Phys - Physics library.

ARJO SEGERS
KNMI

Date: 12/08/2004

Contents

• Introduction
• Geo-potential-height
• Humidity functions
• Convective clouds
• Cloud cover
• Virtual temperature

Introduction

The 'phys' library contains subroutines for model physica.

Geo-potential-height

• Potential height of an air parcel given top and bottom pressure, temperature, and humidity:

       subroutine PotentialHeight( ptop, pdown, T, Q, dh )
         real, intent(in)        ::  ptop, pdown   ! pressure bounds (Pa)
         real, intent(in)        ::  T             ! temperature (K)
         real, intent(in)        ::  Q             ! specific humidity (kg h2o/kg air)
         real, intent(out)       ::  dh            ! geo.pot.height bounds (m)
       end subroutine PotentialHeight
  

• Geo-potential-height at half level boundaries:

       subroutine GeoPotentialHeightB( lm, pb, T, Q, h0, gphb )
         integer, intent(in)            ::  lm         ! number of levels
         real, intent(in)               ::  pb(lm+1)   ! pressure bounds (Pa)
         real, intent(in)               ::  T(lm)      ! temperature (K)
         real, intent(in)               ::  Q(lm)      ! specific humidity (kg h2o/kg air)
         real, intent(in)               ::  h0         ! initial height  (m)
         real, intent(out)              ::  gphb(lm+1) ! geo.pot.height bounds (m)
  

• Geo-potential-height at full levels. A full level has a pressure in between the top and bottom pressure of a layer. Temperature and humidity are assumed to be constant in a layer.

       subroutine GeoPotentialHeight( updo, lm, pb, T, Q, h0, gph )
         integer, intent(in)            ::  lm
         real, intent(in)               ::  pb(lm+1)   ! pressure bounds (Pa)
         real, intent(in)               ::  T(lm)      ! temperature (K)
         real, intent(in)               ::  Q(lm)      ! specific humidity (kg h2o/kg air)
         real, intent(in)               ::  h0         ! initial height  (m)
         real, intent(out)              ::  gph(lm)    ! geo.pot.height (m)
  

Humidity functions

• Saturation specific humidity:

       real function QSat( T, p )
         real, intent(in)   ::  T     ! temperature (K)
         real, intent(in)   ::  p     ! pressure (Pa)
       end function QSat
  

• Derivative of saturation specific humidity with respect to temperature:

       real function dQSat_dT( T, p )
         real, intent(in)   ::  T     ! temperature (K)
         real, intent(in)   ::  p     ! pressure (Pa)
       end function dQSat_dT
  

• Specific humidity given relative humidity, temperature, and pressure:

       real function QH2O( R, T, p )
         real, intent(in)  ::  R     ! rel. humidity (%)   
         real, intent(in)  ::  T     ! temperature (in K)  
         real, intent(in)  ::  p     ! pressure (Pa)       
       end function QH2O
  

Convective clouds

     subroutine ConvCloudDim( updo, lm, detu, entd, &
                              iclbas, ictop, icllfs, &
                              status )

       character(len=1), intent(in)   ::  updo
       integer, intent(in)            ::  lm

       real, intent(in)              ::  detu(lm)
       real, intent(in)              ::  entd(lm)

       character(len=1), intent(in)  ::  updo

       ! cloud base, top, level of free sinking
       integer, intent(out)          ::  iclbas
       integer, intent(out)          ::  ictop
       integer, intent(out)          ::  icllfs

       integer, intent(out)          ::  status

Cloud cover

   subroutine cf_overhead( nlev, yclfr, wccro, scheme, eps )

     integer, intent(in)                     ::  nlev
     real, intent(in)                        ::  yclfr(nlev)
     real, intent(out)                       ::  wccro(nlev)
     character(len=*), intent(in), optional  ::  scheme
     real, intent(in), optional              ::  eps

   input: 
     nlev  : number of vertical levels
     yclfr : cloud fraction (cc) per cell (0-1)
  
   output:
     wccro: overhead cloud fraction
  
   optional arguments:
     scheme='ecmwf'  : 'ecmwf' -> iovln=1
                       'other' -> iovln=0
     eps=1.0e-4      : cltres
  
   parameters:
     iovln : switch
       1 = ecmwf (maximum random overlap assumption) scheme
       0 = another scheme 
     cltres : threshold (minimum) cloud fraction used
              for numerical stability (division by zero
              and to eliminate small unrealistic cloud fractions
  
   Notes: 
   - Index=1 of arrays (yclfr) corresponds to model top
   - The clouds are supposed to be distributed homogeneously
     in the vertical in each layer.

Virtual temperature

• Convert from real temperature and specific humidity to virtual temperature:

       elemental function VirtualTemperature( T, Q )
         real                  ::  VirtualTemperature   ! K
         real, intent(in)      ::  T                    ! real temperature (K)
         real, intent(in)      ::  Q                    ! specific humidity (kg H2O / kg air)
       end function VirtualTemperature
  

• Convert from virtual temperature and specific humidity to temperature:

       elemental function RealTemperature( Tv, Q )
         real                  ::  RealTemperature    ! K
         real, intent(in)      ::  Tv                 ! virtual temper (K)
         real, intent(in)      ::  Q                  ! specific humidity (kg H2O / kg air)
       end function RealTemperature