This study analyzed the correlation between aerosol optical depth and total column water vapor near the coast of Africa using satellite data from OMI and reanalysis data from ECMWF. The results showed: 1) In October 2009 and 2010, there was a consistent positive correlation between the two factors. 2) In January 2009, the correlation was weak and inconsistent, with most data points clustered on one side. 3) During a dust storm in March 2010, there was an indirect negative correlation between aerosols and water vapor. The results refute the "semi-direct effect" hypothesis that absorbing aerosols warm clouds and increase humidity. Further research is needed to better understand the relationship between aeros

1. INTRODUCTION
Correlating Aerosol Optical Depth and the Total
Column Water Vapor Near the Coast of Africa
-Aerosols are tiny suspended particles in the
atmosphere that have the potential for creating
a big impact on climate.
It is important to study aerosols because aerosols
can act as a site for chemical reactions. The
semi direct effect, first suggested by S.
Twomey, is another hypothesized effect of
aerosols. Aerosols warm the layer of cloud in
which they are located, which leads to a
decrease in relative humidity as well less cloud
cover.
 The strongest moisture increase is found in
the high-dust regions in summer, whereas
moisture and relative humidity decrease
even for strongly absorbing dust in the
high-dust regions in winter.
 The net increase in relative humidity for
absorbing dust in the high-dust regions in
summer is due to the overwhelming effect of
the increase in water vapor, which is larger
than the relative humidity decrease due to the
temperature change.
MATERIALS &
METHODS The reanalysis data in NetCDF format was
downloaded from the ECMWF online data
service and read on Excel.
 Using Panoply software downloaded from
the NASA website, the data was made into
color maps.
 Data from the color maps were used to
pinpoint a specific location in which high
levels of aerosol content and water vapor
levels were seen.
 The satellite data was retrieved from OMI
through the online download process in HDF5
format.
 With Excel, graphical and statistical analyses
were performed.
RESULTS
DISCUSSIONABSTRACT
Tahsina Islam
ACKNOWLEDGEMENTS
I would like to thank my teacher, Dr. Julie Mankiewicz of
the Bronx High School of Science, for the patience, sacrifice
and guidance she gave for this project. I would also like to
thank my mentor, Dr. Jan Perlwitz from the NASA Goddard
Institute for Space Studies at Columbia University, for
teaching me everything I know.
High absorbing aerosol levels as well as water vapor
levels were found with in West Africa, mostly due to
biomass burning. Aerosols can directly change the cloud
cover through direct means of radiation as well as
indirectly through microphysical interactions between
water droplets and aerosol particles. The semi direct
effect is also a claim supported by many climate models.
In this study, the correlation between aerosol optical
depth and the total water column vapor is analyzed from
observational data. Data taken from the OMI Aura
satellite of the aerosol optical depth from coast of West
Africa was compared to the reanalysis taken from the
ECMWF station of the total column water vapor. A
correlation analysis was done from various periods to
understand the relationship on smaller scale. Results
show very little correlation between the two factors
showing a possible lack of correlation and even a lack of
the semi direct effect at this scale.
From the correlation analysis, it is seen that there is not
much of a relationship between the total column water
vapor levels and the absorbing aerosol optical depth for
the month of January, while there was a more consistent
correlation in October.
 This could be that other environmental factors may have
led to an indirect relation between the two factors
instead the direct one that was expected (Perlwitz, 2009).
 Because the magnitude of the effect of absorbing
aerosols are not yet known (Schulz et al., 2006;
Ramanathan and Carmichael, 2008), there was no level
of correlation that was expected.
 But because previous models have shown a positive
correlation (Perlwitz et al, 2009), much of the results
refute the hypothesis.
 The reason behind the fact that January had both an
inconsistent correlation as well as low values might be
from the fact that during those months, there was
insufficient humidity for the aerosols to have an effect at
all.
y = 5.4092x - 1059.7
R² = 0.0346
-8000
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0
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10000
0 100 200 300 400 500 600 700 800
ECMWFReanalysistwcv
OMI AOD 342 nm
Correlational Analysis Jan 1-31 2009
y = 6.1386x + 348.8
R² = 0.0608
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0
2000
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0 50 100 150 200 250 300 350 400
ECMWFReanlysisoftcwv
OMI AOD 342 nm
Correlational Analysis October 1-31 2010Absorbing Aerosol Optical Depth taken form the OMI Aura satellite: at 342.5 nm
wavelengths during January 1st, 2006 to January 1st, 2007. Part of South America and
West Africa is observed to have large amount of aerosol optical depth as well as China.
y = -7.6151x + 11875
R² = 0.0909
0
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ECMWFReanalysis
OMI AOD 342 nm
Correlational Analysis Dust Storm March 2010
Mapped reanalysis data showing total water vapor levels: from January 1st
2006 to January 1st, 2007. A concentration of total water column levels are seen in
West Africa, South America as well as a large portion of Southeast Asia.
1
October: In October there is a more of an apparent correlation. In
both the years 2009 and 2010, the correlation analysis showed
consistency because both years had positive correlation.
By looking at the color maps of the absorbing aerosol regions in
Africa (Figure 1 and 2), the area chosen from these map is a
small area of the country Cameroon because of the high
concentration of aerosols there. To assess to which months to
look further into, month with high wet days as well as low wet
days in order to understand the effect absorbing aerosols have.
Study Area: An area spanning from 0 to 3 N and from 10 E to 15 E is
chosen for the analysis. This image zooms in for a clearer of view of the
area used .
2
3
In January 2009, the correlation was a positive value of 0.0346.
The correlation is not very apparent as more of the points are
focused on one side4
5
 Further research could expand on the time frame used
and look more closely at months with both high and low
temperatures.
 In order to study the full climatic effect aerosols have,
it is important to look at all the components involved
which also include heat and humidity.
March 21: dust blows out westward over the Atlantic Ocean: A
dust storm hit West Africa in mid-March, 2010.. This time period
was analyzed to see if there was a relationship when dust levels
were high.
Dust Storm Analysis: The correlation between the total water
column vapor and absorbing aerosols of March 2010. In the month
when there was a dust storm, the correlation is negative. This shows
that when there are higher levels of aerosols, the effect becomes
indirectly proportional.
6
7
 The results have shown that that while the analysis of
October correctly showed the hypothesis, the analysis of
January did not.
 During the dust storm, the results showed an indirect
relationship between aerosols and water vapor. Much
like the January results, this leads to refute the semi
direct hypothesis.
 These results suggest that further studies and
attempted correlations in other parts of the world
and in other climatic conditions are warranted.
FURTHER RESEARCH
CONCLUSIONS
CITATIONS
Perlwitz, J.P., and R.L. Miller (2010), Cloud cover increase
with increasing aerosol absorptivity - A counterexample
to the conventional semi-direct aerosol effect. J.
Geophys. Res., 115, D08203,
doi:10.1029/2009JD012637.
Ramanathan, V., and G. Carmichael (2008), Global and
regional climate changes due to black carbon, Nat.
Geosci., 1, 221–227, doi:10.1038/ngeo156.
Schulz, M., et al. (2006), Radiative forcing by aerosols as
derived from the AeroCom present‐day and pre‐industrial
simulations, Atmos. Chem. Phys., 6, 5225–5246,
doi:10.5194/acp-6-5225-2006.