**High Resolution Dynamics Limb Sounder (HIRDLS)**

**A Short Guide to the use and interpretation of V003**

**(HIRDLS Version 2.04.09) Level 2 data.**

**Introduction**

This document is a brief guide for those wishing to use Level 2 data
(geophysical products along the measure­ment track) produced by the
HIRDLS Version 2.04.09 data processing algorithms for the High
Resolution Dynamics Limb Sounder (HIRDLS) on the Aura spacecraft. These
are designated as V003 at the Goddard DISC and will have a designation
of V2.04.09 in the filenames.

This data version contains temperature, ozone and nitric acid mixing
ratios, and cloud top heights and characteristics. The validation of
these data is described in the papers listed in the references. The data
are evolving as algorithms are improved and extended, and it is
anticipated that future data versions will contain additional species,
as well as improved versions of the present retrieved quantities. Those
wishing to use the data should contact one of the HIRDLS PI's concerning
their intended use. Feedback to the HIRDLS team on features found in the
data is strongly encouraged.

A preliminary Data Description and Quality Document for DISC Data
Version 003 will be released shortly. This Short Guide, as well as the
Data Description and Quality Document, will be updated as newer data
versions and additional products are released.

**Reading HIRDLS Level 2 Data**

HIRDLS Level 2 data is stored in the HDF-EOS5 format in the [HDF-EOS
Aura File Format Guidelines]{.underline} document ^1^. These data files
can be read via C/C++ or Fortran using either the HDF-EOS5 or HDF5
library. A HIRDLS developed IDL routine \"get_aura\" is also available
upon request for those users which wish to use IDL to access the HIRDLS
data.

Users should obtain the pre-compiled HDF5 library for their operating
system, if possible. Otherwise, source code is also available (see
[http://hdf.ncsa.uiuc.edu](http://hdf.ncsa.uiuc.edu/)). These are
prerequisite in order to compile the HDF-EOS5 library (see
<http://www.hdfeos.org/>). Both libraries are needed to fully access the
Aura HIRDLS data files. For additional help contact the GES DISC at
[help-disc@listserv.gsfc.nasa.gov](../help-disc@listserv.gsfc.nasa.gov%20)
or telephone 301-614-5224.

Each HIRDLS Level 2 file contains one day\'s worth of data and contains
all species that HIRDLS measures. In the V003 data, a number of the
fields will be filled completely with missing values until correction
algorithms are refined for these species. For users who require only a
subset of the HIRDLS species, the Goddard DISC has the ability to subset
data before distributing it to users. Contact the DISC directly for more
information on this service.

Individual HIRDLS data values for a product are stored in fields labeled
with the species name (see Table 1 for exact names). The estimated
precision of each data point is a corresponding field named
*Species*Precision (for instance, Temperature and TemperaturePrecision).
Two additional fields for each species, *Species*NormChiSq and
*Species*Quality, are both filled with missing for V003.
CloudTopPressure does not have Precision, NormChiSq or Quality fields.

There are two time fields in the HIRDLS data file, *Time* and
*SecondsInDay*. *Time* is stored in TAI time (seconds since the epoch of
UTC 12 AM 1-1-1993). This time includes leap seconds and can cause
problems with simplistic conversions. For this reason, HIRDLS is also
storing *SecondsInDay* which is seconds since midnight of the data day.
Leap seconds do not pose a problem when using this field. Note that the
first data point may be negative which indicates a time stamp before
midnight. This is the case for scans which span a day boundary.

**Data Points to Avoid**

Data points for which more than half of the information comes from the a
priori have the precision ﬁeld set negative and should not be used for
scientific studies.

**Known Problems**

A few cloud tops are not detected, resulting in retrievals at low
altitudes of cloud- contaminated radiances. This can result in
temperatures too warm, and positive or negative spikes in species
retrievals.

While not expected, there may be some residual differences between up
and down scans. Critical features should be checked to ensure they
appear in scans in both directions.

These and other problems are discussed in more detail in the Data
Description and Quality Document (SC-HIR-1511a).

Table 1 overleaf details the useful vertical range, estimated accuracy,
and the HIRDLS team contact for each product in this version. The
vertical range and accuracy entries generally summarize complex
variations, and the listed references should be consulted before any use
of the data. Additional products may be available in future versions.

**How do I Interpret the Data?**

The HIRDLS data give a set of values of temperature or mixing ratios on
a set of pressure levels. This is described in more detail in the V003
Data Quality Document.

.

**HIRDLS PI Contact Information:**

**John Gille John Barnett**

**<gille@ucar.edu>
[j.barnett@physics.ox.ac.uk](../j.barnett@physics.ox.ac.uk)**

**Table 1: Information concerning HIRDLS standard products**.

+----------+-----------+--------+-------+---------+------------------+
| **P      | **Field   | **     | *     | **      | **Contact        |
| roduct** | Name**    | Useful | *Esti | Contact | Email**          |
|          |           | R      | mated | Name**  |                  |
|          |           | ange** | Accur |         |                  |
|          |           |        | acy** |         |                  |
+----------+-----------+--------+-------+---------+------------------+
| Tem      | Te        | 316    | ± 2 K | John    | <gille@ucar.edu> |
| perature | mperature | -\> 1  |       | Gille   |                  |
|          |           | hPa    |       |         |                  |
+----------+-----------+--------+-------+---------+------------------+
| O~3~     | O3        | 100+   | 10    | Bruno   | [na              |
|          |           | -\>    | 0-600 | Nardi   | rdi@ucar.edu](.. |
|          |           | 1.0    | ppbv, |         | /nardi@ucar.edu) |
|          |           | hPa    |       |         |                  |
|          |           |        | 5-10% |         |                  |
+----------+-----------+--------+-------+---------+------------------+
| HNO~3~   | HNO3      | 100    | 10    | Douglas | [                |
|          |           | -\> 10 | -\>   | K       | dkin@ucar.edu](. |
|          |           | hPa\*  | 30%†  | innison | ./dkin@ucar.edu) |
+----------+-----------+--------+-------+---------+------------------+
| Cloud    | CloudTo   | 422    | ± 20% | Steven  | [massie@uca      |
| top      | pPressure | -\> 10 |       | Massie  | r.edu](mailto:ma |
| pressure |           | hPa    |       |         | ssie@ucar.edu%0D |
|          |           |        |       |         | massie@ucar.edu) |
+----------+-----------+--------+-------+---------+------------------+
| *HDF5,   | *Library  |        |       | GSFC    | [Help-d          |
| H        | inst      |        |       | DAAC    | isc@listserv.gsf |
| DF-EOS5* | allation* |        |       |         | c.nasa.gov](../H |
|          |           |        |       |         | elp-disc@listser |
|          |           |        |       |         | v.gsfc.nasa.gov) |
+----------+-----------+--------+-------+---------+------------------+
| *H       | *Reading  |        |       | Cheryl  | [cacrai          |
| DF-EOS5* | HIRDLS    |        |       | Craig   | g@ucar.edu](../c |
|          | data*     |        |       |         | acraig@ucar.edu) |
+----------+-----------+--------+-------+---------+------------------+

\* Depends on latitude

† Varies with latitude and altitude. See Kinnison et al.

References

Gille et al., (2008), The High Resolution Dynamics Limb Sounder
(HIRDLS): Expermient Overview, Results and Validation of Initial
Temperature Data, *Journal of Geophysical Research*; submitted.

Kinneson et al., (2008), Global Observations of HNO3 from the High
Resolution Dynamics Limb Sounder (HIRDLS) -- First Results, *Journal of
Geophysical Research*; submitted.

Massie et al., (2008), Validation of HIRDLS Observations PSC's and
Subvisible Cirrus, *Journal of Geophysical Research*; in press.

Nardi et al., (2008), Validation of HIRDLS Ozone Measurements, *Journal
of Geophysical Research*; in press.