All of the questions below are linked to descriptive answers in this chapter of the Giovanni-3 Online Users Manual regarding the Giovanni-3 AIRS instance. Click the question of interest.
What is AIRS?
AIRS stands for Atmospheric Infrared Sounder. AIRS is an instrument on the EOS Aqua satellite, launched in 2002.
What is the current version of the data available in the Giovanni-3 AIRS instance?
The most recent version, V005.
For the monthly AIRS instance, the portal includes the mid-tropospheric CO2 retrieval and standard retrieval parameters:
For the daily AIRS instance, the standard retrieval available:
What AIRS data types are available in this instance?
There are actually two AIRS instances available now in Giovanni. The data types available in the monthly instance are global gridded data (Level 3) for 1.0° x 1.0° areas, averaged (binned) over monthly intervals. The data types available in the daily instance are global spatially-gridded (Level 3) for 1.0° x 1.0° areas. Both of these gridded data products are derived from the AIRS profile data.
Which AIRS data parameters are available for analysis in Giovanni-3 AIRS?
Note that all data parameters are available for both ascending node [the point at which an orbiting body rises through the plane of the ecliptic traveling northward] and descending node [the point at which an orbiting body rises through the plane of the ecliptic traveling southward]. The standard AIRS data parameters are:
Layers versus Levels, in AIRS vertical profiles
AIRS humidity profiles, that is parameters that start with "H2O", and "RelHumid", and have the notation (3D), are LAYER variables; they represent the mean value of the corresponding entity in the layer enclosed within indicated levels; e.g. a humidity entity selected at 500 mb represents the mean quantity in the layer 500-400 mb.
Users should distingusih them from the temperature profiles, where data are reported at the effective LEVEL as shown in the portal. Users are encouraged to familiarize with AIRS documentation on Layers and Levels.
Note, it is well documented that AIRS is insensitive to water vapor at less than 15-20 ppm (0.015-0.020 g/kg). AIRS reports values at altitudes of 200 hPa and above, but the sensitivity is suffering. Even though Giovanni supports water vapor data exploration at altitudes above 100 hPa, these values should not be used for analysis. Data analysis for water vapor should stop at the layer bounded by 200 hPa and 150 hPa, thus reporting for the limiting pressure of SQRT(200*150) = 173.2 hPa. Even that value should be viewed with a grain of salt. Beginning with the next layer down, SQRT(250*200) = 223.6 hPa, the AIRS sensitivity to water vapor is beginning to be reasonable.
- Fetzer, E. J., W. G. Read, D. Waliser, B. H. Kahn, B. Tian, H. Vömel, F. W. Irion, H. Su, A. Eldering, M. de la Torre Juarez, J. Jiang and V. Dang (2008), Comparison of upper tropospheric water vapor observations from the Microwave Limb Sounder and Atmospheric Infrared Sounder, J. Geophys. Res., 113, D22110, doi:10.1029/2008JD010000.
- Read, W. G., A. Lambert, J. Bacmeister, R. E. Cofield, L. E. Christensen, D. T. Cuddy, W. H. Daffer, B. J. Drouin, E. Fetzer, L.Froidevaux, R. Fuller, R. Herman, R. F. Jarnot, J. H. Jiang, Y. B. Jiang, K. Kelly, B. W. Knosp, L. J. Kovalenko, N. J. Livesey, H.-C. Liu, G. L. Manney, H. M. Pickett, H. C. Pumphrey, K. H. Rosenlof, X. Sabounchi, M. L. Santee, M. J. Schwartz, W. V. Snyder, P. C. Stek, H. Su, L. L. Takacs, R. P. Thurstans, H. Voemel, P. A. Wagner, J. W. Waters, C. R. Webster, E. M. Weinstock and D. L. Wu (2007), Aura Microwave Limb Sounder upper tropospheric and lower stratospheric H2O and relative humidity with respect to ice validation, J. Geophys. Res., 112, D24S35, doi:10.1029/2007JD008752.
- Gettelman, A., et al. (2004), Validation of Aqua satellite data in the upper troposphere and lower stratosphere with in-situ aircraft instruments, Geo-phys. Res. Lett., 31, L22107, doi:10.1029/2004GL020730.
How are data parameters selected for analysis?
Individual parameters are selected by clicking in the check boxes. An entire group may be selected by clicking the group box (leftmost column heading bar, next to the collection name and date range information). If this selection is performed, individual parameters may then be deselected by clicking in the appropriate check box(es).
What are the current data analysis and visualization (output) capabilities in Giovanni-3 AIRS?
There are currently ten data analysis and visualization services in Giovanni-3 AIRS, listed below. Atmospheric profile visualization capability willl be added in the near future.
How is the spatial area of interest selected?
The spatial area of interest can be selected by either of the two methods described below
Java applet map: The Java applet map can be utilized to "click and drag" a selection box to designate the spatial area of interest.
Geographic coordinates: The geographic coordinates of the corners of the spatial area box can be input individually. This method can be used if Java is not enabled. Note that decimal and not degree (seconds and minutes) coordinates must be entered.
How is the time range of interest selected?
The starting date (year/month/day), and the ending date (year/month/day) for the analysis are selected using the calendrical menus on the Giovanni interface page. Error messages will be generated if the beginning month or the end month are out of the data set time range, or if the end month is before the beginning month. Note that the time ranges are shown for each data set. Because the AIRS data sets comprise different mission time ranges, be careful to select a time range appropriate for the data set for which the data visualization is being requested.
Are there any limits on the spatial area or time range that can be selected?
No. Longer time ranges will take considerably more time for initial data acquisition from the archive (fetching) and may require a longer period of elapsed time for processing. Also, the time range for which data can be requested is limited by the time range of the data set itself (see question immediately above).
What are the plotting preference options for the data visualizations in Giovanni-3 AIRS?
The plotting preference options are described in the Plot Preferences section of the Online Users Manual.
After the initial output has been generated, the temporal and spatial ranges (constraints) and plotting preferences can be changed, and a new output generated, using the "Submit Refinements" button.
Why are there so many AIRS data parameters?
AIRS was designed to be capable of measuring many different atmospheric variables that are of interest to both meteorologists and climate scientists. AIRS collects data on both the day side and the night side of the Earth (the ascending and descending nodes of the Aqua satellite orbit), and because the dynamics of the atmosphere change between day and night, the ascending node and descending node parameters can be significantly different. So AIRS provides a large amount of data for scientists to use.
What would be the most interesting AIRS data parameters to look at?
The "interesting" parameters can depend on a person's field of study or interests. For meteorologists, the cloud data parameters, water vapor, and relative humidity are useful to examine. For climate scientists, the atmospheric temperature and atmospheric pressure data may provide insight into climate processes. Atmospheric chemists could use the parameters measuring methane, ozone, and carbon monoxide. In an article about Giovanni published in the American Geophysical Union's weekly newspaper Eos, we looked at dust with MODIS data and used an AIRS relative humidity profile to determine the approximate altitude of the air mass carrying the dust from the desert over the Atlantic Ocean.
How was the climatology in the AIRS monthly instance created?
The climatology in the AIRS monthly instance is analogous the the corresponding monthly mean parameter except that it includes data for that month from 8 years of AIRS observations. For example, the September climatology is the arithmetic mean of observations taken over 8 Septembers from 2002-2009. These climatolgies can be used to calculate anomalies of the corresponding monthly mean parameters.