Geoscience Reference
In-Depth Information
(Cassano, Higgins, and Seefeldt,
2011
) and the Arctic System Reanalysis (ASR)
(Bromwich et al.,
2010
), which will be described later.
HIRHAM:
In its different versions, HIRHAM has been applied variously to the
Arctic, the Antarctic and mid-latitudes. For example, Box and Rinke (
2003
) used
HIRHAM to examine the Greenland Ice Sheet surface climate. HIRHAM draws
from both HIRLAM (High Resolution Limited Area Model - designed for short-
range weather forecasting) and ECHAM, a constantly evolving CGM developed
by the Max Plank Institute for Meteorology. The acronym HIRHAM comes from a
combination of HIRLAM and ECHAM4.
A good example of a regional model application to sea ice processes is that of
Lynch, Maslanik, and Wu (
2001a
), who used the Arctic Regional Climate System
Model (ARCSyM) to simulate the extremely low ice sea extent and concentra-
tion observed over the western Arctic in the summer of 1990. Development of the
open-water feature was examined as a case study in
Chapter 7
from an observa-
tional viewpoint. ARCSyM (Lynch et al.,
1995
), which has been retired, includes a
dynamic-thermodynamic sea ice model. In various simulations, the required driving
fields at the model boundaries have been provided from the NCEP/NCAR reanaly-
sis and ECMWF operational analyses.
Lynch et al. (
2001a
) conducted a control experiment, followed by several sen-
sitivity experiments. The model was initialized on April 15, 1990, and integrated
over a six-month period. Sea ice was initialized to an ice area defined by SSM/I
data, with thickness initialized from output of a ten-year simulation using a differ-
ent stand-alone sea ice model. ARCSyM was forced at the lateral boundaries with
ECMWF operations analyses. The control run simulation reproduced the observed
ice anomaly quite well, along with the major aspects of strong cyclone activity,
early opening of leads and polynyas along the Eurasian coast and enhanced ice melt
that were important to its development (see
Chapter 7
). Sensitivity experiments
a
through
e
used the same configuration as for the control run, except that:
(a) The model was initialized with a uniform 2.0 m ice thickness (PRECON)
(b) The ice dynamics subroutine was turned off (NODYN)
(c) The surface albedo for all grid points was fixed to the initial sea ice albedo
(NOIALB)
(d) The latent heat flux from leads and open water was set to the ice latent heat
flux from ice (NOLHF)
(e) Ice area was constrained to a non-anomalous ice area from May through July
(NOANOM)
Results from these simulations appear in
Figure 9.16
as ice concentrations averaged
for September 1990. They are quite instructive in showing the power of the model
sensitivity experiments in isolating the key mechanisms of ice loss.
Ice concentrations from the NOLHF are quite similar to those from the control
run. This indicates that removing the extra source of moisture represented by open
water has little effect. Given that the ice anomaly pattern from NOLHF is very
similar to that of the control run (not shown), it can be compared with anomaly
