ACE Hourly Data Parameters for Magnetospheric Driving

This is a high-level data product deamed useful by some for studies of magnetospheric disturbances and solar wind turbulence. We are happy to provide it as a biproduct of our own research efforts, but we recommend that the user approach with care. This is NOT part of the standard ACE data routinely made available to the public as Level-2 products.

Overview:

The data files provided here were created to assess magnetospheric disturbance drivers and their responses. However, they are also useful in performing analyses of interplanetary turbulence. The data files are evolving and we welcome comments and suggestions from interested potential users of the data product. In the interest of openness and with the hope of providing the best data product possible, we are also providing the source program for your examination.

We provide two data files with identical data formatting. Each computes a number of statistical quantities for the interplanetary magnetic field, wind velocity, density, and temperature over a one-hour period. See MAG Instrument and SWEPAM Instrument for complete descriptions of the instruments.

Both data files are based on hourly intervals of ACE data. The data clock is NOT set to the start of the hour in UT time, but is a simple 60-min average of the ACE 64-s data products. Both files contain means, 2nd-order, and 4th-order moments of the distributions internal to each 60-min interval along with two-parameter fits (amplitude and index) to 2nd-order structure functions.

The two files are distinguished by the use of detrending within the hourly interval used on some variables in the detrend data file.

Anyone using these data are invited to contact C.W. Smith at Charles.Smith@unh.edu with any questions they may have.

Data Types:

Each hour of data contains several types of high-level data products. Data is first obtained by us in RTN coordinates most suitable for interplanetary studies as these define the coordinate system of the Parker spiral. Data has 64-second resolution.

• Simple means and variances of data and products are computed based on one-hour subsets of the data.
• The data is rotated into mean magnetic field coordinates as defined and used by Belcher and Davis (1971) and Bieber et al. (1996):
  x direction given by unit vector in B0 x (B0 x R)
  y direction given by unit vector in -B0 x R
  z direction given by mean field direction B0
• Simple means and variances are again computed in rotated coord. system.
• Second order structure functions are computed in both coordinate systems.
• Maximum lags of 10 points = 640 sec are used.
• Resulting structure functions are fit with amplitudes, indices, and uncertainties.
• This is performed in both RTN and x,y,z coordinate systems.
• We recommend against using density and temperature fits at this time as there is evidence of poor functional fits using powerlaws.

Data Format:

The table below provides a listing of variables and their description. Each is based on a 1-hour data subset (57 points or fewer at 64-s resolution omitting badpoints) and no quantities are summed or in any way manipulated on larger time scales.

Variable	Definition
iy1	Year at start of 1-hour interval
t1	Digital day at start of 1-hour interval
Vsw	Average wind speed over 1-hour interval
Vsw2	Average square of wind speed over 1-hour interval
Vr_mean	Average R-component of wind speed over 1-hour interval
Vr_mean2	Average square of R-component of wind speed over 1-hour interval
Vt_mean	Average T-component of wind speed over 1-hour interval
Vt_mean2	Average square of T-component of wind speed over 1-hour interval
Vn_mean	Average N-component of wind speed over 1-hour interval
Vn_mean2	Average square of N-component of wind speed over 1-hour interval
Va_mean	Average Alfven speed over 1-hour interval
Va_mean2	Average square of Alfven speed over 1-hour interval
pTemp	Average proton temperature over 1-hour interval
pTemp2	Average square of proton temperature over 1-hour interval
pDen	Average number density of protons over 1-hour interval
pDen2	Average square of number density of protons over 1-hour interval
beta	Average plasma beta for protons over 1-hour interval
beta2	Average square of plasma beta for protons over 1-hour interval
zlambda_ii	Average proton ion inertial scale over 1-hour interval
zlambda_ii2	Average square of proton ion inertial scale over 1-hour interval
B	Average IMF intensity over 1-hour interval
B2	Average square of IMF intensity over 1-hour interval
Brms_mean	Average rms fluctuation of IMF over 1-hour interval summed over components
Brms_mean2	Average square of rms fluctuations of IMF over 1-hour interval summed over components
Br_mean	Average R-component of IMF over 1-hour interval
Br_mean2	Average square of R-component of IMF over 1-hour interval
Bt_mean	Average T-component of IMF over 1-hour interval
Bt_mean2	Average square of T-component of IMF over 1-hour interval
Bn_mean	Average N-component of IMF over 1-hour interval
Bn_mean2	Average square of N-component of IMF over 1-hour interval
Bvar
sigma_Bvar
B_squared	Average square of IMF intensity over 1-hour interval
B2_squared	Average square of IMF intensity variance over 1-hour interval
Br_mean_squared	Average square of IMF R-component over 1-hour interval
Br_mean2_squared	Average square of IMF R-component variance over 1-hour interval
Bt_mean_squared	Average square of IMF T-component over 1-hour interval
Bt_mean2_squared	Average square of IMF T-component variance over 1-hour interval
Bn_mean_squared	Average square of IMF N-component over 1-hour interval
Bn_mean2_squared	Average square of IMF N-component variance over 1-hour interval
Vsw_squared	Average square of solar wind speed over 1-hour interval
Vsw2_squared	Average square of solar wind speed variance over 1-hour interval
Vr_mean_squared	Average square of solar wind velocity R-component over 1-hour interval
Vr_mean2_squared	Average square of solar wind velocity R-component variance over 1-hour interval
Vt_mean_squared	Average square of solar wind velocity T-component over 1-hour interval
Vt_mean2_squared	Average square of solar wind velocity T-component variance over 1-hour interval
Vn_mean_squared	Average square of solar wind velocity N-component over 1-hour interval
Vn_mean2_squared	Average square of solar wind velocity N-component variance over 1-hour interval
Vvar
sigma_Vvar
VdotB_aver	Average value of V,B fluctuations inner product
VdotB_aver_var	Standard deviation of V,B fluctuations inner product
VdotB_inst
VdotB_inst_var
Baniso	Mean square fluctuation of IMF perpendicular to mean magnetic field over parallel
Vaniso	Mean square fluctuation of velocity perpendicular to mean magnetic field over parallel
Structure Functions:	Results derived from 2nd order structure function fits:
Btrace_A	Fit amplitude for trace IMF 2nd order structure function
Btrace_B	Fit index for trace IMF 2nd order structure functions
Btrace_sigmaA	Uncertainty to fit amplitude for trace IMF 2nd order structure function
Btrace_sigmaB	Uncertainty to fit index for trace IMF 2nd order structure functions
Vtrace_A	Fit amplitude for trace velocity 2nd order structure function
Vtrace_B	Fit index for trace velocity 2nd order structure functions
Vtrace_sigmaA	Uncertainty to fit amplitude for trace velocity 2nd order structure function
Vtrace_sigmaB	Uncertainty to fit index for trace velocity 2nd order structure functions
Tp_A	Fit amplitude for temperature 2nd order structure function
Tp_sigmaA	Uncertainty to fit amplitude for temperature 2nd order structure function
Tp_B	Fit index for temperature 2nd order structure function
Tp_sigmaB	Uncertainty to fit index for temperature 2nd order structure function
Np_A	Fit amplitude for density 2nd order structure function
Np_sigmaA	Uncertainty to fit amplitude for density 2nd order structure function
Np_B	Fit index for denisty 2nd order structure function
Np_sigmaB	Uncertainty to fit index for density 2nd order structure function
Bx_A	Fit amplitude for IMF x-component 2nd order structure function
Bx_sigmaA	Uncertainty to fit amplitude for IMF x-component 2nd order structure function
Bx_B	Fit index for IMF x-component 2nd order structure functions
Bx_sigmaB	Uncertainty to fit index for IMF x-component 2nd order structure functions
By_A	Fit amplitude for IMF y-component 2nd order structure function
By_sigmaA	Uncertainty to fit amplitude for IMF y-component 2nd order structure function
By_B	Fit index for IMF y-component 2nd order structure functions
By_sigmaB	Uncertainty to fit index for IMF y-component 2nd order structure functions
Bz_A	Fit amplitude for IMF z-component 2nd order structure function
Bz_sigmaA	Uncertainty to fit amplitude for IMF z-component 2nd order structure function
Bz_B	Fit index for IMF z-component 2nd order structure functions
Bz_sigmaB	Uncertainty to fit index for IMF z-component 2nd order structure functions
Vx_A	Fit amplitude for velocity x-component 2nd order structure function
Vx_sigmaA	Uncertainty to fit amplitude for velociyt x-component 2nd order structure function
Vx_B	Fit index for velocity x-component 2nd order structure functions
Vx_sigmaB	Uncertainty to fit index for velocity x-component 2nd order structure functions
Vy_A	Fit amplitude for velocity y-component 2nd order structure function
Vy_sigmaA	Uncertainty to fit amplitude for velocity y-component 2nd order structure function
Vy_B	Fit index for velocity y-component 2nd order structure functions
Vy_sigmaB	Uncertainty to fit index for velocity y-component 2nd order structure functions
Vz_A	Fit amplitude for velocity z-component 2nd order structure function
Vz_sigmaA	Uncertainty to fit amplitude for velocity z-component 2nd order structure function
Vz_B	Fit index for velocity z-component 2nd order structure functions
Vz_sigmaB	Uncertainty to fit index for velocity z-component 2nd order structure functions
Bx_A_rtn	Fit amplitude for IMF R-component 2nd order structure function
Bx_sigmaA_rtn	Uncertainty to fit amplitude for IMF R-component 2nd order structure function
Bx_B_rtn	Fit index for IMF R-component 2nd order structure functions
Bx_sigmaB_rtn	Uncertainty to fit index for IMF R-component 2nd order structure functions
By_A_rtn	Fit amplitude for IMF T-component 2nd order structure function
By_sigmaA_rtn	Uncertainty to fit amplitude for IMF T-component 2nd order structure function
By_B_rtn	Fit index for IMF T-component 2nd order structure functions
By_sigmaB_rtn	Uncertainty to fit index for IMF T-component 2nd order structure functions
Bz_A_rtn	Fit amplitude for IMF N-component 2nd order structure function
Bz_sigmaA_rtn	Uncertainty to fit amplitude for IMF N-component 2nd order structure function
Bz_B_rtn	Fit index for IMF N-component 2nd order structure functions
Bz_sigmaB_rtn	Uncertainty to fit index for IMF N-component 2nd order structure functions
Vx_A_rtn	Fit amplitude for velocity R-component 2nd order structure function
Vx_sigmaA_rtn	Uncertainty to fit amplitude for velociyt R-component 2nd order structure function
Vx_B_rtn	Fit index for velocity R-component 2nd order structure functions
Vx_sigmaB_rtn	Uncertainty to fit index for velocity R-component 2nd order structure functions
Vy_A_rtn	Fit amplitude for velocity T-component 2nd order structure function
Vy_sigmaA_rtn	Uncertainty to fit amplitude for velocity T-component 2nd order structure function
Vy_B_rtn	Fit index for velocity T-component 2nd order structure functions
Vy_sigmaB_rtn	Uncertainty to fit index for velocity T-component 2nd order structure functions
Vz_A_rtn	Fit amplitude for velocity N-component 2nd order structure function
Vz_sigmaA_rtn	Uncertainty to fit amplitude for velocity N-component 2nd order structure function
Vz_B_rtn	Fit index for velocity N-component 2nd order structure functions
Vz_sigmaB_rtn	Uncertainty to fit index for velocity N-component 2nd order structure functions
Vx_mean	Average of solar wind velocity in mean magnetic field x-component direction
Vx_mean2	Variance of solar wind velocity in mean magnetic field x-component direction
Bx_mean	Average of IMF in x-component
Bx_mean2	Variance of IMF in x-component
Vy_mean	Average of solar wind velocity in mean magnetic field y-component direction
Vy_mean2	Variance of solar wind velocity in mean magnetic field y-component direction
By_mean	Average of IMF in y-component
By_mean2	Variance of IMF in y-component
Vz_mean	Average of solar wind velocity in mean magnetic field z-component direction
Vz_mean2	Variance of solar wind velocity in mean magnetic field z-component direction
Bz_mean	Average of IMF in z-component
Bz_mean2	Variance of IMF in z-component
Vx_mean2	Kurtosis of solar wind velocity in mean magnetic field x-component direction
Vy_mean2	Kurtosis of solar wind velocity in mean magnetic field y-component direction
Vz_mean2	Kurtosis of solar wind velocity in mean magnetic field z-component direction
Bx_mean2	Kurtosis of IMF x-component
By_mean2	Kurtosis of IMF y-component
Bz_mean2	Kurtosis of IMF z-component

Data Files, Souce and Analysis Codes:

We provide the data in two forms:

In the first form the data is computed directly as described above with no additional manipulation. That data file is: THA.out available in ascii (181KBytes). It is the full data file, not broken up by year or in any other manner.

The second data file has the added benefit that variances and structure functions are computed after a third-order detrend of the hourly subset. This yields a truer evaluation of the variance and spectra for the turbulent fluctuations by removing the large-scale trends, but may be less useful in describing the fluctuations that impact the magnetopause. That data file is: THA_detrend.out available in ascii (181KBytes). It is again the full data file, not broken up by year or in any other manner.

We provide two codes used in the production and analysis of the data files made available here. Both are written in low-level, transportable Linux Fortran.

The source fortran code used to generate the above variables is turb_parms.for available in ascii (59MBytes).

The fortran code to read the above variables is read_tha_output_demo.for available in ascii (15KBytes). Note that this code will only read the output file and does not calculations. Those are for you to develop.

Other Useful and Relevant ACE Links:

The following links are useful in learning more about the ACE dataset:

• ACE Home Page.
• ACE Science Center - The central source for all ACE investigations, including pointers to instrument pages and data sources.
• ACE/MAG Home Page - Details on the Magnetic Field Instrument.
• ACE/SWEPAM Homepage - Details on the Solar Wind Electron Proton Alpha Monitor.
• ACE News - A biweekly report of developing ACE science results.