Improvement of HIRHAM Orographic Data over the Greenland Ice Sheet

Jason E. Box Polar Meteorology Group, Byrd Polar Research Center, Ohio State University, USA, box.11@osu.edu
Annette Rinke Alfred Wegener Institut, Potsdam, Germany, arinke@awi-potsdam.de
Klaus Dethloff  Alfred Wegener Institut, Potsdam, Germany, dethloff@awi-potsdam.de

August, 2002

What is HIRHAM?

Introduction
    Elevation biases over Greenland have been uncovered by comparison of the HIRHAM model data with in-situ Greenland Climate Network data. The elevation biases lead to model errors over Greenland and probably have downstream effects on pan-arctic regional climate simulations with the HIRHAM model (Box and Rinke, submitted). Fully-validated elevation data over Greenland (Ekholm) has been inserted into the HIRHAM grid for present modeling efforts. Below are figures and data detailing the improvement in the Arctic orographic model over Greenland. The figures show the HIRHAM elevation distributions over the Arctic region. Greenland is obvious in the figures given that it is the largest orographic feature in the Arctic.
 
 

Figure 1. HIRHAM Arctic orography v1. (US NAVY DEM)

x-axes model domain (100 grid points), y-axes model domain (110 grid points), z-axes: elevation [m].

Figure 2. HIRHAM Arctic orography v2. (GTOPO30 DEM)

x-axes model domain (100 grid points), y-axes model domain (110 grid points), z-axes: elevation [m].

Figure 3. HIRHAM Arctic orography v3. (GTOPO30 DEM with Ekhom Greenland DEM inserted)

x-axes model domain (100 grid points), y-axes model domain (110 grid points), z-axes: elevation [m].

Figure 4. Difference (HIRHAM v2. - HIRHAM v3.)

x-axis model domain (100 grid points), y-axis model domain (110 grid points), z-axis: reduced orography error [m]

Figure 5. GTOPO30 Greenland Bias (GTOPO30-Ekholm) versus latitude

x-axis: latitude, y-axis: elevation bias [m]

Figure 6. Histograms of previous HIRHAM orography bias over Greenland

Summary Statistics
    There is an average negative bias in the GTOPO30 topography over Greenland (including land) of -193 m. The median value is -179 m. See Tables 1 for details of all the elevation data over Greenland on the HIRHAM grid.
 


Table 1. Summary Statistics for Elevation Distributions over Greenland for HIRHAM 50 km Grid
 
USNAVY
GTOPO30
GTOPO30 Ekholm
USNAVY Bias
GTOPO30 Bias
Mean
1729
1649
1830
-101
-181
Median
1884
1809
1979
-99
-156
Mode
393
292
500
-127
-133
Standard Deviation
862
895
866
111
175
Skewness
-0.23
-0.24
-0.26
-0.40
-0.59
Minimum
91
1
135
-610
-840
Maximum
3105
3115
3250
218
332
Count
724
724
724
724
724


HIRHAM Orography Data Sets 
References:
 
  • Bamber, J.L., Ekholm, S. & Krabill, W. B. 2001 A new, high-resolution digital elevation model of Greenland fully validated with airborne laser altimeter data, Journal of Geophysical Research, 106 B4, 6733-6745.
  • Box, J. E. and A. Rinke, Representation of Greenland Ice Sheet Surface Climate in the HIRHAM Regional Climate Model, Journal of Climate, Submitted Dec. 2001.
  • Dethloff, K., A. Rinke, R. Lehmann, J.H. Christensen, M. Botzet, B. Machenhauer: Regional climate model of the Arctic atmosphere. J. Geophys. Res.,101, 23401-23422, 1996
  • Rinke, A., K. Dethloff, A. Spekat, W. Enke, J. H. Christensen, High resolution climate simulations over the Arctic, Polar Res.18 (2), 1-9, 1999
  • Rinke, A., K. Dethloff, J.H. Christensen, M. Botzet, B. Machenhauer: Simulation and validation of Arctic radiation clouds in a regional climate model. J. Geophys. Res., 102, 29833-29847, 1997
    • other HIRHAM publications


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