Index: LMDZ5/trunk/libf/phylmd/StratAer/miecalc_aer.F90
===================================================================
--- LMDZ5/trunk/libf/phylmd/StratAer/miecalc_aer.F90	(revision 2947)
+++ LMDZ5/trunk/libf/phylmd/StratAer/miecalc_aer.F90	(revision 2948)
@@ -60,5 +60,5 @@
   COMPLEX nn
   REAL Q_ext, Q_abs, Q_sca, g, omega   !--parameters for radius r
-  REAL x  !--size parameter
+  REAL x, x_old  !--size parameter
   REAL r, r_lower, r_upper  !--radius
   REAL sigma_sca, sigma_ext, sigma_abs
@@ -70,5 +70,5 @@
   INTEGER bin, Nbin, it
   PARAMETER (Nbin=10)
-
+  LOGICAL smallx
 
 !---wavelengths STREAMER
@@ -347,7 +347,16 @@
       r_lower=exp(log(rmin)+FLOAT(bin-1)/FLOAT(Nbin)*(log(rmax)-log(rmin)))
       r_upper=exp(log(rmin)+FLOAT(bin)/FLOAT(Nbin)*(log(rmax)-log(rmin)))
+      deltar=r_upper-r_lower
+
       r=sqrt(r_lower*r_upper)
       x=2.*RPI*r/lambda_int(Nwv)
-      deltar=r_upper-r_lower
+
+!we impose a minimum value for x and extrapolate quantities for small x values
+      smallx = .FALSE.
+      IF (x.LT.0.001) THEN
+        smallx = .TRUE.
+        x_old = x
+        x = 0.001
+      ENDIF
 
       number=Ntot*deltar/(rmax-rmin) !dN/dr constant over tracer bin
@@ -373,5 +382,5 @@
       ENDIF
 
-      Nstart=Nmax+10
+      Nstart=Nmax+100
 
     !-----------loop for nu1z1, nu1z2
@@ -417,4 +426,5 @@
       Q_sca=0.0
       g=0.0
+
       DO n=Nmax-1,1,-1
         nnn=FLOAT(n)
@@ -426,9 +436,19 @@
               (2.*nnn+1.)/nnn/(nnn+1.) * REAL(a(n)*CONJG(b(n)))
       ENDDO
+
       Q_ext=2./x**2 * Q_ext
       Q_sca=2./x**2 * Q_sca
+    !--extrapolation in case of small x values
+      IF (smallx) THEN
+        Q_ext = x_old/x * Q_ext
+        Q_sca = x_old/x * Q_sca
+      ENDIF
+
       Q_abs=Q_ext-Q_sca
+
       IF (AIMAG(m).EQ.0.0) Q_abs=0.0
       omega=Q_sca/Q_ext
+
+    ! g is wrong in the smallx case (but that does not matter as long as we ignore LW scattering)
       g=g*4./x**2/Q_sca