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ASPEN



Aspen






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Aspen (the Atmospheric Sounding Processing ENvironment) is used for analysis and quality control (QC) of sounding data. The application functions identically in the Linux, MacOS, and MS Windows environments.

Capabilities

Automatically apply quality control procedures to sounding data.

Present data in tabular and graphical forms.

Automatically determine levels and code them in WMO message formats.

Transmit the WMO messages to other systems.

Save the raw and derived data products in various formats.

Present observations from multiple soundings, at discrete pressure levels, on a synoptic map.


Aspen can process data provided in many formats, including AVAPS Dropsonde, NCAR EOL, HRD FRD, and WMO TEMP formats. It is able to analyze both dropsonde and upsonde soundings.

Aspen is designed to operate as automatically as possible, while allowing the user to fine tune the quality control algorithms. For instance, as soon as the user selects a sounding file for processing, the data is brought into Aspen and automatically analyzed. In most cases this first pass will be the only step required. If the processing needs to be modified, the user can change the QC parameters and reprocess the data as many times as necessary.

An extensive series of QC algorithms is applied to the data. These algorithms typically have one or two parameters that may be adjusted by the user if the default values are not suitable for a particular sounding. The user can save the modified options, so that the initial analysis of a new sounding will use the customized QC parameters.

Aspen can have a large number of input files open at the same time. This makes it convenient to compare soundings. Output results can be formatted as printed text and graphics, and saved in graphics, ASCII, CSV, and netCDF files.

The synoptic map capability is particularly useful for detecting anomalous observations during operational sounding activities. It allows a collection soundings to be compared from a geographic perspective. This can very quickly reveal discrepancies in calculated pressure heights and other sensor malfunctions.

History

Aspen is derived from the Editsonde software developed at the National Hurricance Center's Hurricane Research Division (HRD). It has progressed through four versions:

V1 - The Fortran Editsonde package was wrapped in Visual Basic, in order to provide a graphical interface and MS Windows compatibility.

V2 - The entire package was rewritten in C++, with graphics implemented using the Microsoft Foundation Classes.

V3 - The graphics were ported to the Qt toolkit, in order to support Linux, OSX and MS Windows, using an identical code base.

V4 - The package was significantly updated to work with the next generation ACS dropsonde control software.

Aspen version 4 is the current release, and is under active development. The current release series is V4.1. 

Command Line Versions (Aspen-QC)

The Aspen quality control processing can also be performed by a command line program, which does not provide a graphical user interface. This program is named Aspen-QC, to signify that it only performs the quality control processing, without providing a user interface.

The output products are specified with command line switches. This can be useful for scripted processing, but as always with automated processing, care must be taken to validate the results.

The quality control parameters are specified in the aspen.xml file, which is same underlying configuration mechanism used by the graphical version of Aspen. The most convenient way to modify these parameters is to run Aspen and use its configuration editor to change parameters, and then copy that aspen.xml file to the directory containing the Aspen-QC program. The directory containing aspen.xml is shown in the status bar at the bottom of the Aspen display.

Documentation and Help

The user manual is accessible from within the Help menu when running Aspen. Its content is also hosted online:

AspenDocs documentation site

For help or questions, please contact eol-aspen[at]ucar[dot]edu.


Citation

When referencing the NCAR/EOL ASPEN software in publications or presentations, please use the citation:

Martin, C. and Suhr, I. (2026). NCAR/EOL Atmospheric Sounding Processing ENvironment (ASPEN) software version 4.0.6. https://doi.org/10.26023/3MXP-4C54, 2026.

Please update the access date and the software version you used in the citation. 





Main content




ASPEN Versions


For Aspen version 4.0.0 and up, use the accordion menu below to download the appropriate installer for your operating system or view release notes and changes for that version.

Please contact us if you need older Aspen versions or information about previous version history.






4.1.1 - May 6, 2026





RedHat/Alma 9Windows 10/11MacOS Sequoia (ARM)MacOS Sonoma (Intel)


Note: some Mac users report the download links returning the wrong file type when using Safari. To fix this, download with another browser, or manually change the downloaded file back to .dmg.


fix library issues when running Aspen-QC

add Aspen DOI information to info box

add filter to open specifically .nc files for ACS, set as the default in the mini-dropsonde config set

update RH buddy slope to 3% in the mini-dropsonde config set

add REL and SPG locations to Summary tab









4.1.0 - Jan 4, 2026





Released in a Windows build for the Air Force only (for the 2026 hurricane season).




Update graphics library to Qt6 on all platforms.

Fixes for legibility when using dark mode.

Remove unmaintained print and print preview options from all tabs. Data can be exported by saving files, or GUI state can be recorded by taking screenshots.

Set default config set to mini-dropsonde to match current operational use.

Fix crash when all wind data is missing or ignored.









4.0.6 - Jun 17, 2025





CentOS 7


Build environment tweaks to build on CentOS 7

No functional change from V4.0.5.









4.0.5 - Jun 16, 2025





CentOS 8CentOS9/Alma9
MacOS 14 (Sonoma) - Apple M1

also compatible with Sequoia

MacOS 14 (Sonoma) - Apple Intel

also compatible with Sequoia
Windows 10/11


Update default wind smoothing wavelength (to 5s) for mini-dropsonde config set

Update default sonde mass (to 169g) and drag coefficient (to 0.57) for mini-dropsonde config set

Fix default values in the Aspen-supplied stock configuration XML so parameter settings will be the same between installing Aspen on a fresh system and when resetting to defaults from the Configuration menu









4.0.4 - May 5, 2025





Centos 8Centos9/Alma9
MacOS 14 (Sonoma) - Apple M1

also compatible with Sequoia

MacOS 14 (Sonoma) - Apple Intel

also compatible with Sequoia
Windows 11


Add check to remove RH values that do not have an associated temperature at the end of QC processing

Remove logic to retain the last point in each data series, even if it failed CRC check

Add buttons to set Skew-T display bounds to preset values for common aircraft altitudes

Add minimum equilibration time threshold of 6 seconds for temperature and RH equilibration calculations

Add configuration set name to Summary tab

Update autosaved WMO text (in addition to the WMO tab display) when the user makes modifications in the Comm tab

Add a User Modifications section to the Summary tab to record manual QC changes during processing

In Main tab, log ignored or overridden launch parameters, changes to dropsonde hit surface or surface altitude unknown checkboxes, surface altitude or pressure overrides, heights set to missing, and end of drop time overrides

In Raw tab, log changes to end of drop time, and points flagged as keep or ignore

In Comm tab, log the sonde environment set by the user (if present)

The user modifications text section is also added to global attributes in netCDF and CSV output, with one caveat: due to Aspen architecture limitations, netCDF and CSV data will not be updated when the user modifies the sonde environment in the Comm tab, unless the user manually recomputes










4.0.3 - July 26, 2024





MacOS 13 (Ventura) - Apple Intel


Updates to build on MacOS Ventura









4.0.2 - Jun 7, 2024






CentOS 8Alma 9MacOS 14 (Sonoma) -Apple IntelMacOS 14 (Sonoma) - Apple M1Windows 10





Add user settable option for whether to discard sonde frames with the wrong sonde ID in ACS files

Flag lines with the wrong sonde ID (ACS files only) in the Raw tab, and collect stats on number of bad lines









4.0.1 - May 10, 2024





CentOS 8Alma 9MacOS 14 (Sonoma) - Apple IntelMacOS 14 (Sonoma) - Apple M1Windows 10


Add trajectory plot option for Lat-Lon XY Graph tab: added Lat as default Y axis for this plot

Add ability to select entire columns in the Raw tab by clicking the column headers

Add Ctrl+E keyboard shortcut (Cmd+E on Mac) to jump to the end of the data tables in the Raw and QC tabs

Add warning popup about sonde size not matching config set when opening ACS netCDF files

Add clearer error text when attempting to read in an Aspen output netCDF

Add command line option to set end of drop time in Aspen-QC

Update logos for Aspen V4

Use GPS altitude in second altitude column in FRD output files; update column header accordingly

Fix bug in calculating time of synthetic surface observation that led to coding lowest winds instead of surface winds in TEMPDROP

Update mixing ratio equation to be more precise

Assorted static code analysis fixes and improvements









4.0.0 - Feb 1, 2024





CentOS 8MacOS 14 (Sonoma) - Apple IntelMacOS 14 (Sonoma) - Apple SiliconWindows 10


Support for ingesting netCDF ACS files

Add input option to read data from ACS format netCDFs

Select aircraft observation from continuous series after possible launch time corrections (if entire aircraft data set is included)

Use WMO sonde types for RD41 and NRD41 (in BUFR only) now that input files contain enough metadata to tell them apart

Add sonde model metadata to netcdf and csv output as well

Remove times from input file that are not monotonically increasing, rather than rejecting the entire file


Turn off XY graph autoscale for wind direction by default

Fix bug in calculating MB110 group for upsondes

Fix bug where launch PTH didn’t get correctly removed when ignored if there was no aircraft geopotential altitude

Fix bug where overriding and then clearing launch altitude would result in an altitude of -999 if original launch altitude was missing

Miscellaneous compilation warning fixes and code cleanup














Operating System


Windows

Mac

Linux






Application


Visualization and quality control of upsonde and dropsonde radiosonde soundings. Command line, batch and GUI based interfaces are available. For support questions, email eol-aspen(at)ucar.edu.








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This material is based upon work supported by the NSF National Center for Atmospheric Research, a major facility sponsored by the U.S. National Science Foundation and managed by the University Corporation for Atmospheric Research. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the U.S. National Science Foundation.







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