Clear[x,y,z,t,r]
c = 1;
w = 1;
r=(x^2+y^2)^(1/2);
Et = Abs[x] Sin[w(2 Pi t-r/c)]/r^2;
Export[
"animation.gif",
Table[
ContourPlot[
Et,
{x,-20,20},{y,-20,20},ClippingStyle->Automatic,PlotPoints->30,Axes->False,Frame->False,ColorFunction-> "BlueGreenYellow",ContourStyle->None,Contours->20,
PlotRange->{-.1,.1}],{t,0,9/10,1/10}]]