Transitions
in the surface energy balance during the life cycle of a monsoon season
T N Krishnamurti摯瑬敳獩 and Mrinal K
Biswas
Department of Meteorology, The
Florida State University, Tallahassee,
FL 32306, USA.
∗e-mail: tnk@io.met.fsu.edu
Abstract: In this
observational/diagnostic study,we illustrate the time history
of some important parameters of the surface energy balance during the
life cycle of a single monsoon
season.This chronology of the surface energy balance portrays the di
fferential equilibrium
state from the preonset phase to the withdrawal phase.This includes an
analysis of the time history
of base variables such as soil moisture,ground temperature,cloud
cover,precipitation and
humidity.This is followed by an analysis of the components of the
surface energy balance where we
note subtle changes in the overall balances as we proceed from one
epoch of the monsoon to the
next.Of interest here is the transition
sequence:preonset,onset,break,revival,break,revival and
withdrawal during the year 2001.Computations are all illustrated for a
box over central India
where the coastal e ffects were small,data coverage was not sparse and
where the semi-arid land mass
changes drastically to a lush green area.This region exhibited large
changes in the components of
surface energy balance.The principal results pertain to what balances
the di fference among the
incoming short wave radiation (at the earth ’s surface)and the long
wave radiation exhibited by the
ground.That di fference is
balanced by a dominant sensible heat flux and the re flected short wave
radiation in the preonset stage.A sudden change in the Bowen ratio
going from >1to <1 is
noted soon after the onset of monsoon.Thereafter the latent heat flux
from the land surface takes an
important role and the sensible heat flux acquires a diminishing role.We
also examine the
subtle changes that occur in the components of surface energy balance
between the break and the active
phases.The break phases are seen to be quite di fferent from the
preonset phases.This study is
aimed to illustrate the major importance of moisture and clouds in the
radiative transfer
computations that are central to the surface energy balance during each
epoch.These sensitivities (of
moisture and clouds)have major consequences for weather and climate
forecasts.
Spatio-temporal
variability of summer monsoon rainfall over Orissa in relation to low pressure
systems
M Mohapatra 1 and U C Mohanty 2, ∗
1 India Meteorological Department,
Guwahati 781 015, Assam, India.
2 Centre for Atmospheric Sciences,
Indian Institute of Technology, Delhi, New Delhi 110 016, India.
∗e-mail: mohanty@cas.iitd.ernet.in
Abstract:The summer monsoon
rainfall over Orissa occurs mostly due to low pressure systems
(LPS)devel-oping over the Bay of Bengal and moving along the monsoon
trough.A study is hence undertaken to find out characteristic features
of the relationship between LPS over di fferent regions and rain- fall
over Orissa during the summer monsoon season (June –September).For this
purpose,rainfall and rainy days over 31 selected stations in Orissa and
LPS days over Orissa and adjoining land and sea regions during di
fferent monsoon months and the season as a whole over a period of 20
years (1980 –1999)are analysed.The principal objective of this study is
to find out the role of LPS on spatial and temporal variability of
summer monsoon rainfall over Orissa. The rainfall has been signi
ficantly less than normal over most parts of Orissa except the eastern
side of Eastern Ghats during July and hence during the season as a
whole due to a signi ficantly less number of LPS days over northwest Bay
in July over the period of 1980 –1999.The seasonal rainfall shows
higher interannual variation (increase in coe fficient of variation by
about 5%)during 1980 –1999 than that during 1901 –1990 over most parts
of Orissa except northeast Orissa.Most parts of Orissa,especially the
region extending from central part of coastal Orissa to western Orissa
(central zone)and western side of the Eastern Ghats get more seasonal
monsoon rainfall with the development and persistence of LPS over
northwest Bay and their subsequent movement and persistence over
Orissa.The north Orissa adjoining central zone also gets more seasonal
rainfall with development and persistence of LPS over northwest
Bay.While the seasonal rainfall over
the western side of the Eastern Ghats is adversely a ffected due to
increase in LPS days over west central Bay,Jharkhand and
Bangladesh,that over the eastern side of the Eastern Ghats is adversely
a ffected due to increase in LPS days over all the regions to the north
of Orissa.There are signi ficant decreasing trends in rainfall and
number of rainy days over some parts of southwest Orissa during June
and decreasing trends in rainy days over some parts of north interior
Orissa and central part of coastal Orissa during July over the period
of 1980 –1999.
Coupled
equations for transient water flow, heat flow, and deformation in hydrogeological systems
T N Narasimhan
Department of Materials Science and
Engineering, Department of Environmental Science,
Policy and Management, 210 Hearst
Memorial Mining Building,
University of California at Berkeley,
Berkeley, Ca 94720-1760, USA.
e-mail: tnnarasimhan@lbl.gov
Abstract:Hydrogeological
systems are earth systems in fluenced by water.Their behaviors are
governed by interacting processes,including flow of fluids,deformation of
porous materials,chemical reactions, and transport of matter and
energy.Here,coupling among three of these processes is considered: flow
of water,heat,and deformation,each of which is represented by a di
ffusion-type of partial di fferential equation.One side of the di
ffusion-type equation relates to motion of matter or energy, while the
other relates to temporal changes of state variables at a given
location.The coupling arises from processes that govern motion as well
as those that relate to change of state.In this work, attention is
devoted to coupling arising from changes in state.Partial derivatives
of equations of state constitute the capacitance terms of di
ffusion-type equations.Of the many partial derivatives that are
mathematically possible in physical systems characterized by several
variables,only a few are physically signi ficant.Because the state
variables are related to each other through an equation of state,the
partial derivatives must collectively satisfy a closure criterion.This
framework o ffers a systematic way of developing the coupled set of
equations that govern hydrogeological systems involving the flow of
water,heat,and deformation.Such systems are described in terms of
four variables,and the associated partial derivatives.The physical
import of these derivatives are discussed,followed by a description of
partial derivatives that are of practical interest.These partial
derivatives are then used as the basis to develop a set of coupled
equations.A brief discussion is presented on coupled equations from a
perspective of energy optimization.
Impact of
sea breeze on wind-seas o ff Goa, west coast of India
S Neetu 1 ∗,Satish Shetye 1 and P
Chandramohan 2
1 Physical Oceanography
Division,National Institute of Oceanography,Dona Paula,Goa 403
004,India.
2 Indomer Coastal Hydraulics
(P)Ltd,Ragamalika,Kumran Colony Main Road,Vadapalani,
Chennai 600 026,India.
∗e-mail:neetu@nio.org
Abstract:After withdrawal of
the Indian Summer Monsoon and until onset of the next
monsoon,i.e.,roughly during November –May,winds in the coastal regions
of India are dominated by sea breeze.It has an impact on the daily
cycle of the sea state near the coast.The impact is quite signi ficant
when large scale winds are weak.During one such event,1 –15 April
1997,a Datawell directional waverider buoy was deployed in 23 m water
depth o ffGoa,west coast of India.Twenty-minute averaged
spectra,collected once every three hours,show that the spectrum of
sea-breeze-related ‘wind-seas ’ peaked at 0 .23 ±0 .05 Hz.These
wind-seas were well separated from swells of frequencies less than 0.15
Hz.The TMA spectrum (Bouws et al 1985)matched the observed seas spectra
very well when the sea-breeze was active and the fetch corresponding to
equilibrium spectrum was found to be 77 ±43 km during such
occasions.We emphasize on the diurnal cycle of sea-breeze-related sea
o ffthe coast of Goa and write an equation for the energy of the seas as
a function of the local wind.
Auto-correlation
analysis of wave heights in
the Bay of Bengal
Abhijit Sarkar摯瑬敳獩 ,Jignesh Kshatriya摯瑬敳獩
∗and K Satheesan扵汬整
Meteorology &Oceanography
Group,Space Applications Centre,ISRO,Ahmedabad 380 015,India.
∗e-mail:sarkar −abhi2000@yahoo.com
∗∗e-mail:k −jignesh@ipdpg.gov.in
†e-mail:k −satheesan@redi ffmail.com
Abstract:Time series
observations of signi ficant wave heights in the Bay of Bengal were
subjected to auto-correlation analysis to determine temporal
variability scale.The analysis indicates an exponen-tial fall of
auto-correlation in the first few hours with a decorrelation time scale
of about six hours.A similar figure was found earlier for ocean surface
winds.The nature of variation of auto-correlation with time lags was
also found to be similar for winds and wave heights.
Correct
nomenclature for the Angadimogar pluton, Kerala, southwestern India
H MRajesh
Graduate School of Life and
Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan.
e-mail: rajesh.hm@gmail.com
Abstract:The proper
usage of modal composition and geochemical classi fication of granitoids
is discussed for assigning a proper nomenclature for the Angadimogar
pluton,Kerala,southwestern India.This discussion is mainly aimed at
addressing questions concerning the nomenclature of Angadimogar pluton
(syenite vs. granite).Modal composition and whole-rock XRD data clearly
show that the pluton exposed near Angadimogar is a quartz-syenite and
its geochemistry is typical of a ferroan,
metaluminous,alkali (A-type)granitoid.
Bedrock
gorges in the central mainland Kachchh: Implications for landscape evolution
M G Thakkar 1 ,B Goyal 1 ,A K Patidar
2 ,D M Maurya 2 and L S Chamyal 2, ∗
1 Department of Geology, R R Lalan
College, Bhuj, Kachchh 370 001, India.
2 Department of Geology, The Maharaja
Sayajirao University of Baroda, Vadodara 390 002, India.
∗e-mail: lschamyal@yahoo.com
Abstract:Kachchh possesses a
fault-controlled first-order topography and several geomorphic features
indica-tive of active tectonics.Though coseismic neotectonic activity
is believed to be the major factor in the evolution of the
landscape,detailed documentation and analysis of vital landscape
features like drainage characteristics,bedrock gorges and terraces are
lacking.The present study is a site-speci fic documentation of gorges
developed in the central part of the mainland Kachchh.We analyzed and
interpreted four gorges occurring on either side of Katrol Hill Fault
(KHF).The Khari river gorge is endowed with six levels of bedrock
terraces,some of which are studded with large potholes and
flutings.Since no active development of potholes is observed along the
rivers in the present day hyper-arid conditions,we infer an obvious
linkage of gorges to the humid phases,which provided high energy runo
fffor the formation of gorges and distinct bedrock terraces and
associated ero-
sional features.Development of gorges within the miliolites and
incision in the fluvial deposits to the south of the KHF indicates that
the gorges were formed during Early Holocene.However,ubi-quitous
occurrence of gorges along the streams to the south of KHF,the
uniformly N40 ◦Etrendof the gorges,their close association with
transverse faults and the short length of the exceptionally well
developed Khari river gorge in the low-relief rocky plain to the north
of KHF suggests an
important role of neotectonic movements.
Wave
velocities in a pre-stressed anisotropic elastic medium
M D Sharma 1 ∗and Neetu Garg 2
1 Department of
Mathematics,Kurukshetra University,Kurukshetra 136 119,India.
2 UIET,Kurukshetra
University,Kurukshetra 136 119,India.
∗e-mail:mohan −here@redi ffmail.com
Abstract:Modi fied
Christo ffel equations are derived for three-dimensional wave
propagation in a general anisotropic medium under initial stress.The
three roots of a cubic equation de fine the phase velocities of three
quasi-waves in the medium.Analytical expressions are used to calculate
the directional derivatives of phase velocities.These derivatives
are,further,used to calculate the group velocities and ray directions
of the three quasi-waves in a pre-stressed anisotropic medium.E ffect of
initial stress on wave propagation is observed through the deviations
in phase velocity,group velocity and ray direction for each of the
quasi-waves.The variations of these deviations with the phase direction
are plotted for a numerical model of general anisotropic medium with
triclinic/ monoclinic/orthorhombic symmetry.