Variable Examples¶
Data Variables¶
Example of Scalar Density Variable¶
The example demonstrates a scalar data variable SW_P_Den displayed in CDAWeb as a time series (DISPLAY_TYPE = "time_series") and its corresponding definition as it appears in a CDF Skeleton table. All required and some recommended variable attributes are included. On the corresponding plot, the y-axis labels come from the variable attributes LABLAXIS and UNITS. The x-axis is defined by the support_data variable Epoch (time, see examples here) attached via SW_P_Den variable’s DEPEND_0 attribute. Since SW_P_Den is a 0-dimensional variable, it does not require any other DEPEND_i attributes.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"SW_P_Den" CDF_REAL4 1 0 T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "data" }.
"FIELDNAM" CDF_CHAR { "Ion Number Density (CPI/SWA)" }
"CATDESC" CDF_CHAR { "Ion number density (Solar Wind " -
"Analyzer), scalar" }
"DEPEND_0" CDF_CHAR { "Epoch" }
"LABLAXIS" CDF_CHAR { "Ion N" }
"UNITS" CDF_CHAR { "#/cc" }
"FORMAT" CDF_CHAR { "F8.3" }
"VALIDMIN" CDF_REAL4 { 0.01 }
"VALIDMAX" CDF_REAL4 { 1000.0 }
"FILLVAL" CDF_REAL4 { -1.0e+31 }
"DISPLAY_TYPE" CDF_CHAR { "time_series" }
"DICT_KEY" CDF_CHAR { “SPASE>Particle>ParticleType:Ion," -
"ParticleQuantity:NumberDensity” }
"VAR_NOTES" CDF_CHAR { "Assuming no helium (0.3 - several " -
"hundred) if the density is less than " -
"0.3/cc the higher moments (VEL,TEMP) " -
"shall not be used because of the poor " -
"counting statistics." }
Example of Vector Magnetic Field Variable¶
Data variable BGSE (Vector Magnetic Field) is displayed as time series plots (DISPLAY_TYPE = "time_series"), one for each vector component. The vector variable does not need DEPEND_1 attribute since it does not depend on any additional numerical data. The x-axis is defined by the support_data variable Epoch (time) attached via BGSE variable’s DEPEND_0 attribute. The y-axis labels come from two places: (1) ["Bx GSE", "By GSE", "Bz GSE"] array of strings (labeled in blue) from the metadata variable label_B_GSE (described here) which is attached to BGSE via the LABL_PTR_1 attribute and (2) "nT" from the UNITS attribute. Note that if each vector component requires distinct unit or format string, instead of using UNITS and FORMAT attributes, the string arrays must be provided in separate metadata variables attached to the data variable via UNIT_PTR and FORM_PTR attributes.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"BGSE" CDF_REAL4 1 1 3 T T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "data" }.
"FIELDNAM" CDF_CHAR { "B field in GSE coordinates (1 min)" }
"CATDESC" CDF_CHAR { "Magnetic field vector in GSE" -
"cartesian coordinates (1 min)" }
"DEPEND_0" CDF_CHAR { "Epoch" }
"LABL_PTR_1" CDF_CHAR { "label_B_GSE" }
"UNITS" CDF_CHAR { "nT" }
"FORMAT" CDF_CHAR { "E13.6" }
"VALIDMIN" CDF_REAL4 { -65534.0 }
"VALIDMAX" CDF_REAL4 { 65534.0 }
"FILLVAL" CDF_REAL4 { -1.0e+31 }
"SCALETYP" CDF_CHAR { "linear" }
"DISPLAY_TYPE" CDF_CHAR { "time_series" }
"DICT_KEY" CDF_CHAR { “SPASE>Field>FieldQuantity:Magnetic," -
"Qualifier:Vector,CoordinateSystemName:GSM," -
"CoordinateRepresentation:Cartesian” }
Example of 1-D Flux Variable¶
A 1-D data variable IDiffI_I (Ion Diff. Intensity at 12 energies) is displayed as a spectrogram (DISPLAY_TYPE = "spectrogram"). The z-axis labels come from variable attributes LABLAXIS and UNITS. The y-axis labels (labeled in green) come from the energy variable IDiffI_I_Energy (support_data, described here) attached to IDiffI_I via the DEPEND_1 attribute, specifically the LABLAXIS (or FIELDNAM) and UNITS of the energy variable. The x-axis is defined by the support_data variable Epoch (time) attached via DEPEND_0 attribute.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"IDiffI_I" CDF_REAL4 1 1 12 T T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "data" }
"FIELDNAM" CDF_CHAR { "Spin-avg Ion Diff Inten (EPIC/ICS)" }
"CATDESC" CDF_CHAR { "Ion Diff. Intensity, at 12 energies " -
"67-1361 keV (EPIC/ICS)" }
"DEPEND_0" CDF_CHAR { "Epoch" }
"DEPEND_1" CDF_CHAR { "IDiffI_I_Energy" }
"LABLAXIS" CDF_CHAR { "dJ/dE" }
"UNITS" CDF_CHAR { "1/[cm**2-s-sr-keV]" }
"FORMAT" CDF_CHAR { "E9.3" }
"VALIDMIN" CDF_REAL4 { 1.000000e-04 }
"VALIDMAX" CDF_REAL4 { 1.000000e+10 }
"FILLVAL" CDF_REAL4 { -1.000000e+31 }
"DELTA_PLUS_VAR" CDF_CHAR { "IDiffI_I_Uncert" }
"DELTA_MINUS_VAR" CDF_CHAR { "IDiffI_I_Uncert" }
"SCALETYP" CDF_CHAR { "log" }
"DISPLAY_TYPE" CDF_CHAR { "spectrogram" } .
"DICT_KEY" CDF_CHAR { "SPASE>Particle>ParticleType:Ion," -
"ParticleQuantity:NumberFlux," -
"Qualifier:Differential_Vector" }
As an alternative to spectrogram, stack plot (DISPLAY_TYPE = "stack_plot") also displays all 1-D data on a single plot. The following plot shows an Electron Flux variable at 7 energies displayed as a stack plot. As opposed to spectrogram, the y-axis labels come from variable attributes LABLAXIS and UNITS. The z-axis labels (labeled in green) come from the energy variable attached to the Electron Flux variable via the DEPEND_1 attribute, specifically the LABLAXIS (or FIELDNAM) and UNITS of the energy variable. The x-axis is defined by the support_data variable Epoch (time) attached via DEPEND_0 attribute.
Example of 2-D Flux Variable¶
The following 2-D (sizes 28,12) data variable Flux_H (H+ number flux) depends on support_data variables energy (first dimension) and angle (second dimension). There are two ways to plot spectrograms with these 2-D data:
plot all energies (y-axis) and a few selected angle bins (in separate panels).
plot all angles (y-axis) and a few selected energy bins (in separate panels).
These are both illustrated below. Flux_H needs two label variables to adequately label all possible spectrogram displays. LABL_PTR_1 points to a label (metadata) 1-D variable H_energy_of_flux of size 28; the label variable holds 28 H+ energy labels, e.g., "H+ Flux 4.4keV/e". LABL_PTR_2 points to a label (metadata) 1-D variable H_angle_of_flux of size 12; the label variable holds 12 H+ angle labels, e.g., "H+ Flux 7.5 deg".
H+ number flux for 28 energies and 3 selected angle bins¶
The three selected angle bins appear as separate panels. The energy (support_data) variable attribute values (either the LABLAXIS value or the FIELDNAM value, along with the UNITS value) are used to label the y-axis on each panel. The energy variable is attached to the Flux_H (data) variable via the DEPEND_1 attribute.
The z-axis (color bar) is labeled with selected values from the H+ angle label variable H_angle_of_flux (metadata) that is attached to the data variable via the LABL_PTR_2 attribute. The z-axis units come from the Flux_H (data) variable’s UNITS attributes.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"Flux_H" CDF_REAL4 1 2 28 12 T T T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "data" }
"FIELDNAM" CDF_CHAR { "H+ number flux" }
"CATDESC" CDF_CHAR { "H+ number flux for for 28 energy and " -
"3 selected angle bins." }
"DEPEND_0" CDF_CHAR { "Epoch_H" }
"DEPEND_1" CDF_CHAR { "energy" }
"DEPEND_2" CDF_CHAR { "angle" }
"LABL_PTR_1" CDF_CHAR { "H_energy_of_flux" }
"LABL_PTR_2" CDF_CHAR { "H_angle_of_flux" }
"UNITS" CDF_CHAR { "#/(cm^2-s-keV/e-sr)" }
"FORMAT" CDF_CHAR { "E12.4" }
"VALIDMIN" CDF_REAL4 { 0.0 }
"VALIDMAX" CDF_REAL4 { 1.0e+08 }
"FILLVAL" CDF_REAL4 { -1.0e+31 }
"AVG_TYPE" CDF_CHAR { "standard" }
"SCALETYP" CDF_CHAR { "log" }
"DISPLAY_TYPE" CDF_CHAR { "spectrogram>y=energy,z=Flux_H(*,1),z=" -
"Flux_H(*,7),z=Flux_H(*,12)" }
"DICT_KEY" CDF_CHAR { "SPASE>Particle>ParticleType:Proton," -
"ParticleQuantity:NumberFlux," -
"Qualifier:Differential_Array" }
"VAR_NOTES" CDF_CHAR { "Negative values reflect low counting " -
"rates and background subtraction. " } .
H+ number flux for 12 angles and 3 selected energy bins¶
The three selected energy bins appear as separate panels. The angle (support_data) variable attribute values (either the LABLAXIS value or the FIELDNAM value, along with the UNITS value) are used to label the y-axis on each panel. The angle variable is attached to the Flux_H (data) variable via the DEPEND_2 attribute.
The z-axis (color bar) is labeled with selected values from the H+ energy label variable H_energy_of_flux (metadata) that is attached to the data variable via the LABL_PTR_1 attribute. The z-axis units come from the Flux_H (data) variable’s UNITS attributes.
Support_data Variables¶
Examples of Epoch Variables¶
The first example below demonstrates a support_data variable Epoch of CDF_TIME_TT2000 data type (number of nanoseconds since J2000 in Terrestrial Time with leap seconds included, see CDF User’s Guide). All the required and some recommended variable attributes are included in the description. Note that Epoch is always defined as record (time) varying, and it is attached to a data variables via the data variable’s DEPEND_0 attribute.
CDF_TIME_TT2000 data type is internally well-defined and its use is strongly encouraged for new datasets.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"Epoch" CDF_TIME_TT2000 1 0 T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "support_data" }
"FIELDNAM" CDF_CHAR { "Time since J2000" }
"CATDESC" CDF_CHAR { "Time, number of nanoseconds since " -
"J2000 with leap seconds included" }
"LABLAXIS" CDF_CHAR { "Epoch" }
"UNITS" CDF_CHAR { "ns" }
"VALIDMIN" CDF_TIME_TT2000 { 2010-01-01T00:00:00.000000000 }
"VALIDMAX" CDF_TIME_TT2000 { 2029-12-31T23:59:58.999000000 }
"FILLVAL" CDF_TIME_TT2000 { 9999-12-31T23:59:59.999999999 }
"SCALETYP" CDF_CHAR { "linear" }
"MONOTON" CDF_CHAR { "INCREASE" }
"TIME_BASE" CDF_CHAR { "J2000" }
"TIME_SCALE" CDF_CHAR { "Terrestrial Time" }.
"DICT_KEY" CDF_CHAR { "SPASE>Support>SupportQuantity:Temporal" }
In the second example, a support_data variable Epoch is of CDF_EPOCH data type. The CDF data type CDF_EPOCH is the number of milliseconds since 01-Jan-0000 00:00:00.000 (see CDF User’s Guide).
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"Epoch" CDF_EPOCH 1 0 T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "support_data" }
"FIELDNAM" CDF_CHAR { "Time since 0 AD" }
"CATDESC" CDF_CHAR { "Interval centered time tag rounded to " -
"nearest msecond "}
"LABLAXIS" CDF_CHAR { "Epoch" }
"UNITS" CDF_CHAR { "ms" }
"VALIDMIN" CDF_EPOCH { 01-Jan-1994 00:00:00.000 }
"VALIDMAX" CDF_EPOCH { 01-Jan-2020 00:00:00.000 }
"FILLVAL" CDF_EPOCH { 31-Dec-9999 23:59:59.999 }
"SCALETYP" CDF_CHAR { "linear" }
"MONOTON" CDF_CHAR { "INCREASE" }.
"DICT_KEY" CDF_CHAR { "SPASE>Support>SupportQuantity:Temporal" }
Example of 1-D Energy Variable¶
This example show definition of a time-varying 1-D (size 12) support_data variable IDiffI_I_Energy (Ion Energy at 12 channels), with all the required and some recommended attributes included. This support_data variable is attached to the same size data variable IDiffI_I (Ion Diff. Intensity at 12 energies, described here) via the IDiffI_I variable’s DEPEND_1 attribute.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"IDiffI_I_Energy" CDF_REAL4 1 1 12 T T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "support_data" }.
"FIELDNAM" CDF_CHAR { "Ion Energy (EPIC/ICS)" }
"CATDESC" CDF_CHAR { "Ion Energy, at 12 channels energies " -
"67-1361 keV (EPIC/ICS) " }
"DEPEND_0" CDF_CHAR { "Epoch" }
"LABLAXIS" CDF_CHAR { "Ion Energy" }
"UNITS" CDF_CHAR { "keV" }
"FORMAT" CDF_CHAR { "F7.1" }
"VALIDMIN" CDF_REAL4 { 67.3 }
"VALIDMAX" CDF_REAL4 { 1361.0 }
"FILLVAL" CDF_REAL4 { -1.000000e+31 }
"DELTA_PLUS_VAR" CDF_CHAR { "IDiffI_I_Eplus" }
"DELTA_MINUS_VAR" CDF_CHAR { "IDiffI_I_Eminus" }
"DICT_KEY" CDF_CHAR { "SPASE>Particle>ParticleType:Ion," -
"ParticleQuantity:Energy" }
Metadata Variables¶
Example of Magnetic Field Label Variable¶
This 1-D (size 3) metadata variable label_B_GSE holds three strings for labeling the cartesian GSE magnetic field data variable BGSE (described here), and it is attached to BGSE via BGSE variable’s LABL_PTR_1 attribute. A Character metadata must define the number of elements to be the same as the maximum number of characters used in its values, 6 in this case of six-character strings.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"label_B_GSE" CDF_CHAR 6 1 3 F T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "metadata" }.
"FIELDNAM" CDF_CHAR { "Label cartesian B" }
"CATDESC" CDF_CHAR { "Label cartesian B" }
"FORMAT" CDF_CHAR { "A6" }
! NRV values follow...
[ 1 ] = { "Bx GSE" }
[ 2 ] = { "By GSE" }
[ 3 ] = { "Bz GSE" }
Example of Time_PB5 Variable¶
time_pb5 variable is representing the time as a 1-D (size 3) integer array storing Year, Day of Year (note: January 1 is Day 1), and Millisecond of Day (elapsed ms), which allows for easy recognition of the time value when looking at the data, for instance in a data dump. This variable was part of the requirements for the ISTP Key Parameter (KP) CDF datasets only, and it is not recommended for new datasets.
To describe the time components, time_pb5 has three attached metadata variables which provide labels (label_time variable attached via LABL_PTR_1 attribute), units (unit_time attached via UNIT_PTR) and formats (format_time attached via FORM_PTR). See descriptions of these metadata variables.
! Variable Data Number Record Dimension
! Name Type Elements Dims Sizes Variance Variances
! -------- ---- -------- ---- ----- -------- ---------
"time_pb5" CDF_INT4 1 1 3 T T
! Attribute Data
! Name Type Value
! -------- ---- -----
"VAR_TYPE" CDF_CHAR { "support_data" }
"FIELDNAM" CDF_CHAR { "Time PB5" }
"CATDESC" CDF_CHAR { "Time of observation in Year, Day, & " -
"milliseconds" }
"DEPEND_0" CDF_CHAR { "epoch_1hr" }
"LABL_PTR_1" CDF_CHAR { "label_time" }
"UNIT_PTR" CDF_CHAR { "unit_time" }
"FORM_PTR" CDF_CHAR { "format_time" } .
"VALIDMIN" CDF_INT4 { 1997, 237, 0 }
"VALIDMAX" CDF_INT4 { 2030, 365, 0 }
"FILLVAL" CDF_INT4 { -2147483648 }
"DICT_KEY" CDF_CHAR { "SPASE>Support>SupportQuantity:Temporal" }
