Atmospheric Pressure Loading Service


Contents:

Abstract

This page provides links to files relevant to the service of the atmospheric pressure loading provided by the VLBI group at NASA Goddard Space Flight Center. The service provides time series of 3-D displacement for many space geodesy stations and updates them every night. The data products on this site are IERS Global Geophysical Fluids Center Provisional Products.

Change log and plans.

Introduction

The Earth as a whole responses to external forces as an elastic body. As it was shown by Darwin in 1882, changes of the weight of the column of atmosphere due to variations of pressure result in crustal deformations called atmospheric pressure loading. These variations on average have the rms of 2.6 mm for the vertical component and 0.6 mm for the horizontal component, but peak to peak variations can reach 40 mm for the vertical component and 7 mm for the horizontal one. Pressure loading should be taken into account in a reduction of astronomical and space geodesy observations when the accuracy better than 2 nrad or 1 cm is required.

Service for the atmospheric pressure loading

On 2002.12.12 the service of atmospheric pressure loading was established.

The series of the 3-D displacements with respect to the center of mass of the total Earth, the solid Earth and atmosphere, due to pressure loading with a 6 hour time resolution are computed for 824 sites at VLBI, SLR, GPS and DORIS, stations. The first epoch of the time series for each station is 3 days before any station at the site started operation. The last epoch of the time series is 3 days after the station ceased operation, or the last date when the atmospheric pressure field is available if the station is still active. Site identifier for a VLBI site is the IVS name, for SLR site is a 8-letter long station name, for GPS and DORIS sites is a 4-letter long station name. If more than one station of any technique is located within the distance of 3000 meters, then the pressure loading is provided for only one station of the site. The tables of the correspondence between VLBI station names and site identifiers as well as SLR station names, GPS station names and DORIS station names are provided.

In addition to that, the time series of 3D displacements with 6 hour time resolution are computed on the 2.5x2.5 deg grid.

Files for downloading

  1. These series are updated daily. The update process starts at 04:00 local time.
    The files were updated last time on       2014.04.23-06:45:59 (UTC) 
    Atmospheric pressure loading last epoch:  2014.04.20-18:00:00 (UTC) 
    
    

    File Format Size Comment
    aplo_2m_eph.tar.bz2 EPHEDISP
    Data are archived with tar and bzip2.
    1 Mb This compressed tar-file contains a directory of ascii files of atmospheric pressure loading from 00:00 of the first day of the previous month through 2012.01.21-18:00:00
    aplo_ty_eph.tar.bz2 EPHEDISP
    Data are archived with tar and bzip2.
    6 Mb This compressed tar-file contains a directory of ascii files of atmospheric pressure loading for 683 sites from 01-JAN 00:00 this year through 2012.01.21-18:00:00
    aplo_py_eph.tar.bz2 EPHEDISP
    Data are archived with tar and bzip2.
    250 Mb This compressed tar-file contains a directory of ascii files of atmospheric pressure loading for 683 sites from 1976.01.01 till 31-DEC 18:00 of the previous year.
    aplo_bds.tar.bz2 BINDISP
    Data are archived with tar and bzip2.
    165 Mb This compressed tar-file contains a directory of binary files of atmospheric pressure loading for 683 sites in the form suitable for reduction of observations. The plug-in interface to the Mark-5 VLBI analysis programs, VTD, Calc/Solve and GEODYN is provided.
    aplo_eph EPHEDISP
    3063 Mb This is the link to the directory with uncompressed ascii files of atmospheric pressure loading for 683 sites from 1976.01.01_00:00 through 2012.01.21-18:00:00
    aplo_geonet_bds.tar.bz2 BINDISP
    Data are archived with tar and bzip2.
    94 Mb This compressed tar-file contains a directory of binary files of atmospheric pressure loading for 1224 GEONET sites in the form suitable for reduction of observations. The plug-in interface to the Mark-5 VLBI analysis programs VTD, Calc/Solve and GEODYN is provided. These files currently are NOT BEING UPDATED.
    aplo_geonet_eph.tar.bz2 EPHEDISP
    Data are archived with tar and bzip2.
    117 Mb This compressed tar-file contains a directory of ascii files of atmospheric pressure loading for 1224 GEONET sites from 1992.01.01_00:00 through 2005.10.14_18:00. These files currently are NOT BEING UPDATED.
    aplo_geonet_eph EPHEDISP
    1930 Mb This is the link to the directory with uncompressed ascii files of atmospheric pressure loading for 1224 GEONET sites from 1992.01.01_00:00 through 2005.10.14_18:00. These files currently are NOT BEING UPDATED.
    aplo_py_nc.tar.bz2 netCDF
    Data are archived with tar and bzip2.
    1622 Mb This compressed tar-file contains a directory of binary files of atmospheric pressure loading on the 2.5x2.5 deg grid from 1976.01.01_00:00:00 file first day of the previous month through till 31-DEC 18:00 of the previous year.
    aplo_ty_nc.tar.bz2 netCDF
    Data are archived with tar and bzip2.
    30 Mb This compressed tar-file contains a directory of binary files of atmospheric pressure loading on the 2.5x2.5 deg grid from 01-JAN 00:00 this year through 2012.01.21-18:00:00
    aplo_2m_nc.tar.bz2 netCDF
    Data are archived with tar and bzip2.
    5 Mb This compressed tar-file contains a directory of binary files of atmospheric pressure loading on the 2.5x2.5 deg grid from 00:00 of the first day of the previous month through 2012.01.21-18:00:00
    aplo_grid_eph EPHEDISP
    36 Gb This is the link to the directory with uncompressed ascii files of atmospheric pressure loading on the 2.5x2.5 deg grid from 1976.01.01 through 2012.01.21-18:00:00
    aplo_grid_nc netCDF
    2819 Mb This is the link to the directory with uncompressed ascii files of atmospheric pressure loading on the 2.5x2.5 deg grid from 1976.01.01 through 2012.01.21-18:00:00

    NB: All these files have the same data in different formats.

  2. The list of coefficients of harmonic site position variations with respect to the center of mass of the total Earth, the solid Earth and the atmosphere, caused by the atmospheric variations at diurnal at semidiurnal frequencies in the HARPOS format. The coefficients are computed on the basis of the Ponte and Ray (2002) model. The plug-in interface to the Mark-5 VLBI analysis software VTD, Calc/Solve and GEODYN is provided.
  3. Two sets of coefficients are available:

  4. Coefficients of harmonic 3D displacements caused by the S1 and S2 variations of the atmospheric pressure on the 1x1 deg grid in the NetCDF format. The coefficients are computed on the basis of the Ponte and Ray (2002) model. Two sets of coefficients are available:

The time series have zero mean and no signal at S1 and S2 frequencies. The total displacement is the sum of the time series and the model of harmonic site position variations caused by atmospheric tides at the S1 and S2 frequencies.

Other related files

  1. Movie of the Up component of displacements caused by the atmospheric pressure loading (35Mb).
  2. Movie of the East component of displacements caused by the atmospheric pressure loading (35Mb).
  3. Movie of the North component of displacements caused by the atmospheric pressure loading (35Mb).
  4. Source code of the programs for computing the atmospheric pressure loading.
  5. Gridded values of the mean surface pressure in NetCDF format.
  6. Gridded values of the S1 and S2 variations of atmospheric pressure in NetCDF format which are present in raw NCEP Reanalysis pressure field. This model of atmospheric tide has been subtracted from the raw NCEP Reanalysis surface pressure field before computing loading.
  7. Gridded values of the S1 and S2 variations of atmospheric pressure in NetCDF format according to the Ponte and Ray (2002) model at 1ox1o grid, and the same model on the 2.5ox2.5o grid.
  8. Plots of S1 and S2 variations of atmospheric pressure according to the Ponte and Ray (2002) model at 1ox1o grid:

    Cos Sin Amp Phs
    S1 S1 S1 S1
    S2 S2 S2 S2
  9. Gridded values of the 2.5ox2.5o land-sea mask in NetCDF format.
  10. Gridded values of the 0.25ox0.25o land-sea mask in NetCDF format.
  11. CM Green's function in the coordinate system with the center of mass of the total Earth: solid Earth and the mass which causes the loading. The first column is the angular separation between a station and the mass load in degrees, the second column is radial Green's function, the third column is the horizontal Green's function.
  12. CE Green's function in the coordinate system with the center of mass of the solid Earth. The first column is the angular separation between a station and the mass load in degrees, the second column is radial Green's function, the third column is the horizontal Green's function.
  13. Load Love numbers of the the second order in the coordinate system with the center of mass of the total Earth. The first column is the load Love number h, the second column is the load Love number l, the third columns is the load Love number k.
  14. Plots of displacements caused by the loading caused by the diurnal (S1) and semi-diurnal (S2) variations in the atmospheric pressure on the 1ox1o grid:
  15. List of VLBI, SLR, GPS and DORIS sites. Several VLBI and/or SLR and/or GPS and/or stations were combined in one site if the distance between them does not exceed 3000 meters. This is a control file which was used for computation of these series.
  16. List of VLBI station names and site identifiers and the list of their coordinates.
  17. List of SLR station names and the list of their coordinates.
  18. List of GPS station names and site identifiers and the list of their coordinates.
  19. List of DORIS station names and site identifiers and the list of their coordinates.
  20. Brief log file of the service. Time tag in local time.
  21. Verbose raw log file of the service. Time tag in local time.
  22. History of updates of the atmospheric pressure loading series. Time tag in UTC. The first column is the date of the update, the second column is the date of the last epoch of the atmospheric pressure loading time series.

Smart downloading

Time series are updated every day automatically. It is assumed that regular users also use automatic routines for retrieval the series. Some tips: the date of the latest epoch of the time series is stored in http://lacerta.gsfc.nasa.gov/aplo/loading_date.txt. Examining the date stored in this file, the client process can determine whether the time series have been updated. Package wget is suitable for data retrieval. An example of the client program which is scheduled by cron every hour can be found here.

Latency

Atmospheric pressure loading is computed within 24 hours after availability of the surface atmospheric pressure field of the NCEP Reanalysis model. NCEP Reanalysis model lags about 3 days. At 90% cases the atmospheric pressure loading time series has lag 2.6 days. At 10% cases the lag is in the range of 4-15 days. The plot of latency for last 2 months is available here.

Method

For computing site displacements caused by atmospheric pressure loading at a given point a global distribution of atmospheric surface pressure and the response of the ocean surface driven by atmosphere forcing should be known. We computed atmospheric pressure loading by convolving Farrell Green's function derived on the basis of the preliminary Earth model (PREM) with of the surface pressure field with 2.5ox2.5o resolution with 6 hour time resolution provided by NCEP/NCAR Reanalysis numerical whether model after subtraction the mean surface pressure and the model of diurnal and semi-diurnal variations of surface pressure computed from the NCEP reanalysis surface pressure field over the period of 1980-2002. The displacements are computed with respect to the center of mass of the total Earth: solid Earth and atmosphere. The oceanic response was modeled according to the inverted barometer hypothesis (the variant with conservation of the total ocean water mass). The FES99 land-sea mask with resolution of 0.25ox0.25o was used. This model of atmospheric pressure loading was extensively tested against VLBI data, and it was adopted in January 2003 for using in processing VLBI data for Goddard quarterly and operational VLBI solutions. Results of these study were summarized in the paper:

L. Petrov, J.-P. Boy, Study of the atmospheric pressure loading signal in VLBI observations, Journal of Geophysical Research, 10.1029/2003JB002500, Vol. 109, No. B03405, 2004.
|  Abstract   |   Full text in PostScript+gzip (356Kb)   |   Full text in PDF (871Kb)   |

Citation instruction

If you use this time series in your analysis, you are welcome to acknowledge in your publication that you used "atmospheric pressure loading time series provided by the Goddard VLBI group which are available on the Web at http://gemini.gsfc.nasa.gov/aplo (Petrov & Boy, 2004)" and include the following reference in the bibliography list:

L. Petrov, J.-P. Boy, Study of the atmospheric pressure loading signal in VLBI observations, Journal of Geophysical Research, 10.1029/2003JB002500, Vol. 109, No. B03405, 2004.

Similar services

  1. Service of the atmospheric contribution to geopotential into a series of spherical harmonics up to degree/order 72/72 and 20/20 which are updated every night.
  2. Professor Hans-Georg Scherneck provides an alternative dataset of the atmospheric pressure loading displacements for many VLBI, SLR and GPS sites at his Web site.
  3. Regression coefficients between the local atmospheric pressure and the vertical displacements due to atmospheric pressure loading at the International Earth Rotation Service Special Bureau for Loading are available at their web site and briefly explained here.
  4. Pascal Gegout and computed time series of pressure loading signals for ITRF sites which are available here.
  5. Tonie van Dam computed time series of pressure loading signals for ITRF sites which are available here.
  6. Dr. Kierulf computed time series of pressure loading signals for ITRF sites which are available here.

References

  1. Darwin, G.H., On variations in the vertical due to elasticity of the Earth's surface, Phil. Mag., Ser. 5, col. 14, N. 90, 409--427, 1882.
  2. Farrell, W.E, Deformation of the Earth by Surface Loads, Rev. Geophys. and Spac. Phys., vol. 10(3), pp. 751--797, 1972.
  3. Kalnay E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J. Woollen, Y. Zhu, A. Leetma, R. Reynolds, M. Chelliah, W. Ebisuzaki, W.Higgins, J. Janowiak, K. C. Mo, C. Ropelewski, J. Wang, R. Jenne and D. Joseph, The NCEP/NCAR 40-Year Reanalysis Project, Bullet. Amer. Meteorol. Soc., vol. 77, pp. 437--471, 1996.
  4. Lefevre, F., F.H. Lyard, C. Le Provost and E.J.O. Schrama, FES99: a global tide finite element solution assimilating tide gauge and altimetric information, J. Atmos. Oceanic Technol., vol. 19, pp.1345--1356, 2002.
  5. Manabe, S., T. Sato, S. Sakai, K. Yokoyama, Atmospheric load effect on VLBI observations, Proc. of the AGU Chapman conference on geodetic VLBI: Monitoring global change, NOAA TR NOS 437, NGS 49, Washington D.C., pp.111--122, 1991.
  6. MacMillan, D.S. and J.M. Gipson, Atmospheric pressure loading parameters from very long baseline interferometric observations, J. Geophys. Res., vol. 99(B9), pp. 18,081--18,087, 1994.
  7. Ponte, R.M. and Ray, R.D., Atmospheric pressure correction in geodesy and oceanography: A strategy for handling air tides, Geophys. Res. Let., vol. 29, (24), 2153, doi:10.1029/2002GL016340, 2002.
  8. van Dam, T.M. and T.A. Herring, Detection of atmospheric pressure loading using Very Long Baseline Interferometry measurements, J. Geophys. Res. 99(B3), pp. 4505--4518, 1994.
  9. van Dam, T.M., G. Blewitt, and M. Heflin, Detection of atmospheric pressure loading using the Global Positioning System, J. Geophys. Res., vol. 99(B12), pp. 23,939--23,950, 1994.
  10. van Dam, T.M. and J. Wahr, Displacements of the Earth's surface due to atmospheric loading: Effects on gravity and baseline measurements, J. Geophys. Res., vol. 92, pp. 1281--1286, 1987.
  11. Wunsch, C. and D. Stammer, Atmospheric loading and the "inverted barometer" effect, Rev. Geophys., vol. 35, pp. 117--135, 1997.

Mailing list

Mailing list list_loading@gemini.gsfc.nasa.gov is for discussing issues related to the atmospheric pressure loading service and for posting messages about changes. Only subscribers can post messages to the list. The messages posted to the list are available for viewing to all from the mail archive.

In order to subscribe or un-subscribe, please fill a registration form.


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This page was prepared by Leonid Petrov ()
Last update: 2012.07.17_12:46:21