James G. Acker
NASA Goddard Earth Sciences Data and Information Services Center
(GES DISC)
African Dust Workshop 2011

First, let’s clear up some misconceptions. Giovanni is not : a) an Italian astronomer b) a boy band (like Menudo) c) a restaurant in Baltimore’s Little Italy, or d) an unfinished Mozart opera.
So, then, what IS Giovanni?

Giovanni used to stand for the G oddard Earth Sciences Data and Information
Services Center (GES DISC) I nteractive O nline V isualization AN d a N alysis
I nfrastructure.
But we just call it “Giovanni” now.
 It’s a Web-based application developed by the NASA GES DISC
 It’s easy to use
There’s no need to learn data formats, programming, or to download large amounts of data
 You get customized data analyses and visualizations with only a few mouse clicks.

Main Elements of Giovanni
 Interactive map for region-of-interest selection
 Compendium of available data products for analysis
 Calendrical selection of time period of interest
 Menu of visualization options

Getting Started with Giovanni
Select Area of Interest
Select Display (info, unit)
Select Parameters
Select Time Period
Se lect Plot type
Generate Visualization

Outputs: Refine/Modify
Refine constraints, and edit plot preferences

Giovanni data download page
HDF, NetCDF, ASCII
Visualization image is here

Part 2: Finding Saharan Dust Outbreaks
In this section, the use of the Giovanni system to find occurrences of Saharan dust outbreaks will be demonstrated.
You will learn how to:
• Choose a region-of-interest
• Choose a time-period of interest
• Select a data product for visualization
• Select a visualization option
• View and interpret the generated visualization
• Save the visualization

Choosing a Giovanni
Data Portal
We’re going to have a better, easier-to-use Giovanni home page very soon.
So now, we’ll choose the MODIS Daily data portal.
The MODIS Daily data portal has:
MODIS Terra and Aqua Daily Level-3 Data
Atmosphere Daily Global 1X1 Degree Products

ZOOM

Data product selection
Time period selection

In this case, the “Time Series” option is selected from a drop -down menu.
In these steps, we have selected:
 The coast of northwestern Africa as the region-of-interest;
 The data parameter - Aerosol Optical Depth at 550 nanometers from MODIS
 The time period January-August 2004
 The time-series visualization option
So what happens when “Generate Visualization” is clicked?

To save any image, right-click and “Save Image As” or “Save Picture As”, or the equivalent
The other peaks indicate smaller dust storms

Part 3. Visualizing (and Interpreting)
Images of Saharan Dust Outbreaks
Now that Giovanni has helped find a large Saharan dust outbreak in early March 2004, the next step is to use
Giovanni to see what it looked like, according to the data.

But first… what did it look like from space?
MODIS pseudo true color image of Saharan dust outbreak,
March 2004

Adjust the region-of-interest slightly:
Select the “Lat-Lon map, Time-averaged” option (very popular):

MODIS Aerosol Optical Depth at 550 nm,
March 5, 2004

Now change the Plot Preferences:

Other color palette choices

New data parameter:
MODIS “Deep Blue” AOD
The MODIS “Deep Blue” aerosol optical depth data parameter allows retrieval of AOD values over bright land areas, where the standard AOD algorithm fails.
Using “Deep Blue” AOD, the source areas of Saharan dust outbreaks which migrate over the Atlantic Ocean can be observed.

Approximate location of the Bodélé Depression

March 3
Deep Blue AOD animation frames,
March 1-4, 2004
March 1 March 2
March 4

MODIS AOD, March 5, 2004

Tracking Saharan Dust Outbreaks
Using Aerosol Optical Depth and adjusting its “sensitivity”, the impact of a Saharan dust outbreak over the tropical
Atlantic Ocean can be tracked.
Leading edge MODIS AOD for the period March
5-15, 2004, using
1.5 as the upper bound value for the color palette.

Tracking Saharan Dust Outbreaks
Upper bound value for AOD palette is now set to 0.5.
It now appears that elevated
AOD from the dust is affecting the West Indies.

Tracking Saharan Dust Outbreaks
Same color palette range is used here; now for the period
March 15-20,
2004.
Higher values of
AOD over the
West Indies (and even Puerto
Rico), and notably on the northeast coast of
South America.

Where is the Saharan dust in the atmosphere?
Employing the Atmospheric Infrared Sounder (AIRS) Daily data portal, we can examine the atmospheric environment of the Saharan dust outbreak.

Where is the Saharan dust in the atmosphere?
Choose Vertical Profile Layers
Choose Vertical Profile option

Where is the Saharan dust in the atmosphere?
Dry air layer
The relative humidity profile shows the dry air layer primarily between 500-600 hPa, which is 4200-5600 meters, or
13,000 – 18,000 feet.
The temperature profile doesn’t provide as much information.

Where is the Saharan dust in the atmosphere?
Mapping relative humidity in the 500 hPa layer shows the horizontal extent of the dry air layer.

As a guide, 36° N is the latitude of the
Straits of Gibraltar, and 6° N is about the latitude where the
West African coast turns westward.
The Hovmöller plot shows occurrences of dry air off the
“Saharan” coast. The dust storm we have been examining impacted this region between
March 1 st and March
23 rd .
Latitude

Impacts on the Caribbean Sea?
We can examine chlorophyll a and sea surface temperature for February, March, and April 2004 – but there are complicating factors.
The data portal used here is the Ocean Color Radiometry portal.
Later this year we will have 8-day (rather than monthly) data, allowing
Better discrimination of shorter-term effects. We will have both
Standard Ocean Color Radiometry data parameters, and Water Quality-
Related parameters, including optical properties and Euphotic Depth
(1% light level).

Impacts on the Caribbean Sea?
February 2004

Impacts on the Caribbean Sea?
March 2004

Impacts on the Caribbean Sea?
April 2004
Phytoplankton growth here might
be augmented by iron from dust