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Hydroxyapatite
Hydroxyapatite, also known as calcium hydroxyapatite or hydroxylapatite, is a calcium phosphate mineral with formula Ca10(PO4)6(OH)2 that forms most of human bone and tooth enamel.
Hygrometer
A hygrometer, also called a humidity meter, is an instrument that measures the water vapor content of air, typically as relative humidity or dew point.
HyMeX
HyMeX, the Hydrological Cycle in the Mediterranean Experiment, was a 10-year international research program from 2010 to 2020 studying the Mediterranean water cycle, especially heavy precipitation, flash floods, and droughts.
HYPE (hydrological model)
HYPE (HYdrological Predictions for the Environment) is a semi-distributed catchment model simulating water flow and nutrients, developed at SMHI in Sweden and applied operationally there since 2008.
Hyperspectral change detection
Hyperspectral change detection compares two co-registered hyperspectral images of the same area, acquired at different times, to locate surface changes, with uses in disaster monitoring, land survey, and military reconnaissance.
Hypocenter
A hypocenter, also called the focus, is the point within the Earth where an earthquake rupture starts; the epicenter lies directly above, and focal depth strongly affects shaking intensity.
Hypolimnion
The hypolimnion is the cold, dense bottom layer of a stratified lake, lying beneath the thermocline and cut off from atmospheric oxygen during summer stratification.
Hyporheic zone
The hyporheic zone is the porous region of a stream bed and banks where surface water and shallow groundwater mix, a subsurface environment distinct from both.
Hypsithermal
The Hypsithermal, also known as the Altithermal or Holocene Climatic Optimum, was a warm interval of the mid-Holocene, about 9000 to 5000 years ago, caused by orbital forcing.
Iain Stewart (geologist)
Iain Stewart is a British geologist and BBC presenter who holds the chair of geoscience communication at the University of Plymouth, known for documentaries like Earth: The Power of the Planet.
IBTrACS
IBTrACS, the International Best Track Archive for Climate Stewardship, is a NOAA dataset that unifies global tropical cyclone best-track records from multiple meteorological agencies, spanning the 1840s to the present.
Ice accretion
Ice accretion is the growth of ice on a surface exposed to supercooled water, most prominently on aircraft, where it degrades wing aerodynamics and blocks sensors and engines.
Ice age
An ice age is a long interval of Earth history when continental ice sheets exist at least at the poles. Earth is currently in one, the Late Cenozoic Ice Age.
Ice core
An ice core is a cylindrical sample of ice drilled from a glacier or ice sheet, preserving trapped ancient air that records 800,000 years of climate history.
Ice core chronology
Ice core chronology is the dating framework assigning an age to every depth in a drilled ice core, built by layer counting, ice-flow models, and stratigraphy.
Ice cover dynamics
Ice cover dynamics is the study of the seasonal cycle of freezing, thickening, and thawing on lakes, summarized by ice phenology and used to track climate change.
Ice floe
An ice floe is a flat piece of sea ice 65 feet (20 m) or more across that floats freely, drifting with winds and currents in the polar pack.
Ice lens
An ice lens is a layer of nearly pure ice that forms in freezing soil as water migrates to the freezing front, causing frost heave.
Ice nucleating particles
Ice nucleating particles (INPs) are the rare subset of atmospheric aerosols that trigger ice formation in supercooled clouds, with major sources including mineral dust, biological particles, and sea spray.
Ice pellets
Ice pellets, called sleet in the United States, are transparent ice pellets under 5 mm across that form when rain refreezes in cold air near the ground and usually bounce on impact.
Ice sheet mass balance
Ice sheet mass balance is the net gain or loss of ice on an ice sheet per year, the measure behind the Greenland and Antarctic ice sheets' contribution to sea level rise.
Ice shelf collapse
Ice shelf collapse is the rapid disintegration of a floating Antarctic ice shelf into thousands of small icebergs, as with Larsen A in 1995 and Larsen B in 2002.
Ice storm
An ice storm, also called a silver thaw, is a period of freezing rain that coats trees and power lines with glaze ice, causing widespread outages.
Ice wedge
An ice wedge is a vertical, wedge-shaped mass of ground ice in permafrost, grown over centuries by repeated winter cracking, that forms polygonal patterns across Arctic tundra.
Ice-albedo feedback
The ice-albedo feedback is a positive climate feedback in which warming melts reflective snow and sea ice, exposing darker surfaces that absorb more sunlight and drive further warming.
Ice-jam flood
An ice-jam flood is a flood caused by an accumulation of river ice that blocks the channel, producing water depths two to three times higher than open-water floods at the same flow.
Ice-rafted debris
Ice-rafted debris (IRD), also called ice-rafted detritus, is sediment carried by floating ice and released to the seafloor when it melts, used as a paleoclimate proxy for past iceberg discharge.
Ice-sheet model
An ice-sheet model is a numerical model simulating the flow, thickness, temperature, and mass balance of ice sheets, particularly for predicting their response to climate change under climate forcing.
Ice-Tethered Profiler
The Ice-Tethered Profiler (ITP) is an autonomous oceanographic instrument developed at Woods Hole that profiles the upper ocean beneath drifting Arctic sea ice and transmits data via satellite.
Icelandic Low
The Icelandic Low is a semi-permanent area of low atmospheric pressure over the subpolar North Atlantic, centered between Iceland and southern Greenland, strongest in winter.