Global Energy and Water Cycle, and its Budgets

Kooiti MASUDA
Frontier Research System for Global Change
Yokohama 236-0001, Japan

Advanced Seminar
on Hydrology, Meteorology, Climatology and Water Resources Studies
for Thailand

1 November 2002

at Chulalongkorn Univeristy, Bangkok, Thailand

U.S. Committee for GARP (1975): "Understanding Climate Change"
Note: English words in this figure are not faithful to the original.

• In this 1975 version, Climate System = Atmosphere + Ocean + Ice
  • interacting each other by exchanging energy, water and/or momentum.
• Later variants usually include "Land (surface)" and/or "Biosphere".
  • This "Land" is as deep as they interact with Atmosphere, Ocean and/or Ice
    • by effectively exchanging energy, water and/or momentum.

• "Climate system" is the middle one among the three "spheres" shown.
• It is a thin layer (< 100 km) compared with the radius of the earth (6370 km).

"Climate system" (including ourselves) is a physical system,
though we cannot predict its behavior with physics alone.

• Law(s) of conservation
  • ... of mass
    • of mass of water (H₂O, 3 phases together) ... good approximation
    • of mass of air ... good approximation except that water vapor can change
  • ... of energy (= first law of thermodynamics)
  • ... of momentum (= Newton's equation of motion)
  • (Law of increase of entropy (= second law of thermodynamics))
• Meaning of "conservation of X"
  • In an isolated system, the total of X do not change with time.
    • dX/dt = 0
  • In an open system, the change of X is equal to the net inflow of X.
    • dX/dt = (inflow of X) - (outflow of X)
  • If a steady state can be assumed,
    • 0 = (inflow of X) - (outflow of X)
• What can be gained by budget analysis?
  • Estimation of unknown component of balance
  • Assessment of accuracy if all components are measured

• Years are expressed in Thai Buddist Era in (only) this page.
• (Seminal team research activities in 2490s, e.g. Budyko, Starr, London)
• 2500-2501: International Geophysical Year
  • Enhanced observations of the earth (e.g. geomagnetism)
  • Compilation of meteorological data -> water balance (Peixoto, 2513)
  • Sharing data through "World Data Centers"
  • First artificial satellite (Soviet's Sputnik -- not for observation)
    • Satellite for observation -> energy balance (Vonder Haar & Suomi, 2514)
• Global Atmospheric Research Programme
  • Understanding of the general circulation of the atmosphere
  • Medium-range (ca. week) weather forecasting
  • Non-military use of satellites
    • Geostationary Meteorological Satellite (Japan) started obs. in 2521
  • 2521-2522: First GARP Global Experiment and MONsoon EXperiment
    • Production of non-real-time data set for 1-year period
    • Application to energy and water budgets (e.g. Masuda, 2531)
• World Climate Research Programme
  • Global Energy and Water cycle EXperiment
    • GEWEX Asian Monsoon Experiment
    • 2541: GAME Intensive Observing Period

Exchange of mass at the top of the atmosphere can be ignored

<==	Water vapor transport by the atmosphere	<==
|			^
|			|
precipitation			evaporation
v			|
==>	Runoff and net water transport by ocean	==>

Exchange of mass at the bottom of the ocean/groundwater can be ignored

Storage terms [kg / m²] or [mm] (assuming standard density of liquid water)

• W: atmospheric Water vapor content ("precipitatble water")
• S: terrestrial water Storage (surface water + snow + soil moisture + groundwater)

Flux terms [kg /(m² s)] or [mm / s] (usually [mm/day], [mm/year] etc. are used)

• C: Convergence of water vapor transport; P: Precipitation;
• E: Evaporation; R: Runoff (in ocean, divergence of net freshwater transport)

For steady state (long-term mean), C = R. For global domain, C = R = 0.

1 degree latitude/longitude grids, following
Total Runoff Integrated Pathways (Oki and Sud, 1998)

• x: Runoff (river discharge at station / drainage area of the station)
• y: moisture Convergence (European Centre for Medium-range Weather Forecasts Re-Analysis for 15-year period, processed by A. Yatagai [RIHN Kyoto])

Chao Phraya, Mekong and Irrawaddy are circled.
In the following analysis, C is adjusted so that it matches R in long-term average.

1979-1993, with ERA15
Mekong ---------- Chang Jiang (Yangtze) ---------- Huang He (Yellow)


(S is shown as values relative to its minimum in the annual cycle.)
Tropics and temperate East Asia: S takes maximum at the end of rainy season.

1979-1993, with ERA15
Huang He (Yellow) ---------- Amur (Heilong Jiang) ---------- Lena


(S is shown as values relative to its minimum in the annual cycle.)
Temperate East Asia: S takes maximum at the end of rainy season.
Cold region: S takes maximum at the snowmelt season.

1979-1993, with ERA15
Chang Jiang (Yangtze) ---------- Mississippi ---------- Parana (La Plata)


(S is shown as values relative to its minimum in the annual cycle.)
Temperate East Asia & South America: S takes maximum at the end of rainy season
Temperate North America: S takes maximum in spring.

1979-1993, with ERA15

• Land: S for 1979-1993 with ERA15 and river runoff data
• Ocean: sea level from satellite altimeter, density from ship obs. temp. & salinity
• Vapor: NASA VAPor data set, combination of satellite and sonde obs.

• Types of heat transfer
  • Conduction: transfer of molecular energy without movement of mass
  • Convection (broader sense): transfer of energy with movement of mass
  • Radiation: transfer of mass by electromagnetic waves
• Energy contained by (unit mass of) air
  • Potential energy ... g z [g: acceleration of gravity; z: height]
  • Internal energy
    • "Sensible" part ... C_v T [C_v: specific heat; T: absolute temperature]
    • Latent part ... L q [L: latent heat per mass of water; q: specific humidity]
  • Kinetic energy ... (1/2) v² [v: wind speed] (relatively small)
• Exchange of energy at the top of the atmosphere ... radiation only
  • Solar (shortwave) radiation ... visible and near-infra-red
  • Terrestrial (longwave) radiation ... infra-red
• Exchange of energy at the (land/sea) surface ... Rnet = H + L E + G
  • Rnet(d): Net Radiation (solar and terrestrial)
  • H(u): Sensible Heat flux to atmosphere (conduction, small-scale convection)
  • L E(u): Latent heat flux of evaporation (E: mass flux of evaporation)
  • G(d): Net heat flux below surface (conduction, small-scale convection)
    • (u) upward positive; (d) downward positive

Storage terms [J / m²]

• Ea: atmospheric energy storage; Eo: oceanic or terrestrial energy storage

Flux terms [J /(m² s)] or [W / m²]

• Rnet,top: net radiation at the top; div Fa: div. of atmospheric energy transport;
• div Fo: div. of oceanic energy transport;
• G: net downward energy flux at the surface

For steady state (long-term mean), G = 0. For global domain, div Fa = div Fo = 0.

Annual and zonal average
based on satellite observations (ERBE S4 NFOV) Feb. 1985 - Apr. 1989

Feb. 1985 - Apr. 1989 (period of ERBE S4 NFOV data)

• Radiation at the top of atmosphere: satellite observation (ERBE S4 NFOV)
• Atmosphere: "Reanalysis" products (two versions of U.S. NCEP)
• Ocean: residual

cf. Trenberth & Caron 2001, J. Climate; Masuda 1988 Tellus

Feb. 1985 - Apr. 1989, "Reanalysis" products (two versions of NCEP)

• Tropics: meridional-vertical overturning (quantitatively still large uncertainty)
  • Water vapor (mainly near the surface) toward equator
  • "Dry energy" (mainly about 15 km height) away from equator
• Middle latitudes: both water vapor and "dry energy" toward poles

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