Earth's rotational velocity is not constant over time. Any motion of mass in or on Earth causes a slowdown or speedup of the rotation speed, or a change of rotation axis. Small motions produce changes too small to be measured, but movements of very large mass, like sea currents, tides, or those resulting from earthquakes, can produce discernible changes in the rotation and can change very precise astronomical observations. Global simulations of atmosphere, ocean, and land dynamics are used to create effective angular momentum (EAM) functions that can be used to predict changes in EOP.[1]
Universal time (UT1) tracks the Earth's rotation in time, which performs one revolution in about 24 hours. The Earth's rotation is uneven, so UT is not linear with respect to atomic time. It is practically proportional to the sidereal time, which is also a direct measure of Earth rotation. The excess revolution time is called length of day (LOD). The absolute value of UT1 can be determined using space geodetic observations, such as Very Long Baseline Interferometry and Lunar laser ranging, whereas LOD can be derived from satellite observations, such as GPS, GLONASS, Galileo[2] and Satellite laser ranging to geodetic satellites.[3][4] LOD is changing due to gravitational effects from external bodies and geophysical processes occurring in different Earth layers. Then, the LOD prediction is extremely difficult due to extreme events such as El Niño which demonstrated themselves in the LOD signals.[5]
Coordinates of the poleedit
Due to the very slow pole motion of the Earth, the Celestial Ephemeris Pole (CEP, or celestial pole) does not stay still on the surface of the Earth. The Celestial Ephemeris Pole is calculated from observation data, and is averaged, so it differs from the instantaneous rotation axis by quasi-diurnal terms, which are as small as under 0.01" (see [6]). In setting up a coordinate system, a static terrestrial point called the IERS Reference Pole, or IRP, is used as the origin; the x-axis is in the direction of IRM, the IERS Reference Meridian; the y-axis is in the direction 90 degrees West longitude. x and y are the coordinates of the CEP relative to the IRP. Pole coordinates can be determined using various space geodesy and satellite geodesy techniques, e.g., Satellite laser ranging, Very Long Baseline Interferometry, however, the most accurate techniques are GPS, GLONASS, and Galileo.[7]
Celestial pole offsetsedit
Celestial pole offsets are described in the IAUPrecession and Nutation models. The observed differences with respect to the conventional celestial pole position defined by the models are monitored and reported by the IERS. Celestial pole offsets can only be obtained by the VLBI. The observed CPO can quantify the deficiencies of the IAU2006/2000A precession–nutation model, including the astronomically forced nutations and a component of nutation that is considered unpredictable. Some studies indicate that substantial FCN (Free Core Nutation) amplitude and phase disturbances occurred at the epochs close to the revealed GMJ (Geomagnetic Jerk) events.[8][9]
Referencesedit
^Dobslaw, Henryk; Dill, Robert (February 2018). "Predicting Earth orientation changes from global forecasts of atmosphere-hydrosphere dynamics". Advances in Space Research. 61 (4): 1047–1054. Bibcode:2018AdSpR..61.1047D. doi:10.1016/j.asr.2017.11.044.
^Zajdel, Radosław; Sośnica, Krzysztof; Bury, Grzegorz; Dach, Rolf; Prange, Lars (July 2020). "System-specific systematic errors in earth rotation parameters derived from GPS, GLONASS, and Galileo". GPS Solutions. 24 (3): 74. doi:10.1007/s10291-020-00989-w.
^Zajdel, R.; Sośnica, K.; Drożdżewski, M.; Bury, G.; Strugarek, D. (November 2019). "Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS". Journal of Geodesy. 93 (11): 2293–2313. Bibcode:2019JGeod..93.2293Z. doi:10.1007/s00190-019-01307-0.
^Sośnica, K.; Bury, G.; Zajdel, R. (16 March 2018). "Contribution of Multi‐GNSS Constellation to SLR‐Derived Terrestrial Reference Frame". Geophysical Research Letters. 45 (5): 2339–2348. Bibcode:2018GeoRL..45.2339S. doi:10.1002/2017GL076850. S2CID 134160047.
^Modiri, S.; Belda, S.; Hoseini, M.; Heinkelmann, R.; Ferrándiz, Jose M.; Schuh, H. (February 2020). "A new hybrid method to improve the ultra-short-term prediction of LOD". Journal of Geodesy. 94 (23): 23. Bibcode:2020JGeod..94...23M. doi:10.1007/s00190-020-01354-y. PMC7004433. PMID 32109976.
^Zajdel, Radosław; Sośnica, Krzysztof; Bury, Grzegorz; Dach, Rolf; Prange, Lars; Kazmierski, Kamil (January 2021). "Sub-daily polar motion from GPS, GLONASS, and Galileo". Journal of Geodesy. 95 (1): 3. Bibcode:2021JGeod..95....3Z. doi:10.1007/s00190-020-01453-w.
^Modiri, Sadegh; Heinkelmann, Robert; Belda, Santiago; Malkin, Zinovy; Hoseini, Mostafa; Korte, Monika; Ferrándiz, José M.; Schuh, Harald (November 2021). "Towards Understanding the Interconnection between Celestial Pole Motion and Earth's Magnetic Field Using Space Geodetic Techniques". Sensors. 21 (22): 7555. Bibcode:2021Senso..21.7555M. doi:10.3390/s21227555. PMC8621431. PMID 34833631.
^Malkin, Zinovy; Belda, Santiago; Modiri, Sadegh (August 2022). "Detection of a New Large Free Core Nutation Phase Jump". Sensors. 22 (16): 5960. Bibcode:2022Senso..22.5960M. doi:10.3390/s22165960. PMC9414530. PMID 36015720.
earth, orientation, parameters, geodesy, astrometry, earth, orientation, parameters, describe, irregularities, rotation, planet, earth, provide, rotational, transform, from, international, terrestrial, reference, system, itrs, international, celestial, referen. In geodesy and astrometry earth orientation parameters EOP describe irregularities in the rotation of planet Earth EOP provide the rotational transform from the International Terrestrial Reference System ITRS to the International Celestial Reference System ICRS or vice versa as a function of time Earth s rotational velocity is not constant over time Any motion of mass in or on Earth causes a slowdown or speedup of the rotation speed or a change of rotation axis Small motions produce changes too small to be measured but movements of very large mass like sea currents tides or those resulting from earthquakes can produce discernible changes in the rotation and can change very precise astronomical observations Global simulations of atmosphere ocean and land dynamics are used to create effective angular momentum EAM functions that can be used to predict changes in EOP 1 Contents 1 Components 1 1 Universal time 1 2 Coordinates of the pole 1 3 Celestial pole offsets 2 References 3 External linksComponents editUniversal time edit Universal time UT1 tracks the Earth s rotation in time which performs one revolution in about 24 hours The Earth s rotation is uneven so UT is not linear with respect to atomic time It is practically proportional to the sidereal time which is also a direct measure of Earth rotation The excess revolution time is called length of day LOD The absolute value of UT1 can be determined using space geodetic observations such as Very Long Baseline Interferometry and Lunar laser ranging whereas LOD can be derived from satellite observations such as GPS GLONASS Galileo 2 and Satellite laser ranging to geodetic satellites 3 4 LOD is changing due to gravitational effects from external bodies and geophysical processes occurring in different Earth layers Then the LOD prediction is extremely difficult due to extreme events such as El Nino which demonstrated themselves in the LOD signals 5 Coordinates of the pole edit Due to the very slow pole motion of the Earth the Celestial Ephemeris Pole CEP or celestial pole does not stay still on the surface of the Earth The Celestial Ephemeris Pole is calculated from observation data and is averaged so it differs from the instantaneous rotation axis by quasi diurnal terms which are as small as under 0 01 see 6 In setting up a coordinate system a static terrestrial point called the IERS Reference Pole or IRP is used as the origin the x axis is in the direction of IRM the IERS Reference Meridian the y axis is in the direction 90 degrees West longitude x and y are the coordinates of the CEP relative to the IRP Pole coordinates can be determined using various space geodesy and satellite geodesy techniques e g Satellite laser ranging Very Long Baseline Interferometry however the most accurate techniques are GPS GLONASS and Galileo 7 Celestial pole offsets edit Celestial pole offsets are described in the IAU Precession and Nutation models The observed differences with respect to the conventional celestial pole position defined by the models are monitored and reported by the IERS Celestial pole offsets can only be obtained by the VLBI The observed CPO can quantify the deficiencies of the IAU2006 2000A precession nutation model including the astronomically forced nutations and a component of nutation that is considered unpredictable Some studies indicate that substantial FCN Free Core Nutation amplitude and phase disturbances occurred at the epochs close to the revealed GMJ Geomagnetic Jerk events 8 9 References edit Dobslaw Henryk Dill Robert February 2018 Predicting Earth orientation changes from global forecasts of atmosphere hydrosphere dynamics Advances in Space Research 61 4 1047 1054 Bibcode 2018AdSpR 61 1047D doi 10 1016 j asr 2017 11 044 Zajdel Radoslaw Sosnica Krzysztof Bury Grzegorz Dach Rolf Prange Lars July 2020 System specific systematic errors in earth rotation parameters derived from GPS GLONASS and Galileo GPS Solutions 24 3 74 doi 10 1007 s10291 020 00989 w Zajdel R Sosnica K Drozdzewski M Bury G Strugarek D November 2019 Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS Journal of Geodesy 93 11 2293 2313 Bibcode 2019JGeod 93 2293Z doi 10 1007 s00190 019 01307 0 Sosnica K Bury G Zajdel R 16 March 2018 Contribution of Multi GNSS Constellation to SLR Derived Terrestrial Reference Frame Geophysical Research Letters 45 5 2339 2348 Bibcode 2018GeoRL 45 2339S doi 10 1002 2017GL076850 S2CID 134160047 Modiri S Belda S Hoseini M Heinkelmann R Ferrandiz Jose M Schuh H February 2020 A new hybrid method to improve the ultra short term prediction of LOD Journal of Geodesy 94 23 23 Bibcode 2020JGeod 94 23M doi 10 1007 s00190 020 01354 y PMC 7004433 PMID 32109976 Seidelmann P K 1982 Celest Mech 27 79 Zajdel Radoslaw Sosnica Krzysztof Bury Grzegorz Dach Rolf Prange Lars Kazmierski Kamil January 2021 Sub daily polar motion from GPS GLONASS and Galileo Journal of Geodesy 95 1 3 Bibcode 2021JGeod 95 3Z doi 10 1007 s00190 020 01453 w Modiri Sadegh Heinkelmann Robert Belda Santiago Malkin Zinovy Hoseini Mostafa Korte Monika Ferrandiz Jose M Schuh Harald November 2021 Towards Understanding the Interconnection between Celestial Pole Motion and Earth s Magnetic Field Using Space Geodetic Techniques Sensors 21 22 7555 Bibcode 2021Senso 21 7555M doi 10 3390 s21227555 PMC 8621431 PMID 34833631 Malkin Zinovy Belda Santiago Modiri Sadegh August 2022 Detection of a New Large Free Core Nutation Phase Jump Sensors 22 16 5960 Bibcode 2022Senso 22 5960M doi 10 3390 s22165960 PMC 9414530 PMID 36015720 External links edithttp hpiers obspm fr eop pc http www usno navy mil USNO earth orientation https web archive org web 20130802032453 http maia usno navy mil http www iers org Retrieved from https en wikipedia org w index php title Earth orientation parameters amp oldid 1188067758, wikipedia, wiki, book, books, library,
