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Colored Rain on the West Coastal Region of India: Was it Due to a Dust Storm?

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Aerosol Science & Technology
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Satyanarayana Malladi
Satyanarayana Malladi
Veera Buthiran at Defence Research and Development Organisation
Veera Buthiran
D. Ramakrishna Rao
D. Ramakrishna Rao
D. Ramakrishna Rao
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Abstract and Figures

On 25 July 2001 some parts of Kerala in India on the west coast experienced the interesting phenomena called “colored rain.” Atmospheric dust particles had been detected on the previous day using a multiwavelength lidar system located at nearby Trivandrum (8.33°N, 77°E) on the west coast of India. This study concludes that the dust generated from desert areas of the west Asian countries was also one of the sources of the observed colored rain.
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Aerosol Science and Technology, 38:24–26, 2004
Copyright c
American Association for Aerosol Research
ISSN: 0278-6826 print / 1521-7388 online
DOI: 10.1080/02786820490247588
Colored Rain on the West Coastal Region of India: Was it
Due to a Dust Storm?
M. Satyanarayana, S. Veerabuthiran, D. Ramakrishna Rao,
and B. Presennakumar
Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India
On 25 July 2001 some parts of Kerala in India on the west coast
experienced the interesting phenomena called “colored rain.” At-
mospheric dust particles had been detected on the previous day us-
ing a multiwavelength lidar system located at nearby Trivandrum
(8.33◦N, 77◦E) on the west coast of India. This study concludes that
the dust generated from desert areas of the west Asian countries
was also one of the sources of the observed colored rain.
INTRODUCTION
It is clearly evident from the recent studies that the dust par-
ticles lifted into the atmosphere during dust storm activity form
a significant portion of the tropospheric aerosol. For example,
the Saharan mineral dust is believed to have been transported a
long way from its sources to tropical North Atlantic (Prospero
and Carlson 1979) and over various areas of the Mediterranean
(Dayon et al. 1991) and Arabian Seas. Similarly, soil particles
from the deserts of the Asian continent are frequently trans-
ported (Jaffe et al. 1999) over the eastern China Sea/Yellow
Sea, as well as over other Asian countries like India, Pakistan,
etc. Sometimes parts of the dust transported form a stratified
layer in the troposphere, typically in the 2–6 km region. Such
dust layers may impact the local climate and atmospheric envi-
ronment. In rare events, the dust storms may lead to “colored
rain” (Prospero et al. 1981). The rainwater droplets containing
mud observed over southern Spain on 30 July 2001 are a very
recent example of the change in environment due to the trans-
port of the dust particles (www.nrlmry.navy.mil/aerosol). Also,
there were reports indicating the presence of a “haze layer” in
the altitude region of 2–5 km in many of the tropical latitudes
(Ansmann et al. 2000). Such a haze layer was observed over the
Arabian Sea during the Indian Ocean Experiment (INDOEX),
Received 28 November 2001; accepted 25 June 2003.
Address correspondence to M. Satyanarayana, Space Physics Lab-
oratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, India.
E-mail: satyamalladi@vsnl.net
an international scientific study on aerosol conducted as a joint
program during 1996–1999. Ramanathan et al. (2001) made an
analysis of the haze layer and concluded that dust forms a con-
siderable portion of the observed aerosol layer. Here we report
a color rain event that occurred nearby our place in the west
coastal region of India and explain the plausible sources for the
observed phenomenon.
OBSERVATIONS
On 25 July 2001 many places in Kerala, India experienced
the colored rainwater droplets overnight and into the morning of
the next day. The red shower was accompanied by thunder and
lightning. Chemical analysis of the rainwater samples showed
the substantial concentration of carbon, silicon, calcium, magne-
sium, aluminium, iron, sodium, and potassium, and trace quanti-
ties (parts per million) of phosphorous and titanium. The reports
from the biological study conducted by some of the national
laboratories (Sampath et al. 2001) on the samples of the rain-
water collected also indicated the presence of a red-colored cell
structure.
A Multiwavelength lidar system is in regular use at a tropical
coastal station on the west coast of India at nearby Trivandrum
(8.33◦N, 77◦E). The main characteristics of lidar and the data
analysis procedure are described elsewhere (Satyanarayana et al.
2000). Lidar observations of aerosol characteristics in the lower
atmosphere from 600 m to 30 km on the night of 24 July 2001
revealed a dust layer at a height of about 4.5 km with a thick-
ness of 290 m. Figure 1 shows the aerosol extinction profiles
obtained on 24 July 2001, the day prior to the color rain event,
and also on 30 July 2001, five days after the event. In general,
aerosol extinction due to natural background aerosols decreases
with altitude. The unusual concentration of particles in any al-
titude region gets reflected as a layer with enhanced extinction
in the profile. The aerosol extinction coefficient profile derived
from the lidar data on 24 July 2001 clearly showed the enhanced
extinction values below 6 km, as seen in Figure 1. The peak value
of extinction coefficient at the layer was 7.06E-5 m−1, centered
24
COLORED RAIN ON THE WEST COASTAL REGION OF INDIA 25
Figure 1. Aerosol extinction coefficient obtained on 24 and
30 July 2001 using lidar (532 nm) in the lower troposphere.
around 4.5 km with a thickness of 290 m. This continuous high
extinction coefficient was attributed to dust throughout the at-
mospheric column. Although the aerosol extinction values were
lower on 30 July than on 24 July, a dust layer was also ob-
served on 30 July at a slightly lower altitude with a lower peak
extinction coefficient value of 8.06E-6 m−1and thickness of
270 m. Also, the Total Ozone Mapping Spectrometer (TOMS)
aerosol index images for 17 and 19 July 2001 confirmed the
dust storm activity over Pakistan and the northwestern parts of
India.
In order to discover the plausible sources of this aerosol layer
observed in the small region centered around 4.5 km, we had
computed the back trajectory during that period. Figure 2 shows
the trajectories at 1.0, 3.0, and 4.5 km levels for 9 days. The
back trajectories started from Afghan region at 12:00 h UTC on
16 July 2001 ended at Trivandrum on 24 July 2001 at 1500 h
UTC. The trajectory, which starts northwest of Trivandrum (◦),
describes the air flow at about 4.5 km height level; the trajectory
west of Trivandrum () indicates air flow at about 3.0 km height
level; and the trajectory southeast of Trivandrum (∇) indicates
air flow at about 1.0 km height level. The main transport of dust is
between 4.5 km and 6.0 km, and this is the region where the dust
layer with prominent peak was detected by the lidar on 24 July
2001. Study of the air mass trajectory clearly shows that the air
mass starts from Afghanistan and travels through Pakistan and
northwestern parts of India. After that, it turns northwesterly
over Arabian Sea and arrives at the lidar site. The trajectories
for the air mass at 3.0 km and 1.0 km indicated that they were
Figure 2. Nine-day air mass back trajectory analysis ending at
1000 m, 3000 m, and 4500 m over Trivandrum on 24 July 2001.
Results are given for the arrival time at 1500 UTC. The arrival
heights above the field site are given in the plot. The time step
between individual symbols is 12 h. Star denotes the lidar site,
Trivandrum.
from African countries and Indian Ocean region, respectively. It
takes about 5–9 days for the dust-laden air to travel from the dust
activity region to the Kerala coast. Almost at the same time mon-
soon activity intensified off the Kerala coast. The phenomenon
of color rain was a blend of these meteorological movements.
During the last week of July 2001 when color rain showered on
the landscape in the region, the wind over the area close to and
west of Kerala was from the northwest. The week, preceding the
fresh surge of monsoon, was practically dry over Kerala when
dust sedimentation is intense. Similarly, there was an intense
dust storm activity in the dust bowl during the period before
Kerala experienced this phenomenon. The dust settles almost at
the same height, where clouds are formed. A rare combination of
many meteorological factors might have resulted in the rain with
red color containing all the ingredients of the dust. We conclude
from our lidar observations and air mass back trajectories shown
above that the transport of aerosols/dust from far off places is
one of the sources of the observed color rain around Trivandrum
in Kerala.
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Studies in the Atmosphere, Asian J. Phys. 18:191–195.
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... The absolute value of the aerosol extinction coefficient obtained from the lidar backscattered signal depends on the assumed value of LR [18], [36], [37] have used the actual lidar data obtained from the lidar experiments conducted using the multi-wavelength lidar system at the Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India. In this study, the reference boundary value ) ( m t r α , is taken using the aerosol model generated from various ground based experiments including a multi-wavelength solar radiometer for a period of three years at the Trivandrum station relating to the specific season of the year under various scientific programs [22], A typical LR value of 20 sr (at the laser wavelength of 532 nm) corresponding to marine aerosols pertaining to the Trivandrum station is assumed in this study [28]. ) It can be seen fromFig. 1 ...
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Article
  • Feb 1981
The arid and desert regions of North Africa are a prolific source of atmospheric dust. This dust is, for example, responsible for the `red snows' reported in the Alps and Pyrenees1 and for dust falls further north in Europe2-6, but these phenomena are infrequent and sporadic. By contrast, the transport of mineral dust into the tropical North Atlantic is common and often produces a widespread dense haze7. Investigations in the past 15 yr8-11 have shown that, in the summer months12,13, the distribution of dust is related to macro and micro-meteorological circumstances, that the dust often reaches altitudes of 5-7 km and that it may be spread over several hundreds of kilometres in latitude and extend to the Caribbean Sea and the south-east United States. We report here the results from an aerosol sampling station at Cayenne, French Guiana, which indicate that large quantities of soil dust are being carried out of North Africa and across the Atlantic during the winter months as well but at this time of year the transport is primarily to South America.
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Colored Rain: A Report on the Phenomenon, CESS-PR-114-2001
  • Jan 2001
  • S Sampath
  • T K Abraham
  • V Sasikumar
  • C N Mohanan
Sampath, S., Abraham, T. K., Sasikumar, V., and Mohanan, C. N. (2001). Colored Rain: A Report on the Phenomenon, CESS-PR-114-2001, Centre for Earth Science Studies, Trivandrum (www.cessind.org).