The Improvement Of EVAD Technology And Application On Artificially Affect Weather

EVAD technology is short for extended velocity azimuth display. It can calculate the vertical mean wind profile above weather radar, vertical mean divergence and vertical mean deformation. EVAD can calculate the widespread echo precipitation, which kind of precipitation usually has relatively uniform wind field. EVAD technology has linear wind assuming, but the real wind field is nonlinear. So in traditional way, the weight is introduced to reduce the influence of nonlinear wind. When the nonlinearity of layers are large, the equidistance circle cannot meet the linear assuming formula, and the traditional EVAD usually calculates the bad representative information. This thesis improves the shortage of traditional EVAD technology. The improved technology only allows the equidistance circle into calculation, which circle meets linear assuming. One way is fixed range. The other way is unset range. The 2 order Fourier fitting RMS error can judge the nonlinearity of equidistance circle. If 2 order Fourier fitting RMS is less or equal to setting threshold, the equidistance circle meet the linear assuming, which can be put into the calculation. Three example is analyzed, which are convectional cumulus rain of Guangzhou, squall line of Hefei and convective-stratiform mixed rain of Xining.Meanwhile, the improved EVAD technology is applied into artificially affect weather, which can offer the favorable information in the precipitation. Two example are analyzed. One is convectional cumulus rain of Guangzhou. The other is convectiv- e-stratiform mixed rain of Xining. The relationship between divergence vertical profi- le above radar and radar parameter is further studied. The radar parameter include the ET, echo volume and so on.The following is the conclusion.(1) When the nonlinearity of wind is relatively small, The threshold 3m/s and trad- itional EVAD technology can calculate out the valued mean wind information. But the threshold 1.5m/s is too small to calculate it.(2) When the nonlinearity of wind is relatively large, the traditional EVAD techno- logy calculates the bad representative mean wind. The threshold 3m/s can avoid it to certain extent. (3) The way of unset range can improve the traditional EVAD technology to some extent, but the different representative range of layers makes the use of EVAD product difficulty.(4) The 2 order Fourier fitting RMS error can judue the nonlinearity of equidistan- ce. So the representation of mean wind profile to real wind field can be characterized by mean RMS of all equidistance circle. The examples show that mean RMS can be on behalf of the representation of mean wind profile to real wind field.(5) The convectional cumulus rain of Guangzhou and convective-stratiform mixed rain of Xining are analyzed by improved EVAD technology. The mean wind profile, mean divergence profile and mean vertical speed of air of examples are researched. The potential of enhancement precipitation is also analyzed. The vertical shear of horizontal wind and convergence of air foreshow the possibility of development furth- erly, the decision of the precipitation enhancement must be considered seriously after watch changes of precipitation system. The show of southeast wind of low layers and divergence of air make the echo enhanced and rain rate larger in Guangzhou example. The potential of precipitation enhancement of Guangzhou example is relatively small. The divergence of air of Xining example cannot make the rain rate larger. The reason is no large raindrop formed perhaps, so the potential of precipitation enhancement is relatively large.(6) A light rain example and a heavy are analyzed to study the relationship betwe- en divergence vertical profile above radar and radar parameter. The divergence has relatively good linear relationship with ET and echo volume. The relationship betwee- n divergence and liquid content,rainfall rate are good in heavy rain, but in light rain poor. The reason is that the liquid does not fall fully in light rain, which will affect the relationship between divergence and liquid content, rainfall rate.