Geophysics & Environmental Physics — 60 Terms Defined

Hydrothermal Vents Geophysics & Environmental Physics °C (Vent Fluid Temperature) Fissures on the ocean floor near volcanically active mid-ocean ridges that vent geothermally heated, mineral-rich seawater into the ocean. Geothermally Heated Seawater T ~ 350–400 °C

Ice Core Analysis Geophysics & Environmental Physics Parts per thousand (‰ δ¹⁸O) / ppm (CO₂) The retrieval and paleoclimatological analysis of cylindrical ice samples extracted from deep polar ice sheets and alpine glaciers. Paleotemperature Proxy δ¹⁸O = ((¹⁸O/¹⁶O)_sample / (¹⁸O/¹⁶O)_standard - 1) × 1000‰

Insolation Geophysics & Environmental Physics W/m² or kWh/m²/day The solar electromagnetic radiation power reaching a specified surface area per unit time. S = S₀ (R₀ / R)² cos Z

Ionosphere Geophysics & Environmental Physics Electrons/m³ (Electron Density n_e) An ionized layer of Earth's upper atmosphere (~60 km to 1,000 km) where extreme solar UV and X-ray radiation ionize atmospheric gas atoms into free electrons and ions. Plasma Frequency f_p = (1 / 2π) √(n_e e² / (ε₀ m_e))

Ionospheric Scintillation Geophysics & Environmental Physics Dimensionless S₄ Index Rapid fluctuations in amplitude and phase of satellite radio signals caused by small-scale electron density irregularities in the ionosphere. Scintillation Index S₄ = √(⟨I²⟩ - ⟨I⟩²) / ⟨I⟩

Isostasy Geophysics & Environmental Physics Meters (Crustal Root Depth) The state of gravitational equilibrium between Earth's lithospheric crust blocks floating at depths determined by their thickness and density upon the denser mantle. Airy Model: h_root = h_mountain (ρ_crust / (ρ_mantle - ρ_crust))

La Niña Geophysics & Environmental Physics Sea Surface Temperature Anomaly (°C) The cool climate phase of the El Niño-Southern Oscillation (ENSO) characterized by abnormally cold sea surface temperatures in the central and eastern tropical Pacific. ENSO Index: Southern Oscillation Index (SOI) > 0, Sea Surface Temp Anomaly < -0.5 °C

Lehmann Discontinuity Geophysics & Environmental Physics km (Boundary Depth) The seismic boundary at a depth of ~5,150 km marking the transition between Earth's liquid outer core and solid inner core. Depth z ≈ 5150 km (Outer Core - Inner Core Boundary)

Lithosphere Geophysics & Environmental Physics km (Lithospheric Thickness) The rigid, brittle outermost mechanical shell of Earth comprising the entire crust and uppermost solid mantle. Elastic Thickness h_e ~ 10–200 km

Magnetosphere Geophysics & Environmental Physics Earth Radii (R_E ~ 10 R_E sunward) The region of space surrounding Earth dominated by Earth's geomagnetic field, shielding the planet from harmful solar wind plasma. Magnetopause Distance R_mp ≈ (B₀² / (2 μ₀ ρ v²))^(1/6)

Mantle Convection Geophysics & Environmental Physics cm/year (Convection Motion Speed) The slow, highly viscous thermal convection currents within Earth's solid silicate mantle transporting internal core heat toward the surface. Ra = (ρ g α ΔT d³) / (κ η) (Rayleigh Number > Ra_critical)

Milankovitch Cycles Geophysics & Environmental Physics Geologic Climate Cycles (Years) Cyclical variations in Earth's orbital eccentricity, axial tilt (obliquity), and precession that alter the seasonal and latitudinal distribution of solar insolation. Eccentricity (100ky), Obliquity (41ky), Precession (23ky)

Nutation Geophysics & Environmental Physics Arcseconds (17.2″ in longitude, 9.2″ in obliquity) Small periodic nodding oscillations superimposed upon Earth's long-term rotational axis precession. Principal Nutation Period T = 18.6 years, Amplitude = 9.2″

Ocean Acidification Geophysics & Environmental Physics pH Units (Logarithmic Scale) The ongoing long-term reduction in the pH of Earth's oceans caused by the absorption of anthropogenic carbon dioxide from the atmosphere. CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻, H⁺ + CO₃²⁻ ⇌ HCO₃⁻

Ocean Currents Geophysics & Environmental Physics Sv (Sverdrups = 10⁶ m³/s) or m/s Continuous, directed large-scale movements of seawater generated by wind stress, Coriolis force, temperature, salinity differences, and tides. Geostrophic Ocean Flow: 2 Ω sin φ v_ocean = (1 / ρ) (dP / dx)

Paleoclimatology Geophysics & Environmental Physics Geologic Climate History The scientific study of Earth's past climate conditions across geologic history using indirect environmental proxy records. Climate Proxies: Ice Cores, Tree Rings, Coral δ¹⁸O, Speleothems

Paleomagnetism Geophysics & Environmental Physics Degrees (° Declination / Inclination) The study of the historical record and orientation of Earth's magnetic field preserved in iron-bearing minerals in rocks, sediments, or archaeological artifacts. Remanent Magnetization Vector (Declination & Inclination)

Plate Tectonics Geophysics & Environmental Physics cm/year (Plate Drift Speed) The unifying geophysical theory stating that Earth's rigid outer lithosphere is divided into major tectonic plates drifting over the ductile asthenosphere. Plate Motion Velocity v_plate ~ 1–10 cm/year

Precession of the Equinoxes Geophysics & Environmental Physics Years per Cycle (~25,800 years) The slow continuous conical rotation of Earth's rotational axis in space, taking ~25,800 years to complete one full cycle. Precession Period T ≈ 25,772 years (Axial Wobble Rate ~ 50.3″/year)

Radiative Forcing Geophysics & Environmental Physics W/m² (Watts per square meter) The net change in Earth's energy balance per unit area at the tropopause due to an environmental driver of climate change. ΔF = F_incoming - F_outgoing

Radiometric Dating in Geology Geophysics & Environmental Physics Ma or Ga (Millions / Billions of Years) A geochronological technique used to determine the absolute age of rocks and minerals by measuring radioisotope parent-to-daughter ratios. t = (1 / λ) ln(1 + D / P) (Parent P → Daughter D)

Radon Gas Migration Geophysics & Environmental Physics Bq/m³ or pCi/L (Activity Concentration) The environmental migration of radioactive Radon-222 gas from decaying uranium in rocks and soil into indoor building spaces. Decay Chain: ²³⁸U → ²²⁶Ra → ²²²Rn (Half-life = 3.82 days)

Relative Humidity Geophysics & Environmental Physics Percentage (%) The ratio of the actual vapor pressure of water in an air parcel to the saturation vapor pressure at the same temperature, expressed as a percentage. RH = (e / e_s(T)) × 100%

Remote Sensing in Geophysics Geophysics & Environmental Physics Multi-Spectral Satellite Imagery The acquisition of geophysical information about Earth's surface and atmosphere from a distance using satellite or airborne sensors. NDVI = (NIR - Red) / (NIR + Red)