Figure 1. OMNIWeb System Diagram
For example, see this 10K GIF image for a sample time series plot created with OMNIWeb.
A brief article "New Access to OMNI Data Through the World Wide Web" about OMNIWeb is available in the NSSDC Newsletter.
A control panel comprising four graphic buttons are present near the bottom of every "page". The control panel, in conjunction with the "back" button on WWW browsers, allow the user to navigate the OMNIWeb system.
Figure 1. OMNIWeb System Diagram
To use the OMNIWeb Data Explorer, follow the steps below:
Enter start and stop dates (use yymmdd or yyddd format)
The start and stop dates indicate the time period of interest. The dates can be entered in the following date formats:
YYMMDD
YYDDD
For example, January 1, 1992 equals 920101 in YYMMDD format and 92001 in YYDDD format. The availability of the data for magnetic field and plasma parameters is available in the data document.
The data is stored as hourly averaged values (24 records per day), which is the default resolution to access. The user may also request daily averaged values to compute the average over every 24-hours of data into a single value. This is useful for trend analysis of large periods of time. Daily resolution is only available in plots and ASCII listings.
Basic Plotting
Basic Retrieving
Advanced Plotting
Please see the Advanced Plotting document for more information about advanced plotting features.
The engine of the plotting software is a product from Research Systems Inc. called the Interactive Data Language (IDL). IDL is run in batch mode from which plots are created from the user's selections and written to a GIF file as output. Further information on IDL is available from RSI's Home Page.
The basic plotting options will generate a 640x480 image of the selected options as an inline GIF and the advanced options allow many other features to customize the plots.
Note that by selecting daily resolution, the hourly data will be averaged for each day. Further averaging and smoothing can be done using the NSUM and SMOOTH options from the advanced plotting options.
Much of the plot formatting is done automatically. For example, the axis labeling is determined "optimally" for what is determined as most appropriate. The x-axis tick marks are labeled as time (HH:MM) if the selected time period is less than 48 hours, day of month (DD) if the period is less than two months, month/day (MM/DD) if the period is less less than two years, and month/year (MM/YY) for longer periods.
The time and date are stored in each record as a CDF_EPOCH data type variable, which is a 8-byte double precision floating point value measured in milliseconds since the epoch. This variable is included automatically in all listings and retrieved data files. It will be displayed in the format dd-mmm-yyyy hh:mm where
dd is the day of the month, 1-31,
mmm is the month, Jan, Feb, Mar, ..., Dec,
yyyy is the year, AD,
hh is the hour, 0-23, and
mm is the minute, 0-59.
If the download option is chosen, the user has the additional option of converting the data to one of the formats listed below. The binary formats include the machine-independent NSSDC Common Data Format (CDF). Further information on CDF is available from the CDF Home Page with the URL http://nssdc.gsfc.nasa.gov/cdf/cdf_home.html.
Note that daily resolution values are displayed in listings and plots for browsing long time periods, but not in generated CDF or binary files. All downloaded CDF and raw binary files will be in hourly resolution, which are intended for further analysis.
The following data formats are available for when retrieving data.
The ASCII listing for downloading is more compact than the listing to terminal because it excludes any headers or labels and is more appropriate for large listings. Note that the ASCII listing formats the data values to strings, so some rounding may be involved for floating point numbers. Therefore, anyone concerned with maintaining the integrity and precision of the original data should obtain a CDF or binary data file.
The requested subsetted data files for downloading are created on the NSSDC anonymous ftp server. Data can either be transferred one at a time by clicking on the hyperlinks as they are shown or all at once by FTP'ing to nssdc.gsfc.nasa.gov and getting all the files from the user's directory. All files are uniquely named (with spacecraft code followed by process ID; e.g., "he1_8402.cdf") so that no files will be overwritten. The data files will be removed after 48 hours, so users must copy the files to their machine within that time.
For information on the spacecraft and data, please see the OMNIWeb Data document.
Further enhancements to the OMNIWeb system will be primarily driven by user requests. From our user's requests, we have added many advanced browsing options to improve our data browsing service.
For information on OMNI data, please see the OMNIWeb Data document.
Question 1: How can I know if IMP is in the tail or in the solar wind?
Answer 1: Since 1973 through the present, when we've had solar wind data from IMP-8 and another s/c for any given hour, the IMP-8 data was selected for inclusion in OMNI. Thus, any hour for which IMP-8 field/plasma data are contained in OMNI is an hour for which IMP is in the solar wind, beyond the bow shock. Three extra points -
The magnetic field PI and the plasma PI made separate determinations, based on looking at their higher resolution data, when they thought IMP-8 was beyond the bow shock. There was almost always, but not always, agreement. NSSDC did not try to make an independent judgement when the PIs disagreed; we included in OMNI whatever each PI provided as being in the solar wind. Over the past couple of years, there has been more effort to agree.
The energetic particle data from IMP-8 included on OMNI is taken in the solar wind part and non solar wind parts of the orbit.
NSSDC typically provides to Helen Coffey at NOAA/Boulder predicted IMP-8 solar wind times a year at a time, about 6-123 months before the start of a year.
Answer 2: Gaps indicate missing data for that time period. The data flag parameter may shed light on the availability; e.g., if the data flag value is 5 then there is no Plasma or IMF data for that record, so the data is invalidated and the data point for that time is not be plotted. (See data document for a description of the data flag.)
Answer 3: IMP-8 was the only spacecraft monitoring the near-Earth solar wind in 1990. Unfortunately IMP-8 is out of the solar wind for 4-5 days of every 12 day orbit, and does not get complete coverage for the 7-8 days per orbit that it is in the solar wind.
Answer 4: The first hourly average of any given day is accumulated from available fine time scale points observed between 0000UT and 0100UT of that day.
V0.9 7-Nov-94 SST - Prototype Help document. V1.0 11-Dec-94 GJM - Added error description sections. V1.1 15-Dec-94 SST - Updated/reorganized help file. V1.2 12-Jan-95 GJM - Updated to follow HTML 2.0 specs. V1.3 21-Feb-95 SST - Created User Questions and Answers section. V1.4 1-Mar-95 GJM - Added What's New and Advanced options sections. V1.5 13-Mar-95 SST - Added list of user feedback. V1.6 19-Apr-95 GJM - Updated availability dates. V1.7 18-Jan-96 GJM - Updated availability dates. V1.8 28-Jun-96 GJM - Moved OMNI data section into a separate document.
