Monarch-Aann model of global annual sea surface anomalies  

The Monarch-Aann model consists of 4 grids that can be downloaded in either GRAVSOFT format (.grd) or line text format (.xyz). Along with the gridfiles is a stand-alone Fortran program "extract_ann_signal.f" that can be used to extract the annual sea surface phase and amplitude variations from the .grd files.

			- Monarch-A_ANN_cos.grd or Monarch-A_ANN_cos.xyz
			- Monarch-A_ANN_sin.grd or Monarch-A_ANN_sin.xyz
			- Monarch-A_ANN_amp.grd or Monarch-A_ANN_amp.xyz
			- Monarch-A_ANN_pha.grd or Monarch-A_ANN_pha.xyz
			- extract_ann_signal.f

The Monarch-Aann has been calculated from the global model GECCO using data from 1992-2004. 
GECCO is a part of ECCO (National Ocean Partnership Program (NOPP). In a test of 4 sea surface height models GECCO proved to be the best compared to altimetry data from TOPEX/JASON (+-66deg), ERS-2/ENVISAT (+-82) and ICESAT (+-88) in the period from 1995-2010. In many regions the amplitude and phase signals returned from the model data ahd to be adjusted to the altimetry data to obtain Monarch-Aann.
17 years of joint T/P-Jason1 andJason2 have been used to compute annual sea level modifications and to adjust the model for wavelength longer
than 300 km. In the Arctic Ocean tide gauges have been used to adjust the model 
All adjustmens are only applied to the amplitude of the GECCO model. The phase remains unchanged. 


The program can be compiled by standard Fortran compilers and run. 

Input: 
	Time_dec. Time in decimal years. eg if the phase you want the phase from january 29. Input  29/365 =0.0795.
	Lat in degrees. [-90,90]
	Lom in degrees. [-90,90]

Output:
      Dhann(time_dec,lat,lon). Predicted annual sea level variations in [meter] 
	Amp(lat,lon).            Predicted Amplitude in [meter]
	Phase(lat,lon).          Predicted Phase in degrees [-180,180] 
	Sin(lat,lon).            Predicted Sine value in [rad] 
	Cos(lat,lon).            Predicted Cosine value in [rad]

Bilinear interpolation is used to find the predicted amplitude, cosine and sine grid values from a given (lat,lon). 

The phase is calculated by:

f_xy_pha = 360*ATAN2(f_xy_sin,f_xy_cos)/topi

and the annual sea level variations is calculated as:

dhann(t) = f_xy_amp*cos(time_rad-f_xy_pha*topi/360), where time_rad=2pi*time_dec


Version is available in which altimetry using the IB (DAC - Dynamic Atmosphere Correction (IB + High Frequency) correction 
has been applied and in a version where this correction has not been applied. 
The Arctic Ocean exhibit a particularly strong difference between the two fields. 

For more details contact Ole B. Andersen at oa@space.dtu.dk.