Wind and Pressure Distribution on the Earth Surface for GSI, GG Gate, and CSIR Earth Science NET Exam

Mean Sea level pressure in July

Table of Contents

Distribution of Wind and Pressure over the surface of the earth

In subtropical region, the northeast trade winds and southeast trade winds prevail in the northern and southern hemisphere respectively. They are separated near the equator by a zone of prevailing calms known as ‘doldrums’.

However, the doldrums are frequently absent in one part or the other of the equatorial zone. Then the northeast trades and southeast trades meet directly at a surface of discontinuity on which strong rainsqualls may develop. The zone of doldrums is largely north of equator. Over some parts of the earth it even extends into southern hemisphere. Where the zone of doldrums is displaced far north from its symmetrical position at the equator, the southeast trade winds may reach into the northern hemisphere and get deflected into southwest winds under the influence of the coriolis force. Beyond the trade wind regions of each hemisphere are the zones of ‘prevailing westerlies’. These westerlies are better developed in the southern hemisphere than in the northern hemisphere. These zones of westerlies are the regions of the migrating cyclones and anticyclones. Poleward from the region of westerlies, beyond 65 to 75 latitude easterly winds with a component towards the equator prevail. The wind distribution as described is closely connected with the general pressure distribution.

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Mean Sea level pressure in january
Mean Sea level pressure in january
Mean Sea level pressure in July
Mean Sea level pressure in July

Near the equator, a zone of low pressure is found. It is followed in both hemispheres by zone of high pressure called ‘subtropical’ high-pressure belts. In summer hemisphere, these high-pressure belts do not extend continually around the earth but are interrupted over the continents since the land is hotter than the oceans. The central regions of the high-pressure belts have frequent calms. In the region of the westerlies even the mean pressure distribution is rather irregular because of the migrating pressure centers. On the whole, the pressure decreases here toward the pole. In the surface layers of the arctic and of the Antarctic zone, the pressure distribution is anticyclonic, because of the low temperature of the air in the surface layers. Since Greenland and Antarctica are not symmetrical with respect to the poles, the zones of the easterly winds in the polar regions are not symmetrical to the poles.


Effect of land and sea on the on the wind and pressure distribution

The unequal heating of water and land produces considerable modifications of the pressure and wind distribution. These deviations are more noticeable during the extreme months of January and July.

During July, the large continental mass of the northern hemisphere is much warmer than the surrounding oceans. Hence a low pressure is found over the continents, which interrupt the high-pressure belt.

The continental low is in direct connection with the equatorial low-pressure zone of doldrums. The southern hemisphere has winter in July so that here the land is colder than the water. But the disturbance of the pressure distribution is much less because of the smaller land area in the southern hemisphere. Over the continents, in the northern hemisphere during July, the northeast trade winds are absent. Instead, the southwest winds that are observed are continuation of the southeast trade winds of the southern hemisphere, which are deflected to southwest as they cross the equator.

The deflection of the southeast trades into the southwest monsoon is especially pronounced over India and the Indian Ocean. During January in the northern hemisphere, the continent is much colder than the adjoining oceans where a strong high is developed. On the south side of the continental anticyclone, the winds are northeasterly. The centers of low pressure over the oceans are considerably intensified during the winter so that the cyclonic activity is now at a maximum. On the north side of the continental anticyclone, the winds are westerly. Thus the belts of westerlies surround the northern hemisphere completely, but are displaced more northward over the continents. The southern hemisphere has its summer during January. Thus the pressure over the continents is now lower than over the adjoining oceans. As a result, the zone of doldrums with its low pressure shows a southward bulge over the continent. But the interruption of the southern subtropical highpressure belt by the continents during January is only slight.

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CSIR NET Exam: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

Exam Pattern: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES 

 PART APART BPART CTOTAL
Total questions205080150
Max No. of Questions to attempt15352575
Marks for each correct answer224200
Marks for each incorrect answer (Negative marking for part A & B is @ 25%, and part C is @ 33%)0.50.51.32–

The candidate is required to answer a maximum of 15, 35, and 25 questions from Part-A, Part-B, and Part-C, respectively. If more than the required number of questions are answered, only the first 15, 35, and 25 questions in Part A, Part B, and Part C, respectively, will be taken up for evaluation.

Below each question in Part A, Part B, and Part C, four alternatives or responses are given. Only one of these alternatives is the “correct” option to the question. The candidate has to find, for each question, the correct or the best answer.

Syllabus

EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

PAPER I (PART B)

  1. The Earth and the Solar System

    • Milky Way and the solar system.
    • Modern theories on the origin of the Earth and planetary bodies.
    • Earth’s orbital parameters, Kepler’s laws of planetary motion.
    • Geological Time Scale; space and time scales of processes in the solid Earth, atmosphere, and oceans.
    • Radioactive isotopes and their applications.
    • Meteorites: chemical composition and primary differentiation of the Earth.
    • Basic principles of stratigraphy.
    • Theories about the origin of life and fossil records.
    • Earth’s gravity, magnetic fields, and thermal structure: Geoid and spheroid concepts; Isostasy.

  2. Earth Materials, Surface Features, and Processes

    • Gross composition and physical properties of important minerals and rocks.
    • Properties and processes responsible for mineral concentrations.
    • Distribution of rocks and minerals in Earth’s units and India.
    • Physiography of the Earth; weathering, erosion, and soil formation.
    • Energy balance of Earth’s surface processes.
    • Physiographic features and river basins in India.

  3. Interior of the Earth, Deformation, and Tectonics

    • Basic concepts of seismology and Earth’s internal structure.
    • Physico-chemical and seismic properties of Earth’s interior.
    • Stress and strain concepts; rock deformation.
    • Folds, joints, and faults; causes and measurement of earthquakes.
    • Interplate and intraplate seismicity; paleomagnetism.
    • Sea-floor spreading and plate tectonics.

  4. Oceans and Atmosphere

    • Hypsography of continents and ocean floors: continental shelves, slopes, abyssal plains.
    • Physical and chemical properties of seawater; residence times of elements.
    • Ocean currents, waves, tides, thermohaline circulation, and conveyor belts.
    • Major water masses, biological productivity, and fluid motion.
    • Atmospheric structure and heat budget; greenhouse gases and global warming.
    • General circulation, monsoon systems, ENSO, cyclones, and local systems in India.
    • Marine and atmospheric pollution, ozone depletion.

  5. Environmental Earth Sciences

    • Properties of water and the hydrological cycle.
    • Energy resources: uses, degradation, alternatives, and management.
    • Ecology, biodiversity, and natural resource conservation.
    • Natural hazards and remote sensing applications.

PAPER I (PART C)

I. Geology

  1. Mineralogy and Petrology

    • Point group, space group, and lattice concepts.
    • Crystal field theory, mineralogical spectroscopy, and bonding in mineral structures.
    • Genesis, properties, and crystallization of magmas.
    • Metamorphic structures, textures, and thermobarometry.
    • Petrogenesis of Indian rock suites: Deccan Traps, charnockites, ophiolites, and more.

  2. Structural Geology and Geotectonics

    • Stress and strain analysis; Mohr circles.
    • Geometry and mechanics of folds, faults, and ductile shear zones.
    • Plate boundaries, mantle plumes, and Himalayan orogeny.

  3. Paleontology and Applications

    • Life origin theories, evolution models, and mass extinctions.
    • Applications of fossils in age determination, paleoecology, and paleogeography.
    • Micropaleontology in hydrocarbon exploration.

  4. Sedimentology and Stratigraphy

    • Classification of sediments and sedimentary rocks.
    • Sedimentary environments and basin evolution.
    • Stratigraphic principles, correlation methods, and sequence stratigraphy.
    • Phanerozoic stratigraphy of India.

  5. Marine Geology and Paleoceanography

    • Ocean floor morphology, ocean circulation, and thermohaline processes.
    • Factors influencing oceanic sediments and paleoceanographic reconstruction.

  6. Geochemistry

    • Atomic properties, periodic table, thermodynamics of reactions, and isotopes in geochronology.
    • Applications of stable isotopes in Earth processes.

  7. Economic Geology

    • Ore formation processes, mineral deposit studies, and petroleum geology.
    • Coal and unconventional energy resources.

  8. Precambrian Geology and Crustal Evolution

    • Evolution of Earth systems and Precambrian characteristics of India.
    • Precambrian–Cambrian boundary.

  9. Quaternary Geology

    • Quaternary stratigraphy, climate variability, and human evolution.
    • Dating methods and tectonic geomorphology.

  10. Applied Geology

  • Remote sensing and GIS.
  • Engineering properties of rocks; construction investigations.
  • Methods of mineral exploration and groundwater studies.

II. Physical Geography

  1. Geomorphology: Landform processes, DEM analysis, extraterrestrial geomorphology.
  2. Climatology: Radiation balance, wind systems, ENSO, and climate classification.
  3. Biogeography: Plant and animal associations, Indian biogeography, and conservation.
  4. Environmental Geography: Man-land relationships, hazards, and ecological balance.
  5. Geography of India: Physical geography, climatology, agriculture, and population characteristics.

III. Geophysics

  1. Signal Processing: Fourier transforms, filters, and signal analysis.
  2. Field Theory: Newtonian potential, Green’s theorem, and seismic wave propagation.
  3. Numerical Analysis and Inversion: Least squares, optimization, and pattern recognition.
  4. Gravity and Magnetic Methods: Data interpretation and anomaly analysis.
  5. Seismic Methods: Ray theory, reflection/refraction techniques, seismic stratigraphy.
  6. Well Logging: Techniques for lithology, porosity, and fluid saturation interpretation.

(IV) METEOROLOGY

1) Climatology

  • Same as under Geography.

2) Physical Meteorology

  • Thermal Structure of the Atmosphere and Its Composition.
  • Radiation:
    • Basic laws – Rayleigh and Mie scattering, multiple scattering.
    • Radiation from the sun, solar constant, effect of clouds, surface and planetary albedo.
    • Emission and absorption of terrestrial radiation, radiation windows, radiative transfer, Greenhouse effect, net radiation budget.
  • Thermodynamics of Dry and Moist Air:
    • Specific gas constant, adiabatic and isentropic processes, entropy and enthalpy.
    • Moisture variables, virtual temperature, Clausius–Clapeyron equation.
    • Adiabatic processes of moist air, thermodynamic diagrams.
  • Hydrostatic Equilibrium:
    • Hydrostatic equation, variation of pressure with height, geopotential, standard atmosphere, altimetry.
  • Vertical Stability of the Atmosphere:
    • Dry and moist air parcel and slice methods, tropical convection.
  • Atmospheric Optics:
    • Visibility and optical phenomena – rainbows, haloes, corona, mirage, etc.

3) Atmospheric Electricity

  • Fair weather electric field in the atmosphere and potential gradients.
  • Ionization in the atmosphere, electrical fields in thunderstorms.
  • Theories of thunderstorm electrification, structure of lightning flash, mechanisms of earth-atmospheric charge balance, and the role of thunderstorms.

4) Cloud Physics

  • Cloud classification, condensation nuclei, growth of cloud drops and ice-crystals.
  • Precipitation mechanisms: Bergeron–Findeisen process, coalescence process.
  • Precipitation of warm and mixed clouds, artificial precipitation, hail suppression, fog and cloud dissipation.
  • Radar observation of clouds and precipitation:
    • Radar equation, rain drop spectra, radar echoes of hailstorms, tornadoes, hurricanes, and rainfall measurements.

5) Dynamic Meteorology

  • Basic Equations and Fundamental Forces:
    • Pressure, gravity, centripetal and Coriolis forces.
    • Continuity and momentum equations (Cartesian and spherical coordinates).
    • Scale analysis, inertial flow, geostrophic and gradient winds, thermal wind.
    • Divergence and vertical motion, Rossby, Richardson, Reynolds, and Froude numbers.
  • Atmospheric Turbulence:
    • Mixing length theory, planetary boundary layer equations, Ekman layer, eddy transport of heat, moisture, and momentum.
  • Linear Perturbation Theory:
    • Internal and external gravity waves, inertia waves, gravity waves, Rossby waves, wave motion in the tropics, barotropic and baroclinic instabilities.
  • Atmospheric Energetics:
    • Kinetic, potential, and internal energies; conversion into kinetic energy; available potential energy.

6) Numerical Weather Prediction (NWP)

  • Computational instability, filtering of sound and gravity waves.
  • Filtered forecast equations, barotropic and baroclinic models.
  • Objective analysis, data assimilation techniques, satellite applications in NWP.

7) General Circulation and Climate Modelling

  • Observed zonally symmetric circulations, meridional circulation models.
  • General circulation modelling principles: grid-point and spectral GCMs.
  • Climate variability phenomena: ENSO, QBO, MJO, etc.
  • Ocean-atmosphere coupled models.

8) Synoptic Meteorology

  • Weather observations and transmission, synoptic charts.
  • Synoptic weather forecasting, prediction of weather elements, and hazardous weather phenomena.
  • Tropical Meteorology:
    • ITCZ, monsoons, tropical cyclones, jet streams.
  • Extra-Tropical Features:
    • Jet streams, extratropical cyclones, anticyclones.
  • Air masses and fronts: sources, classification, frontogenesis, and associated weather.

9) Aviation Meteorology

  • Meteorological role in aviation, weather hazards during takeoff, cruising, and landing.
  • In-flight hazards: icing, turbulence, visibility issues, gusts, wind shear, thunderstorms.

10) Satellite Meteorology

  • Polar orbiting and geostationary satellites.
  • Applications in identifying synoptic systems, cyclones, temperature estimation, rainfall prediction, and temperature/humidity soundings.

(V) OCEAN SCIENCES

1) Physical Oceanography

  • T-S diagrams, mixing processes, characteristics of water masses.
  • Wind-generated waves, shallow and deep-water wave dynamics.
  • Coastal processes: wave reflection, refraction, diffraction, littoral currents, rip currents, tsunami, and more.
  • Ocean Circulation:
    • Global conveyor belt circulation, Ekman’s theory, upwelling processes.

2) Chemical Oceanography

  • Composition of seawater, chemical exchanges, and classification of elements.
  • Element chemistry under special conditions (estuaries, vents, etc.).
  • Carbonate chemistry, biological pumps, and sedimentary deposit factors.

3) Geological Oceanography

  • Topics as listed under “Marine Geology & Paleoceanography.”

4) Biological Oceanography

  • Classification of marine environments and organisms.
  • Primary and secondary production, factors affecting biodiversity.
  • Human impacts on marine communities and climate change effects.

 

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