The gray is the official SI unit of absorbed radiation dose, equal to one joule of ionizing radiation energy absorbed per kilogram of matter. It is used in radiation science, including studies of atmospheric and environmental radiation.
The unit is named after British physicist Louis Harold Gray, whose work focused on the biological effects of radiation. The gray replaced the older rad as the SI-derived unit for absorbed dose. One gray equals 100 rad.
The gray measures energy deposited in material, not the biological harm expected from that exposure. For biological effect, scientists may use the sievert, which applies weighting factors for radiation type and affected tissue. The becquerel instead measures radioactive decays per second, while the joule is a general unit of energy.
Weather affects radiation exposure in several ways. Clouds, aerosols, altitude, snow cover, and atmospheric composition can alter how radiation travels or is reflected. Nevertheless, the gray is a radiation-dosimetry unit rather than a routine weather-observation unit.