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Geosciences LibreTexts

B Constants and Conversion Factors

  • Page ID
    10995
  • B.3. Earth Characteristics  

    1° latitude = 111 km = 60 nautical miles (nm) [Caution: This relationship does NOT hold for degrees longitude.]

    a = 149.598 Gm = semi-major axis of Earth orbit

    A = 0.306 = Bond albedo (NASA 2015)

    A = 0.367 = visual geometric albedo (NASA 2015)

    b = 149.090 Gm = semi-minor axis of Earth orbit

    d = 149.5978707 Gm = average sun-Earth distance = 1 Astronomical Unit (AU) (NASA 2015)

    daphelion = 152.10 Gm = furthest sun-Earth distance, which occurs about 4 July (NASA 2015)

    dperihelion = 147.09 Gm = closest sun-Earth distance, which occurs about 3 January (NASA 2015)

    dr = 173 = 22 June = approx. day of summer solstice

    e = 0.0167 = eccentricity of Earth orbit around sun

    g = –9.80665 m·s–2 = average gravitational acceleration on Earth at sea level (negative = downward) (from 2014 CODATA)

    |g| = go· [1 + A·sin2(ϕ) – B·sin2(2ϕ)] – C·H

    = variation of gravitational-acceleration magnitude with latitude ϕ & altitude H (in meters) above mean sea level. go = 9.7803184 m·s–2, A = 0.0053024, B = 0.0000059, C = 3.086x10–6 s–2

    M = 5.9726 x1024 kg = mass of Earth (NASA 2015)

    Pearth = 365.256 days = Earth orbital period (2015)

    Pmoon = 27.3217 days = lunar orbital period (2015)

    Psidereal = 23.9344696 h = sidereal day = period for one revolution of the Earth about its axis, relative to fixed stars

    Rearth = 6371.0 km = volumetric average Earth radius (from NASA 2015)

    = 6378.1 km = Earth radius at equator

    = 6356.8 km = Earth radius at poles

    S = 1367.6 W ·m–2 = solar irradiance (solar constant) at top of atmosphere (NASA 2015)

    ≈ 1.125 K ·m ·s–1 = kinematic solar constant (based on mean sea-level density)

    Te = 254.3 K = effective radiation emission black-body temperature of Earth system (NASA 2015)

    Φr = 23.44° = 0.4091 radians = tilt of Earth axis = obliquity relative to the orbital plane (2015)

    Ω = 0.7292107 x10–4 s–1 = sidereal rotation frequency of Earth (NASA 2015)

    2·Ω = 1.458421 x10–4 s–1 = Coriolis factor

    2·Ω / Rearth = 2.289 x10–11 m–1 ·s–1 = beta factor

    B.4. Air and Water Characteristics 

    a = 0.0337 (mm/day) ·(W/m2)–1 = water-depth evaporation per unit latent-heat flux

    B = 3 x109 V·km–1 = breakdown potential for dry air

    Cvd = 717 J·kg–1·K–1 = specific heat for dry air at constant volume

    Cpd = 1003 J·kg–1·K–1 = specific heat for dry air at constant pressure at –23°C

    = 1004 J·kg–1·K–1 = specific heat for dry air at constant pressure at 0°C

    = 1005 J·kg–1·K–1 = specific heat for dry air at constant pressure at 27°C

    Cpv = 1850 J·kg–1·K–1 = specific heat for water vapor at constant pressure at 0°C

    = 1875 J·kg–1·K–1 = specific heat for water vapor at constant pressure at 15°C

    Cliq = 4217.6 J·kg–1·K–1 = specific heat of liquid water at 0°C

    Cice = 2106 J·kg–1·K–1 = specific heat of ice at 0°C

    D = 2.11x10–5 m2·s–1 = molecular diffusivity of water vapor in air in standard conditions

    eo = 0.611 kPa = reference vapor pressure at 0°C

    k = 0.0253 W·m–1·K–1 = molecular conductivity of air at sea level in standard conditions

    Ld = 2.834x106 J·kg–1 = latent heat of deposition at 0°C

    Lf = 3.34 x105 J·kg–1 = latent heat of fusion at 0°C

    Lv = 2.501 x106 J·kg–1 = latent heat of vaporization at 0°C

    n = 3.3 x1028 molecules ·m–3 for liquid water at 0°C

    nair ≈ 1.000277 = index of refraction for air

    nwater ≈ 1.336 = index of refraction for liquid water

    nice ≈ 1.312 = index of refraction for ice 

    PSTP = 101.325 kPa = standard sea-level pressure (STP = Standard Temperature & Pressure)

    d = 0.287053 kPa·K–1·m3·kg–1 = Cpd – Cvd

    = 287.053 J·K–1 ·kg–1 = gas constant for dry air

    v = 461.5 J·K–1·kg–1 = water-vapor gas constant 

    = 4.61 x10–4 kPa·K–1·m3·g–1

    Ric = 0.25 = critical Richardson number (dimensionless)

    so = 343.15 m·s–1 = sound speed in standard, calm air

    TSTP = 15°C = standard sea-level temperature

    ε = 0.622 gwater·gair–1 = ℜd / ℜv = gas-constant ratio

    γ = 0.0004 (gwater·gair–1)·K–1 = Cp / Lv

    = 0.4 (gwater·kgair–1)·K–1 = psychrometric constant

    Γd = 9.75 K·km–1 = |g|/Cp = dry adiabatic lapse rate

    ρSTP = 1.225 kg·m–3 = standard sea-level air density

    ρavg = 0.689 kg·m–3 = air density averaged over the troposphere (over z = 0 to 11 km)

    ρliq = 999.84 kg·m–3 = density of liquid water at 0°C

    = 1000.0 kg·m–3 = density of liquid water at 4°C

    = 998.21 kg·m–3 = density of liquid water at 20°C

    = 992.22 kg·m–3 = density of liquid water at 40°C

    = 983.20 kg·m–3 = density of liquid water at 60°C

    = 971.82 kg·m–3 = density of liquid water at 80°C

    = 958.40 kg·m–3 = density of liquid water at 100°C

    ρsea-water = 1025 kg·m–3 = avg. density of sea water (sea water contains 34.482 g of salt ions per kg of water, on average)

    ρice = 916.8 kg·m–3 = density of ice at 0°C

    σ = 0.076 N·m–1 = surface tension of pure water at 0°C

    B.5. Conversion Factors & Combined Parameters

    Cpd / Cvd = k = 1.400 (dimensionless) = specific heat ratio 

    Cpd /|g| = 102.52 m·K–1

    Cpd / Lv = 0.0004 (gwater·gair–1)·K–1 = γ

    = 0.4 (gwater·kgair–1)·K–1

    = psychrometric constant

    Cpd / ℜd = 3.50 (dimensionless)

    Cvd / Cpd = 1/k = 0.714 (dimensionless)

    |g|/Cpd = Γd = 9.8 K·km–1 = dry adiabatic lapse rate

    |g|/ ℜd = 0.0342 K·m–1 = 1/(hypsometric constant)

    Lv / Cpd = 2.5 K/(gwater·kgair–1)

    Lv / ℜv = 5423 K = Clausius-Clapeyron parameter for vaporization

    d / Cpd = 0.28571 (dimensionless) = potential-temperature constant

    d /|g| = 29.29 m·K–1 = hypsometric constant

    ρair ·Cpd air = 1231 (W·m–2) / (K·m·s–1) at sea level

    = 12.31 mb·K–1 at sea level

    = 1.231 kPa·K–1 at sea level

    ρair ·|g| = 12.0 kg·m–2·s–2 at sea level

    = 0.12 mb·m–1 at sea level

    = 0.012 kPa·m–1 at sea level

    ρair ·Lv = 3013.5 (W·m–2) / [(gwater·kgair–1)·(m·s–1)] at sea level

    ρliq ·Cliq = 4.295 x106 (W·m–2) / (K·m·s–1

    1 megaton nuclear explosion ≈ 4x1015 J

    2π radians = 360°

    (1–ε)/ε = 0.61 = virtual temperature constant

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