Sea breeze wind8/12/2023 ![]() Most familiar among these are the land and sea breezes found along ocean shores and around the larger inland lakes and bays.Ī general wind blowing toward the sea operates against the sea breeze and, if strong enough, may block the sea breeze entirely. Other types of local convective circulations involving both vertical and horizontal movement occur where there are differences in heating between sizable adjacent areas. Enroute, if it should meet colder air beneath it, the down flowing air spreads out on top of the colder layer. These vortexes draw on new supplies of heated air as they move along the surface.Īir that is cooled near the surface almost invariably flows downward along the steepest route available, seeking the lowest levels. Superheated air may escape also in the form of upward-spiraling whirlwinds or dust devils. As they ascend, the bubbles grow by expansion and by mixing with surrounding air. The escaping air usually takes the form of intermittent bubbles that break free and are forced aloft by surrounding denser air. In generally flat terrain, air heated at the surface tends to remain in stagnant layers because of inertia, until it reaches a critical point of instability or is released by mechanical triggering. ![]() These convective currents frequently cause daytime cumulus clouds so often observed over mountain peaks and ridges. Warmed air adjacent to heated slopes tends to be forced upslope to the crest where it flows off in a more-or-less continuous stream. Strong surface heating produces the most varied and complex convective wind systems. Height of the nighttime inversion may usually be located in mountain valleys by traversing side slopes and by taking thermometer readings. In the absence of upper-air soundings, mountaintop and valley-bottom readings give fair approximations of the temperature lapse rate and associated stability or instability. Simultaneous measurements may show significant horizontal temperature gradients. The strong temperature dependence of convective winds make local temperature observations useful indicators of probable wind behavior. ![]() Among the more important are season, diurnal changes, cloud cover, nature of the terrain and its cover such as water, vegetation, or bare ground, and the moisture and temperature structure of the overlying atmosphere. Since they are temperature-dependent, all features of the environment that affect heating and cooling are significant. The nature and strength of convective winds vary with many other factors. The influence of these general winds on the convective wind systems varies with the strength of the general wind, its direction relative to the convective circulation, and the stability of the lower atmosphere. This is somewhat different from common meteorological usage, wherein convection implies upward motion only.Ĭonvective winds may be augmented, opposed, or eliminated by airflow having its origin in the larger pressure systems. Hence, convective winds here refer to all winds-up, down, or horizontal- that have their principal origin in local temperature differences. In different convective circulation systems, either the vertical or the horizontal flow may be the more important but both are part of the same system. Buoyant air is caused to rise by horizontal airflow resulting from the temperature-induced small-scale pressure gradients. Air made buoyant by warming at the surface is forced aloft air which is cooled tends to sink. In the absence of strong synoptic-scale pressure gradients, local circulation in the atmosphere is often dominated by winds resulting from small-scale pressure gradients produced by temperature differences within the locality. Interaction of Valley and Slope Winds with General Winds.These cases, in which the influences of the general winds on fire behavior will predominate, must be recognized. Certainly there will be times when the convective winds will be severely altered or completely obliterated by a strong general wind flow. Those burning in mountain valleys will be influenced by the locally produced valley and slope winds. Fires occurring along a coastline will react to the changes in the land and sea breezes. If their interactions are understood, and their patterns known, the changes in behavior of wildfires can be predicted with reasonable accuracy. In many areas they are the predominant winds in that they overshadow the general winds. Winds of local origin-convective winds caused by local temperature differences-can be as important in fire behavior as the winds produced by the synoptic-scale pressure pattern.
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