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Drastic variation in the surface boundary layer parameters over
Cochin during the annular solar eclipse: Analysis using sonic
anemometer data
P.R. Jayakrishnan
n
, C.A. Babu, P. Sivaprasad
Department of Atmospheric Sciences, Cochin University of Science and Technology, Cochin682 016, India
article info
Article history:
Received 13 May 2012
Received in revised form
11 December 2012
Accepted 23 December 2012
Available online 14 January 2013
Keywords:
Annular solar eclipse
Surface boundary layer
Sonic anemometer
abstract
Atmospheric surface boundary layer parameters vary anomalously in response to the occurrence of
annular solar eclipse on 15th January 2010 over Cochin. It was the longest annular solar eclipse
occurred over South India with high intensity. As it occurred during the noon hours, it is considered to
be much more significant because of its effects in all the regions of atmosphere including ionosphere.
Since the insolation is the main driving factor responsible for the anomalous changes occurred in the
surface layer due to annular solar eclipse, occurred on 15th January 2010, that played very important
role in understanding dynamics of the atmosphere during the eclipse period because of its coincidence
with the noon time. The Sonic anemometer is able to give data of zonal, meridional and vertical wind as
well as the air temperature at a temporal re solution of 1 s. Different surface boundary layer parameters
and turbulent fluxes were computed by the application of eddy correlation technique using the high
resolution station data. The surface boundary layer parameters that are computed using the sonic
anemometer data during the period are momentum flux, sensible heat flux, turbulent kinetic energy,
frictional velocity (u
*
), variance of temperature, variances of u, v and w wind. In order to compare the
results, a control run has been done using the data of previous day as well as next day. It is noted that
over the specified time period of annular solar eclipse, all the above stated surface boundary layer
parameters vary anomalously when compared with the control run. From the observations we could
note that mom entum flux was 0.1 Nm
2
instead of the mean value 0.2 Nm
-2
when there wa s eclipse.
Sensible heat flux anomalously decreases to 50 Nm
2
instead of the mean value 200 Nm
2
at the time
of solar eclipse . The turbulent kinetic energy decreases to 0.2 m
2
s
2
from the mean value 1 m
2
s
2
. The
frictional velocity value decreases to 0.05 ms
1
instead of the mean value 0.2 ms
1
. The present study
aimed at understanding the dynamics of surface layer in re sponse to the annular solar eclipse over a
tropical coastal station, occurred during the noon hours. Key words: annular solar eclipse, surface
boundary layer, sonic anemometer
& 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Solar eclipse is a celestial phenomenon in which the moon
passes between the Sun and Earth, and then it makes a shadow on
the Earth, which can be viewed as a blocking of sunlight partially
or fully. When the Sun is fully covered by the Moon it is known as
total solar eclipse and when it is partially covered it is known as
partial solar eclipse. It could occur at any time of the day. During
the day time, due to the solar heating the Earth’s surface gets
heated up and thermals begin to rise. There is a regular diurnal
variation for every surface atmospheric boundary layer (ABL)
parameters. The maximum air temperature is noted at a time of
about 14.00 IST over the tropical stations. Corresponding to this
maximum in temperature most of the surface ABL parameters are
found to be maximum during the time. The total solar eclipse is a
situation in which there is a blocking of solar radiation for a small
interval of time. So the changes that occur for surface ABL is
purely a micro meteorological phenomenon since the process has
the time scale of the order of a few hours (Stull ,1988). It is very
interesting to note how these surface boundary layer parameters
vary in response to the celestial phenomenon such as solar
eclipse.
Several studies were carried out over different parts of India to
quantify the changes in the surface atmospheric boundary layer
in response to the total annular solar eclipse of 15th January 2010.
Venkat Ratnam et al. (2010) analyzed the changes in lower
atmospheric boundary layer over the site Gadanki using a set of
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/jastp
Journal of Atmospheric and Solar-Terrestrial Physics
1364-6826/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jastp.2012.12.019
n
Corresponding author. Tel.: þ91 9496026547; fax: þ91 484 2353662.
E-mail addresses: prjayakrishnan@gmail.com, jkprdas@gmail.com
(P.R. Jayakrishnan).
Journal of Atmospheric and Solar-Terrestrial Physics 94 (2013) 49–53
Author's personal copy
instruments including automatic weather station, Doppler SODAR
and GPS sonde. They found that the effect of soil temperature is
seen clearly up to 20 cm depth and at all the levels up to 15 m.
They could obtain strong eclipse induced variations in meteor-
ological parameters of the surface layer over Gadanki.
Subrahamanyam et al. (2010) studied the impact of 15th January
2010 solar eclipse over Thumba, a south Indian coastal station.
They investigated the variations in surface ABL using AWS, sonic
anemometer and GPS radiosonde. Associated with the decrease in
radiation intensity, they could obtain significant changes in
boundary layer parameters as well as thermodynamic para-
meters. Bala Subrahamanyam and Anurose (2011) analyzed the
impacts on sea/land breeze circulation characteristics over
Thumba in response to the annular eclipse of January 15, 2010.
They observed that the vertical thickness of the sea breeze cell
was confined to 300 m on the eclipse day whereas it was
extending to about 610 m on the control run day.
Muraleedharan et al. (2011) also studied the impact of annular
solar eclipse on the meteorological parameters over Goa. They
observed a strong inversion at 13 km and an abnormal warming
in the upper troposphere noticed on the eclipse day.
The Space physics Laboratory (SPL), Thiruvananthapuram
carried out extensive and collocated experiments over different
regions of the atmosphere in the field experiment named ‘Surya-
grahan-2010’, which was organized by Vikram Sarabhai Space
Centre (VSSC). The outcome of the field campaign has been
published as proceedings of the National Workshop: Results on
Solar Eclipse (NaWRoSE, 2011). It discusses the effects of annular
solar eclipse over different regions of the atmosphere such as
boundary layer, troposphere, stratosphere and ionosphere.
The solar eclipse induced variations have been extensively
analyzed over different parts of the globe by several researchers
(Sethu Raman, 1982; Aplin and Harrison, 2003; Foken et al., 2001;
Sethu raman et al., 1990; Altadilla et al., 2001; Afraimovich et al.,
2002; Founda et al., 2007; Stoev et al., 2008). They reported that
the boundary layer responded to the eclipse induced changes in
surface layer rapidly. The variations are found to be in association
with the sharp drop in the direct solar radiation. In this study we
investigate the micro meteorological variations of surface layer
parameters during the occurrence of the annular solar eclipse of
15th January 2010, over the coastal station Cochin (10
1
02’41’’ N,
76
1
19’34’’ E, 38 m ASL).
2. Data and methodology
The sonic anemometer USA-1 (make: METEK, GmbH,
Germany) was installed at Kalamassery (10102
0
41
00
N, 76119
0
34
00
E, 38 m ASL) in Cochin University campus in January, 2008.
It provides zonal, meridional and vertical components of wind
as well as air temperature at a temporal resolution of one second.
With the availability of this fast response instrument installed at a
height of 7 m above ground level we are able to get continuous
observation of wind and temperature at the station. The raw data
sets were archived after quality check. The different statistical
parameters and surface boundary layer parameters as well as
surface fluxes were computed using the eddy correlation method
as described in Arya (2001). The parameters investigated in this
study are momentum flux, sensible heat flux, turbulent kinetic
energy, frictional velocity, and variance of u, v, w, t.
Using the Eddy correlation method different parameters are
computed using the following formulae:
MomentumFlux ¼
r
u
n
2
ðNm
2
Þð1Þ
SensibleHeatFlux ¼
r
C
p
u
n
y
n
ðWm
2
Þð2Þ
where frictional velocity u
n
¼ðu
0
w
02
þv
0
w
02
Þ
1=4
ð3Þ
y
n
¼w
0
y
0
=u
n
ð4Þ
Turbulent kinetic energy ðTKEÞ¼1=2ðu
02
þv
02
þw
02
Þðm
2
s
2
Þð5Þ
where
r
is the air density which is taken as 1.2 kg m
3
, C
p
is the
specific heat capacity of dry air at constant pressure which can be
taken as 1004 J K
1
kg
1
,u
0
,v
0
and w
0
are the fluctuations of wind
components from the mean, as described in Stull (1988).
The different variances can be computed as
Variance u ¼
u
2
ð6Þ
Variance v ¼
v
2
ð7Þ
Variance w ¼
w
2
ð8Þ
Variance t ¼
t
2
ð9Þ
For the computation of fluxes and statistical parameters the
averaging time taken is 10 min, since it is suitable for the eddy
correlation method (Stull, 1988).
2.1. Details of annular solar eclipse of 15th January 2010
Annular solar eclipse took place over India on 15th January
2010. The eclipse had a magnitude of 0.9190 and it was the
longest solar eclipse with a duration of about 11 min and 7.8 s.
The other peculiarity of the eclipse is that its peak period was in
the noon hours, when we receive maximum insolation from the
sun. The time of the occurrence of the eclipse is from 11.25 AM to
15.15 PM IST. This solar eclipse was also visible in Singapore,
Dubai, Qatar, Bahrain, Kuwait, Oman, Pakistan, Sri Lanka, Malay-
sia, Africa, Europe, and parts of China. In India, the path of eclipse
was through Palk straight among South Kerala, South Tamil Nadu
and North Sri Lanka.
3. Results and discussions
In this paper we present the anomalous variation of different
surface boundary layer parameters over the coastal station,
Cochin in association with the occurrence of annular solar eclipse.
The parameters studied are momentum flux, sensible heat flux,
frictional velocity, turbulent kinetic energy and variances of u, v,
w, t. For the sake of comparison, a control run was made for all the
parameters in the days before and after the solar eclipse day. The
control run days were taken as 14th January 2010, which was
the day prior to solar eclipse and 16th January 2010, which
was the day after solar eclipse over Cochin. In the discussion
part, the figure of the control run for 16th January 2010 was taken
into consideration for comparison. The variation of surface
boundary layer parameters associated with the annular solar
eclipse is summarized below.
Fig. 1 gives the diurnal variation of momentum flux and sensible
heat flux on the control run day, 16th January 2010 as well as on the
annular eclipse day. On the eclipse day ie. on 15th January 2010, the
momentum flux shows anomalous decrease in the noon hours. It
decreases up to 0.01 Nm
2
atthetime14:00IST(Fig. 1(a)). This
anomalous decrease is attributed to the occurrence of annular solar
eclipse. Due to the solar radiation cut off for a short period,
boundary layer wind and temperature vary in a micro scale of the
order of a few hours. So this is typically a micro meteorological
phenomenon. Fig. 1(b) shows the diurnal variation of momentum
flux on the control run day, 16th January 2010. In response to the
evolution of convective boundary layer, momentum flux also shows
a diurnal maximum and minimum. The maximum flux of 0.4 Nm
2
P.R. Jayakrishnan et al. / Journal of Atmospheric and Solar-Terrestrial Physics 94 (2013) 49–5350
Author's personal copy
occurred at 16:00 IST. Mitsuta (1958) presented the results of direct
measurements of momentum flux in the surface ABL using sonic
anemometer. In his experiment at a height of 2 m level he could
obtain a momentum flux value of 0.53 Nm
2
, which agrees with the
flux value in our analysis. Chehbouni et al. (2000) obtained a
momentum flux value of 0.6 Nm
2
over a grassland patch using
scintillometer based and eddy correlation based experiments that
also agree with our observations. In the study reported by Bala
Subrahamanyam et al. (2011), the impact of annular solar eclipse on
the boundary layer over Thumba is discussed. They could observe
significant reduction in momentum flux from 0.4 Nm
2
on the
control run day to 0.05 Nm
2
on the solar eclipse day. This agrees
with our observations.
Fig. 1(d) gives the diurnal variation of sensible heat flux on the
control run day 16th January 2010. The sensible heat flux has a
maximum value of 300 Wm
2
during the noon hours at the time
15:00 IST. On the solar eclipse day from Fig. 1(c), the sensible heat
flux decreases anomalously in the noon hours with minimum
value of 10 Wm
2
at the time 14:00 IST. This anomalous
decrease is attributed to the annular solar eclipse occurred in
the noon hours. In the next control run day i.e 16th January
(figure not attached), we could observe normal sensible heat flux
values in the noon hours with value 400 Wm
2
. Chehbouni et al.
(2000) got a sensible heat flux value of 300 Wm
2
based on the
eddy correlation method which agrees with the observations we
got on the control run day. Bala Subrahamanyam et al. (2011)
observed a reduction of sensible heat from 300 Wm
2
to 20
Wm
2
during the annular solar eclipse period. This also agrees
well with our observations. Krishnan et al. (2004) obtained the
value of sensible heat flux as 10 Wm
2
during the occurrence
of solar eclipse of 11th August 1999 over a semi arid region
Ahammadabad.
Diurnal variation of turbulent kinetic energy on the control run
day 16th January is shown in Fig. 2(b). Associated with the
convective boundary layer growth, T.K.E also increases and
becomes a maximum in the noon hours. The maximum value is
1m
2
s
2
at about 15:00 IST. On the day of solar eclipse, between
time 11:30 to 15:00 IST the T.K.E sharply decreases to very low
value of about 0.1 m
2
s
2
and approaches zero (Fig. 2(a)). This
sharp decrease is due to the suppression of turbulence due to the
cut off radiation in the noon hours and this is in response to the
annular solar eclipse. In the analysis by Krishnan et al. (2004) the
obtained T.K.E during solar eclipse was 0.2 m
2
s
2
and this agrees
well with our results. Rajeev et al. (2011) estimated the reduction
in T.K.E during the eclipse period as 0.025 m
2
s
2
, while frictional
velocity decreased to as low as 0.05 ms
1
, which are attributed to
the decrease in turbulence fluctuations of wind components
during solar eclipse.
The diurnal variation of frictional velocity on the control run
day (16th January 2010) is given in Fig. 2(d). As evidenced from
the figure, during the noon hours maximum variation for u
n
takes
place and it has a maximum value of 0.5 ms
1
at the time 15:00
IST in response to the convection. But on the solar eclipse day, u
n
decreases and reaches a minimum of 0.1 ms
1
at the time 13:00
IST, due to the influence of annular solar eclipse (Fig. 2 (c)). After
the solar eclipse it recovers to normal values. On the control run
day 14th January 2010, u
n
again shows normal diurnal behavior
with maximum value 0.5 ms
1
(figure not attached). In the work
by Krishnan et al. (2004), they got a frictional velocity of 0.3 ms
1
and it is found to decrease to 0.05 ms
1
during the eclipse period.
Namboodiri et al. (2011) observed a reduction of frictional
velocity value from 0.3 ms
1
to 0.1 ms
1
which agrees with our
observation. Also Rajeev et al. (2011) estimated the frictional
velocity using sonic anemometer during annular solar eclipse
found to be 0.05 ms
1
from 0.3 ms
1
. These previous studies
were compared with our results and obtained good matching of
the observations.
The variances u, v, w and t are shown in the Figs. 3 and 4 on the
control run day 16th January 2010 as well as on the annular solar
eclipse day. As evident from the figure, maximum value for all the
variances occur in the noon hours corresponding to time 17: 00
IST. The variances in u and v have maximum value 1 m
2
s
2
at the
time 17:00 IST, variance w has maximum value of 0.5 m
2
s
2
at
the time 15:00 IST and variance t shows maximum value of
0.8 m
2
s
2
at the time 15:00 IST on the control run day 16th
January. Corresponding to the annular solar eclipse, there is sharp
decrease of variances as evidenced by the figure. Variances u and
v show minimum value of about 0.1 m
2
s
2
at the time 14:00 IST
due to the solar eclipse. Variance w has minimum value of
0.1 m
2
s
2
at the time 14:00 IST and variance t decreases to value
0.1 K
2
s
2
at the time 14:00 IST in response to the solar eclipse.
The statistical parameters such as variances decrease due to the
Fig. 1. Diurnal variation of surface boundary layer parameters on the annular
eclipse day as well as on the control run day (a) Momentum Flux on eclipse day
(b) Momentum flux on control run day (c) Sensible heat flux on eclipse day and
(d) Sensible heat flux on control run day. The portions inside the dotted lines
indicate the time period of solar eclipse.
Fig. 2. Diurnal variation of surface ABL parameters on eclipse day as well as the
control run day (a) Turbulent Kinetic Energy on eclipse day (b) Turbulent kinetic
energy on control run day (c) Frictional velocity on eclipse day and (d) Frictional
velocity on control run day. The portions inside the dotted lines indicate the time
period of solar eclipse.
P.R. Jayakrishnan et al. / Journal of Atmospheric and Solar-Terrestrial Physics 94 (2013) 49–53 51
Author's personal copy
fact that, wind and temperature fluctuations are found to
decrease due to the sudden ceasing of solar irradiance. This is
indeed reflected in the decreasing of variances of wind and
temperature.
4. Conclusions
It is observed that the surface boundary layer parameters are
varying sharply in response to the solar eclipse, which is attributed to
the depletion of the solar radiation for a short interval of time. This
situation is similar to that of total overcasting of cloud and decrease in
radiation. Since solar energy is the primary source of energy for
atmospheric boundary layer, its cut off for a short period has
significant effect on surface ABL parameters. On the eclipse day,
momentum flux decrease s anomalously from 0.5 Nm
2
to
0.01 Nm
2
. Sensible heat flux decreases from its normal value
300 Wm
2
to -10 Wm
2
due to the effect of solar eclipse. Turbulent
kinetic energy also decreases sharply from its normal value 1 m
2
s
2
to 0.1 m
2
s
2
on the eclipse day. Frictional velocity has a normal value
0.5 m s
1
in the control run day and it decreases anomalously to
0.1 m s
1
. The corresponding variances of u, v, w and t are also found
to decrease anomalously. Generally during noon hours, the convective
boundary layer grows in respo nse to the convective thermals. Due to
the occurrence of annular solar eclipse, this growth of convective
boundary layer is blocked and hence the anomalous changes in
surface ABL occur.
Acknowledgments
The first author acknowledges the fellowship received from
CSIR, New Delhi and the third author acknowledges the fellow-
ship received from UGC New Delhi during the period of study. The
authors acknowledge CUSAT for the facilities and infra structure
provided by the Department of Atmospheric Sciences.
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Fig. 3. Diurnal variation of variances on the annular solar eclipse day as well as on
the control run day (a) Variance U on eclipse day (b) Variance U on control run day
(c) Variance V on solar eclipse day and (d) Variance V on control run day. The
portions inside the dotted lines indicate the time period of solar eclipse.
Fig. 4. Diurnal variation of variances on the annular eclipse day as well as on the
control run day (a) Variance W on eclipse day (b) Variance W on control run day
(c) Variance T on solar eclipse day (d) Variance T on control run day. The portions
inside the dotted lines indicate the time period of solar eclipse.
P.R. Jayakrishnan et al. / Journal of Atmospheric and Solar-Terrestrial Physics 94 (2013) 49–5352
