median mass [OCEANOGR] The average height of the lower low waters at a place over a 19-year period. { me¯n ¦lo¯⭈ər lo¯ wo˙d⭈ər } mean lower low-water springs [OCEANOGR] The average height of lower low-water springs at a place. { me¯n ¦lo¯⭈ər ¦lo¯¦wo˙d⭈ər spriŋz } mean low water [OCEANOGR] The average height of all low waters recorded at a given place over a 19-year period. { me¯n lo¯ wo˙d⭈ər } mean low-water lunitidal interval [OCEANOGR] The average interval of time between the transit (upper or lower) of the moon and the next low water at a place. { me¯n ¦lo¯ ¦wo˙d⭈ər ¦lu¨⭈nə¦tı¯d⭈əl in⭈tər⭈vəl } mean low-water neaps [OCEANOGR] The average height of the low water at neap tides. Also known as low-water neaps; neap low water. { me¯n ¦lo¯ ¦wo˙d⭈ər ne¯ps } mean low-water springs [OCEANOGR] The average height of the low waters of spring tides; this level is used as a tidal datum in some areas. Also known as low-water springs; spring low water. { me¯n ¦lo¯ ¦wo˙d⭈ər spriŋz } mean map See mean chart. { me¯n map } mean neap range See neap range. { me¯n ne¯p ra¯nj } mean neap rise [OCEANOGR] The height of mean high-water neaps above the chart datum. { me¯n ne¯p rı¯z } mean range [OCEANOGR] The difference in the height between mean high water and mean low water. { me¯n ra¯nj } mean rise interval [OCEANOGR] The average interval of time between the transit (upper or lower) of the moon and the middle of the period of rise of the tide at a place; it may be either local or Greenwich, depending on the transit to which it is referred, but the local interval is assumed unless otherwise specified. { me¯n rı¯z in⭈tər⭈vəl } mean rise of tide [OCEANOGR] The height of mean high water above the chart datum. { me¯n rı¯z əv tı¯d } mean river level [HYD] The average height of the surface of a river at any point for all stages of the tide over a 19-year period. { me¯n riv⭈ər lev⭈əl } mean sea level [OCEANOGR] The average sea surface level for all stages of the tide over a 19-year period, usually determined from hourly height readings from a fixed reference level. { me¯n se¯ lev⭈əl } mean spring range See spring range. { me¯n spriŋ ¦ra¯nj } mean spring rise [OCEANOGR] The height of mean high-water springs above the chart datum. { me¯n spriŋ ¦rı¯z } mean temperature [METEOROL] The average temperature of the air as indicated by a properly exposed thermometer during a given time period, usually a day, month, or year. { me¯n tem⭈prə⭈chər } mean tide See half tide. { me¯n tı¯d } mean tide level [OCEANOGR] The tide level halfway between mean high water and mean low water. { me¯n tı¯d lev⭈əl } mean water level [OCEANOGR] The average surface level of a body of water. { me¯n wo˙d⭈ər lev⭈əl } mechanical erosion See corrasion. { mi kan⭈ə⭈kəl i ro¯⭈zhən } mechanical instability See absolute instability. { mi kan⭈ə⭈kəl in⭈stə bil⭈əd⭈e¯ } mechanical sediment See clastic sediment. { mi kan⭈ə⭈kəl sed⭈ə⭈mənt } mechanical turbulence [METEOROL] Irregular air movement in the lower atmosphere resulting from obstructions, for example, tall buildings. { mi kan⭈ə⭈kəl tər⭈byə⭈ ləns } mechanical weathering [GEOL] The process of weathering by which physical forces break down or reduce a rock to smaller and smaller fragments, involving no chemical change. Also known as physical weathering. { mi kan⭈ə⭈kəl weth⭈ə⭈riŋ } medial moraine [GEOL] 1. An elongate moraine carried in or upon the middle of a glacier and parallel to its sides. 2. A moraine formed by glacial abrasion of a rocky protuberance near the middle of a glacier. { me¯⭈de¯⭈əl mə ra¯n } median mass [GEOL] A less disturbed structural block in the middle of an orogenic belt, bordered on both sides by orogenic structure, thrust away from it. Also known as betwixt mountains; Zwischengebirge. { me¯⭈de¯⭈ən mas } mean lower low water
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