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MPI regional climate model REMO simulations over South Asia
Pankaj Kumar, Ralf Podzun and Daniela Jacob
Max Planck Institute for Meteorology, Hamburg, Germany. e-mail: pankaj.kumar@zmaw.de
1. Abstract:
Climatological features associated with South Asian summer
monsoon (June-Sept.) is examined on intrannual time scale
by Max Planck institute for meteorology (MPI) regional
climate model REMO with a focus over India. The objective
is to validate the model over the region and identify the
strength and weakness of the model. Before making a
climate simulation, various sensitivity experiments have
been performed to validate the model over the region.
Climate simulation have been performed for the period
1979-1993 at 0.5 degree resolution forced by ERA15.
Results showed that the regional model is able to simulate
the mean monsoon climate reasonably well while comparing
with the observed climatologies. The complex topographical
precipitation pattern, and the mean annual cycle of
precipitation and 2m-temperature is well simulated by the
model both over model domain and over the India. Model is
showing a cold temperature bias of nearly 1 deg C in DJF
season and a positive bias over India of nearly same
magnitude in the month of May and June, also during
monsoon season model has simulated 10% less mean
precipitation over India. The circulation pattern simulated by
the model is fairly well though with some limitations.
2. Introduction:
Over 60% of the world population lives over South Asia
(SA). The majority of people over this region depend on
agriculture for their livelihood, that primarily depend on
monsoon rainfall. Rainfall occurrence over this region is
very limited and occurs mainly during summer accounting
70-90% over major part of the region and has a strong
influence on the whole economy of the region. In view of
the importance of SA monsoon on the economy of the
region, it will be interesting to examine the phenomenon
using a regional climate model (RCM).
Climate modelling over SA region is a challenging task due
highly complex interaction between land, ocean and
atmosphere and most of the GCMs fails to simulate the
spatial pattern of precipitation both over land and ocean,
Gadil and Sajaini (1998). Developing a high resolution
models on a global scale is not only computationally
prohibitively expensive for climate change simulations, but
also suffers from errors due to inadequate representation of
climate processes.
Regional model studies over SA, Jacob and Pozdum (1997),
Rupa Kumar et al. (2006), Ratnam et al (2008) have
reported an improvement in the simulation of spatial and
temporal distribution, particularly land precipitation but also
a general over estimation of the rainfall over ocean.
In the present study, Max-Planck Institute for Meteorology,
REgional MOdel (REMO) has been used to the study the SA
summer monsoon with a focus over India to validate the
model over the region for climate change studies.
3. Data and Model:
Data: The observational data of precipitation and surface air
temperature (2m) used to validate the model results have
been taken from Climate Research Unit (CRU) of the
University of East Anglia, which covers the entire globe at a
horizontal resolution of 0.5 0 x 0.5 0 (hereafter referred as
CRU) for the period 1979-1993, New et al. (2000).
The initial and lateral boundary conditions for regional
model simulation is derived from ERA15 at a horizontal
resolution of T106 (1.125 0 x1.1.25 0 ) at a interval of 6hr.
The ERA15 data are interpolated to model grid and levels
to compare the model results.
Model: REMO is a
three dimensional
hydrostatic atmospheric
circulation model
which solve the
discretization primitive
equations of the
atmospheric motion.
REMO, Jacob (2001) is
a combination of two
models, dynamical
core and discretization
in space and time has
been taken from
European Model and
Physics has been taken
from ECHAM4 (GCM
of MPI).
Figure-1: Orography and model
domain over south Asia
Three sensitivity experiment have been performed for the
period 1987-1988 to validate the model over the region.
REMO was run on climate mode with a horizontal
resolution of 0.5 0 (~55 Km) using physical
parametrization scheme from ECHAM4/T106 for the
period 1979-1993 forced by ERA15 reanalysis. Model
domain and topography are shown in in Figure-1, it has
151x109 horizontal grids and 27 vertical levels.
4. Sensitivity experiments
In REMO, soil hydrology can be represented by two ways:
First by a bucket type soil module Dumenil and Todini
(1992) where each gridbox is represented by a single soil
water reservoir i.e. the depth of the bucket and therefore
the water available for evaporation, is defined by the
rooting depth of the plants. This scheme is called without
five soil layer (W5SL). Second, by a five soil layer (5SL)
scheme, in which soil hydrology is defined in five discrete
layers up to 10 meters or bedrock.
The model simulation with 5SL for the period 1987-1988,
shows a positive 2m temperature bias over the Indian
subcontinent when compared to observed CRU, whereas
second simulation for the same period W5SL have shown
a similar result but the magnitude was less compared to
5SL. In REMO soil has been described as medium moist,
whereas over SA, soil is basically dry throughout the year
except for the monsoon months, therefore, we have
changed the heat capacity and diffusivity of the soil from
medium moist type to dry type Gordon B. (2002) and
made a third simulation (Ref) for the same period. Results
are presented in the figure-2. Upper panel is the difference
from Ref to W5SL, which show a significant realistic drop
in 2m temperature over Indian subcontinent by 2-4 0 C,
whereas middle panel show the difference form Ref to