raceme— A simple, elongated inflorescence with each flower about equally pedicelled. (See Fig. 6.1.)
racemose— Of the nature of a raceme or in racemes.
rachis— The axil of a spike or raceme or of a compound leaf. (See Fig. 6.1.)
radiocarbon— See carbon-14 .
radiometric dating— Calculating an age in years for geologic materials by measuring the presence of a short-life radioactive element (e.g., carbon-14 or potassium/argon-40).
raptor— A bird of prey, such as an eagle, hawk, falcon, or owl.
rawinsonde— A device attached to a helium-filled balloon that, as it ascends, relays radio signals of atmospheric pressure, temperature, and humidity readings while it is being tracked by radar to determine wind velocity at various levels.
reflexed— Abruptly bent downward; deflexed. (See Fig. 6.1.)
regenerated tail— A broken tail that has regrown.
regime— A predominant or characteristic spatial or temporal (seasonal) pattern, as in rainfall.
regolith— A general term for the layer of unconsolidated rock material or debris that forms the surface of the land and overlies bedrock.
relict— An individual or group remaining on the site of a once-larger population; may pertain to plants or animals, or even soils and other geologic features.
resinous— Containing resin or having the shining appearance of being resin-coated.
resonance— The phenomenon of amplification of an atmospheric wave by a forced wave imposed by a boundary condition such as the shape of the terrain profile in the form of parallel mountain ranges.
reticulate— A color pattern consisting of linear markings resembling the meshes of a net.
reverse fault— An inclined fault in which the rocks above the hanging wall (above the fault plane) have moved up relative to those below the foot wall (below the fault plane).
rhizome— An underground stem or rootstock that roots as it progresses, commonly described as running rootstock; a type of rootstock with scales at the nodes that become leafy shoots above.
ridge— An anticyclonic (clockwise) bend in the horizontal airflow pattern in the synoptic (weather map) scale.
rime icing— An opaque formation of ice formed by the rapid freezing of supercooled water drops as they impinge upon a solid object.
riparian— Descriptive of plants located on watercourses or along bodies of water.
roche moutonée— A glacially sculpted knob of bedrock with its long axis oriented in the direction of ice movement; the upstream side is gently inclined, rounded, and striated, with the downstream side steeper and fragmented by plucking. Mountains shaped like sheep (French).
roll cloud— The turbulent cumuliform cloud in the crest of a lee wave; generally forms near or somewhat above mountaintop level.
root crown— An enlarged, commonly woody structure formed at the junction of the root and the stem.
rostral scale— The scale at the tip of the snout.
runway— Pathway used repeatedly by some small rodents.