/* file:  PddSurfaceMassBlance.cpp
   Calculating the surface mass balance using the positive degree day method.
 */

#include "./elements.h"

IssmDouble PddSurfaceMassBlance(IssmDouble* monthlytemperatures, IssmDouble* monthlyprec, IssmDouble* pdds, IssmDouble* pds, IssmDouble signorm, IssmDouble yts, IssmDouble h, IssmDouble s, IssmDouble rho_ice, IssmDouble rho_water){

  // output:
  IssmDouble B;    // surface mass balance, melt+accumulation

  int    iqj,imonth;

  IssmDouble saccu;     // yearly surface accumulation
  IssmDouble smelt;     // yearly melt
  IssmDouble precrunoff;      // yearly runoff
  IssmDouble prect; // total precipitation during 1 year taking into account des. ef.
  IssmDouble water; //water=rain + snowmelt 
  IssmDouble runoff; //meltwater only, does not include rain 
  IssmDouble sconv; //rhow_rain/rhoi / 12 months

  IssmDouble lapser=6.5/1000., sealev=0.;    // lapse rate. degrees per meter. 7.5 lev's 99 paper, 9 Marshall 99 paper
  IssmDouble desfac = 0.5;                 // desert elevation factor
  IssmDouble s0p=0.;         // should be set to elevation from precip source
  IssmDouble s0t=0.;         // should be set to elevation from temperature source
  IssmDouble st;             // elevation between altitude of the temp record and current altitude
  IssmDouble sp;             // elevation between altitude of the prec record and current altitude

  // PDD and PD constants and variables
  IssmDouble siglim;          // sigma limit for the integration which is equal to 2.5 sigmanorm
  IssmDouble signormc = signorm - 0.5;     // sigma of the temperature distribution for cloudy day
  IssmDouble siglimc, siglim0, siglim0c;
  IssmDouble PDup, pddsig, PDCUT = 2.0; // PDcut: rain/snow cutoff temperature (C)
  IssmDouble DT = 0.02;
  IssmDouble pddt, pd; // pd: snow/precip fraction, precipitation falling as snow

  IssmDouble q, qmpt; // q is desert/elev. fact, hnpfac is huybrect fact, and pd is normal dist.
  IssmDouble qm = 0.;        // snow part of the precipitation 
  IssmDouble qmt = 0.;       // precipitation without desertification effect adjustment
  IssmDouble qmp = 0.;       // desertification taken into account
  IssmDouble pdd = 0.;     
  IssmDouble frzndd = 0.;  

  IssmDouble tstar;          // monthly mean surface temp
  IssmDouble Tsum= 0.;       // average summer (JJA) temperature
  IssmDouble Tsurf = 0.;     // average annual temperature    

  IssmDouble deltm=1./12.;
  int    ismon[12]={11,0,1,2,3,4,5,6,7,8,9,10};

  IssmDouble snwm;  // snow that could have been melted in a year.
  IssmDouble snwmf; //  ablation factor for snow per positive degree day.
  IssmDouble smf;   //  ablation factor for ice per pdd (Braithwaite 1995 from tarasov 2002).

  IssmDouble dfrz=1.5, CovrLm=2009./3.35e+5, dCovrLm=dfrz*CovrLm; //m*J kg^-1 C^-1 /(J kg^-1)=m/C yr
  IssmDouble supice,supcap,diffndd;
  IssmDouble fsupT=0.5,  fsupndd=0.5;  // Tsurf mode factors for supice
  IssmDouble pddtj, hmx2;

  sconv=(rho_water/rho_ice)/12.; //rhow_rain/rhoi / 12 months

  /*PDD constant*/
  siglim = 2.5*signorm; 
  siglimc = 2.5*signormc;
  siglim0 = siglim/DT + 0.5;
  siglim0c = siglimc/DT + 0.5;
  PDup = siglimc+PDCUT;

  // seasonal loop
    for (iqj = 0; iqj < 12; iqj++){
      imonth =  ismon[iqj];

      st=(s-s0t)/1000.;
      tstar = monthlytemperatures[imonth] - lapser *max(st,sealev);
      Tsurf = tstar*deltm+Tsurf;        

      /*********compute PD ****************/
      if (tstar < PDup){
	pd = 1.;
	if (tstar >= -siglimc){ pd = pds[reCast<int,IssmDouble>(tstar/DT + siglim0c)];}}
      else { 
	pd = 0.;}

      /******exp des/elev precip reduction*******/
      sp=(s-s0p)/1000.; // deselev effect is wrt chng in topo
      if (sp>0.0){q = exp(-desfac*sp);}
      else {q = 1.0;}

      qmt= qmt + monthlyprec[imonth]*sconv;  //*sconv to convert in m of ice equivalent per month
      qmpt= q*monthlyprec[imonth]*sconv;           
      qmp= qmp + qmpt;
      qm= qm + qmpt*pd;

      /*********compute PDD************/
      // ndd(month)=-(tstar-pdd(month)) since ndd+pdd gives expectation of
      // gaussian=T_m, so ndd=-(Tsurf-pdd)
      if (iqj>5 &&  iqj<9){ Tsum=Tsum+tstar;} 
      if (tstar >= siglim) {pdd = pdd + tstar*deltm;}
      else if (tstar> -siglim){
	pddsig=pdds[reCast<int,IssmDouble>(tstar/DT + siglim0)];
	pdd = pdd + pddsig*deltm;
	frzndd = frzndd - (tstar-pddsig)*deltm;}
      else{frzndd = frzndd - tstar*deltm; }
  } // end of seasonal loop 

  //******************************************************************
    saccu = qm;
    prect = qmp;     // total precipitation during 1 year taking into account des. ef.
    Tsum=Tsum/3;

    /***** determine PDD factors *****/
    if(Tsum< -1.) {
      snwmf=2.65*0.001;   //  ablation factor for snow per positive degree day.*0.001 to go from mm to m/ppd
      smf=17.22*0.001;    //  ablation factor for ice per pdd (Braithwaite 1995 from tarasov 2002)
    } 
    else if(Tsum< 10){
      snwmf = (0.15*Tsum + 2.8)*0.001;
      smf = (0.0067*pow((10.-Tsum),3) + 8.3)*0.001;
    }
    else{
      snwmf=4.3*0.001;
      smf=8.3*0.001;
    }
    snwmf=0.95*snwmf;
    smf=0.95*smf;

    /*****  compute PDD ablation and refreezing *****/
    pddt = pdd *365;
    snwm = snwmf*pddt;       // snow that could have been melted in a year
    hmx2 = min(h,dfrz);   // refreeze active layer max depth: dfrz

    if(snwm < saccu) {
      water=prect-saccu + snwm; //water=rain + snowmelt
      //     l 2.2= capillary factor
      //     Should refreezing be controlled by frzndd or by mean annual Tsurf?
      //     dCovrLm concept is of warming of active layer (thickness =d@=1-
      //     >2m)
      //     problem with water seepage into ice: should be sealed after
      //     refreezing
      //     so everything needs to be predicated on 1 year scale, except for
      //     thermal
      //     conductivity through ice
      //     also, need to account that melt season has low accum, so what's
      //     going to
      //     hold the meltwater around for refreezing? And melt-time will have
      //     low seasonal frzndd

      //      Superimposed ice :  Pfeffer et al. 1991, Tarasov 2002

      supice= min(hmx2*CovrLm*frzndd+2.2*(saccu-snwm), water); // superimposed ice
      supcap=min(2.2*(saccu-snwm),water);
      runoff=snwm - supice;  //meltwater only, does not include rain
    }
    else {  //all snow melted
      supice= min(hmx2*CovrLm*frzndd, prect );
      runoff= saccu + smf*(pddt-saccu/snwmf) - supice;
      supcap=0;
    }
    //     pdd melting doesn't cool Tsurf, so ndd refreeze shouldn't warm it
    //     except pdd melt heat source is atmosphere, while refreeze is
    //     ground/ice stored interim
    //     assume pdd=ndd, then melt should equal refreeze and Tsurf should=0
    //     assume ndd=2*pdd, then all supice is refrozen, but Tsurf should be
    //     <0
    //     assume ndd>pdd, little melt => little supice 
    //     bottom line: compare for Tsurf<0 : supice and no supice case,
    //     expect Tsurf difference
    //     except some of cooling flux comes from atmosphere//
    //     1 dm supice should not raise Tsurf by 1/dCovrLm = 16.675C
    //     does supice make sense when H< 0.1m? then d=thermoactive ice layer ////
    //     < 0.1 

    //     make more sense to just use residual pdd-ndd except that pdd
    //     residual not clear yet
    //     frzndd should not be used up by refreezing in snow, so stick in
    //     supcap.
    diffndd=0;
    if (frzndd>0) {
      diffndd=fsupndd*min((supice-supcap)/dCovrLm ,frzndd);
      frzndd=frzndd-diffndd;
    }
    if(runoff<0){
      saccu= saccu -runoff;
      smelt = 0;
      precrunoff=prect-saccu;
      //here assume pdd residual is 0, => 
      Tsurf= max(Tsurf,-frzndd);
    }
    else {
      smelt = runoff;
      precrunoff=prect-max(0.,supice)-saccu;}
    //here really need pdd balance, try 0.5 fudge factor?
    //at least runoff>0 => it's fairly warm, so Tsurf is !<<0,
    //yet from site plots, can be ice free with Tsurf=-5.5C
    if(Tsurf<0) {
      Tsurf= min(Tsurf+fsupT*diffndd , 0.);}

    B = -smelt+saccu;
    B = B/yts;
    pddtj=pddt;

  return B;
}
