MD 20771, USA
phone: (301) 286-0190 FAX: (301) 286-1771 Email:
dieter.bilitza@gsfc.nasa.gov
Deputy Organizer: Dr. Iwona Stanislawska Space Research Centre of
Polish Academy of Sciences 00-716 Warsaw Ul.Bartycka 18a POLAND
tel: +(48) (22) 8403766 ext. 381 fax: +(48) 39 121273 e-mail:
stanis@cbk.waw.pl
Organizing Committee: I. Stanislawska, D. Bilitza, B. Reinisch, K. Oyama,
K. Rawer
2) C-version of IRI
We thank Ari Edinburg (MSc Electronic Engineering, Software Now cc,
Johannesburg, South Africa) for submitting a new C-code version of IRI.
The files are available from the IRI ftp site at nssdc.gsfc.nasa.gov in
directory models/ionospheric/iri/iri95/c_code/Dec_99/.
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3. Some ESA Tender Actions
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For more information and the complete list of ESA Tender Actions
please look at:
http://emits.esa.int/emits/OpenTenders
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Note: This newsletter is an initiative of the
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Maurizio Candidi, CNR
Paul Cannon, URSI-Commission G
Mike Hapgood, EGS
Hannu Koskinen, SCOSTEP working group on Space weather
Pierre Lantos, ISES
Henrik Lundstedt, Lund space weather center
Goetz Paschmann, ISSI
Jean-Yves Prado, CNES-ONERA working group on space weather
Michael Rycroft, ISU
Volker Bothmer, EGS-Solar Physics Secretary
Wolfgang Baumjohann, MPE-German Representative
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