isotach


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isotach

[′ī·sə‚tak]
(meteorology)
A line in a given surface connecting points with equal wind speed. Also known as isokinetic; isovel.

isotach

isotachclick for a larger image
A line on a weather chart showing equal, or constant, wind speed. These are generally drawn on high-level charts, generally 500 millibars and higher. These are short dashed lines labeled in knots and are normally indicated for intervals of 20 knots, where space permits. Isotachs, however, do not indicate wind direction.
References in periodicals archive ?
Caption: Figure 4: EAX CWA composite for 0-3 hr prior to event time showing 250 hPa: (a) geopotential height (black, gpm), isotachs (color-filled, kts), and divergence (dashed, x [10.sup.-5] [s.sup.-1]); (b) mean geopotential height (black, gpm) and 75-25 percentile mean spread (color-filled, gpm); (c) mean wind speed (black, kts) and 75-25 percentile mean spread (color-filled, kts); (d) mean divergence (black, x [10.sup.-5] [s.sup.-1]) and 75-25 percentile mean spread (color-filled, x [10.sup.-5] [s.sup.-1]); (e) regional spaghetti plot of the 90-knot isotach at 250 hPa from each composite member (each is a different color).
Caption: Figure 6: EAX CWA composite for 0-3 hr prior to event time showing 850 hPa: (a) geopotential height (black, gpm) and isotachs >20 kts (color-filled); (b) mean geopotential height (black, gpm) and 75-25 percentile mean spread (color-filled, kts); (c) mean isotachs >20 kts (black) and 75-25 percentile mean spread (color-filled, kts); (d) regional spaghetti plot of the 35-knot isotach at 850 hPa from each composite member (each is a different color).
Parameters shown are equivalent potential temperature (solid purple, K), scalar normal isotachs > 60kt (dashed cyan), scaled ageostrophic circulation vectors, and mixing ratio (color-filled, g[kg.sup.-1]).
Caption: Figure 7: (a) 0-h RUC forecast cross-section of normal isotachs (solid black [greater than or equal to] 30 m [s.sup-1] [60kt]), relative humidity (green shading [greater than or equal to] 70%), omega (dashed red negative, [mu] b [s.sup-1]), and a geostrophic circulation (blue vectors), valid at 1800 UTC 11 January 2004; (b) As in Figure 7(a), except valid at 2100 UTC 11 January 2004; (c) As in Figure 7(a), except valid at 0000 UTC 12 January 2004; (d) As in Figure 7(a), except valid at 0300 UTC 12 January 2004; (e) As in Figure 7(a), except valid at 0600 UTC 12 January 2004
In ML case, the isotach viscous load is a unique function of the instantaneous value of [[epsilon].sup.ir] and its rate [[epsilon].sup.ir].
As mentioned earlier, Geosynthetic C (PET geogrid) exhibits the isotach viscosity in continuous ML tests which were carried out at different strain rates and during each lest the strain rate was kept constant.