Note that the associated height rises or falls occur downstream and to the left of the flow, as illustrated in figure 1-3. Divergence  Identification  (Downstream Straightline Flow) The  technique  for  determining  the  areas  of divergence consists in noting those areas where winds of high speed are approaching weaker downstream gradients  that  are  straight.  When  inertia  carries  a high-speed parcel of air into a region of weak gradient, it possesses a Coriolis force too large to be balanced by the weaker gradient force, It is thus deflected to the right. This results in a deficit of mass to the left. The parcels  that  are  deflected  to  the  right  must  penetrate higher pressure/heights and are thus slowed down until they are in balance with the weaker gradient. Then they can be steered along the existing isobaric or contour channels. Divergence  Identification  (Weak  Downstream Cyclonically  Curved  Flow) If the weak downstream gradients are cyclonically curved,  the  divergence  resulting  from  the  influx  of high-speed  wind  is  even  more  marked  due  to  the additional effect of centrifugal forces. Divergence  Identification  (Downstream Anticyclonically  Curved  Flow) The  effect  of  centrifugal  forces  on  anticyclonically curving high-speed parcels is of extreme importance in producing overshooting of high-speed air from sharply curved  ridges  into  adjacent  troughs,  causing  pressure rises in the west side of the troughs. Divergence  Identification  (Strong  Winds) If   high-speed   parcels   approach   diverging cyclonically curved contours, large contour falls will occur  downstream  to  the  left  of  the  high-speed  winds. Eventually  a  strong  pressure  gradient  is  produced downstream,  to  the  right  of  the  high-speed  winds, chiefly as a result of pressure falls to the left of the direction  of  high-speed  winds  in  the  cyclonically  curved contours with weak pressure gradient. Usually the deflection of air toward higher pressure is so slight that it  is  hardly  observable  in  individual  wind  observations. However,  when  the  pressure  field  is  very  weak  to  the tight of the incoming high-speed stream, noticeable angles between the wind and contours may be observed, especially at lower levels, due to transport of momentum downward as a result of subsidence, where the gradients are even weaker. This occurs sometimes to such an extent that the wind flow is considerably more curved anticyclonically than the contours. In rare cases this results in anticyclonic circulation centers out of phase with  the  high-pressure  center.  This  is  a  transitory condition necessitating a migration of the pressure center toward the circulation center. In cases where the high-pressure center and anticyclonic wind flow center are out of phase, the pressure center will migrate toward the circulation center (which is usually a center of mass convergence). It is more normal, however, for the wind component toward high pressure to be very slight, and unless the winds and contours are drawn with great precision, the deviation  goes  unnoticed. Overshooting High-speed  winds  approaching  sharply  curved ridges result in large height rises downstream from the ridge due to overshooting of the high-speed air. It is known from the gradient wind equation that for a given pressure  gradient  there  is  a  limiting  curvature  to  the trajectory of a parcel of air moving at a given speed. Frequently   on   upper   air   charts,   sharply   curved stationary ridges are observed with winds of high speed approaching the ridge. The  existence  of  a  sharply curved extensive ridge usually means a well-developed trough downstream, and frequently a cold or cutoff low exists in this trough. The high-speed winds approaching the ridge, due to centrifugal forces, are unable to make the sharp turn necessary to follow the contours. These winds overshoot the ridge anticyclonically, but with less curvature than the contours, resulting in their plunging across   contours   toward   lower   pressure/heights downstream from the ridge. This may result in anyone of  a  number  of  consequences  for  the  downstream trough, depending on the initial configuration of the ridge and trough, but all of these consequences are based on the convergence of mass into the trough as a result of overshooting of winds from the ridge. Four  effects  of  overshooting  areas  follows: 1. Filling of the downstream trough. This happens if the contour gradient is strong on the east side of the trough; that is, a blocking ridge to the east of the trough. 2.  Acceleration  of  the  cutoff  low  from  of  its stationary position. This usually occurs in all cases. 1-5