Using NASA`s Giovanni System to Detect and Monitor Saharan Dust

Using NASA’s Giovanni System to
Detect and Monitor
Saharan Dust Outbreaks
James G. Acker
NASA Goddard Earth Sciences Data and Information Services Center
African Dust Workshop 2011
Part 1: Introduction to Giovanni
First, let’s clear up some misconceptions. Giovanni is not:
an Italian astronomer
a boy band (like Menudo)
a restaurant in Baltimore’s Little Italy, or
an unfinished Mozart opera.
So, then, what IS Giovanni?
Giovanni used to stand for the Goddard Earth Sciences Data and Information
Services Center (GES DISC) Interactive Online Visualization ANd aNalysis
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
Select Plot type
Generate Visualization
Outputs: Refine/Modify
Refine constraints, and
edit plot preferences
Giovanni data download page
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
Choosing a region-of-interest
Choosing a data product
& time period
Data product
Time period
Choosing the visualization option
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?
Giovanni produces this:
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
Back to the Giovanni interface…
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:
which produces this:
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.
Deep Blue AOD,
March 1-5, 1994
Approximate location of
the Bodélé Depression
Deep Blue AOD animation frames,
March 1-4, 2004
March 1
March 3
March 2
March 4
Deep Blue AOD animation frame
March 5, 2004
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
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,
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.
Advanced: Latitude vs. Time
Hovmöller plot
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
this region between
March 1st and March
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
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 QualityRelated 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
growth here might
be augmented by
iron from dust

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