106
north-south gradient in temperature near the northern and north-east parts of India
and on the foot hills of Himalaya have more sharp features than that in CRU
(Fig. 2c). The precipitation amount simulated by the WRF model is more than that
of GPCC. While the precipitation amount over the western Himalaya and Hindukush
mountains is about 3–4 mm/day, the model simulates patches of precipitation
exceeding 8–10 mm/day over the higher reaches. It may be noted here that observed
precipitation data especially over the inaccessible higher reaches of the Himalaya
are not available. In that case, the coarse resolution GPCC data does not contain any
information on precipitation over such regions and therefore, the precipitation plot
in Fig. 1b looks smoother with lower amount. However, the WRF model with 8 km
resolution is able to take in to account the precipitation processes occurring at high
altitudes over the mountains and simulates the precipitation in Fig. 2d.
Because of the rugged terrain and inaccessibility to the higher reaches, a poor
snow gauge network exists in the high altitude region of the Himalaya. Remote
sensing remains the most important means of obtaining some information on the
snowpack. Snow water equivalent (SWE) describes the amount of water stored
within the snowpack that would be available upon melting and is a major driver of
local snowmelt release and hydrological cycles (Derksen et al. 1998). The availability of spatially and temporally extensive SWE data enables a better understanding of space-time trends in snow cover. Tiwari et al. (2016a) have examined the
seasonal variations of SWE over the western Himalaya using remotely sensed data
from National Snow and Ice Data Centre (NSIDC), USA. However, such data are
only for large scale studies and it is not possible to study the detailed structure of
snowfall and snow amount using such data. In such a situation high-resolution modeling studies provide an alternate method to examine the snow amount and snow
cover structure over the Himalaya. Figure 3a shows the WRF model simulated SWE
climatology for DJF period. It is seen that the model simulated SWE pattern is
almost the same as the precipitation pattern shown in Fig. 2d. The Hindukush,
Karakoram and the region to the north, the Pir Panjal range receive more than
7–8 mm/day snow. Snowfall occurring over the eastern parts of the study region and
Tibetan Plateau is very less (about 1 mm/day or less). In order to examine the proportion of liquid and solid precipitation over the region, ratio of snow to total precipitation has been computed as shown in Fig. 3b. It is seen that over most parts of
the western Himalaya, especially the higher reaches, during DJF, snow contributes
to the majority (>80%) of total precipitation. Over other regions, snow amount is
less than 50% of the total precipitation. Therefore, it is seen that the model indicates
larger contribution of snow to regional hydrology of the Himalaya.
Figures 4 show the model simulated vertical structures of the seasonally averaged (DJF) upper air temperature (T), zonal (u) and meridional (v) components of
wind. These parameters have been averaged over longitudinal belts from 70°E to
80°E representing western Himalaya and 90°E to 100°E for eastern Himalaya. The
mountainous areas which fall below the specific pressure levels have been masked
by white color in the figures. It is noticed that vertical structure of temperatures
(Fig. 4a, d) are not very different for the western and eastern Himalaya. A south to
north gradient with southern areas warmer than northern areas is seen at all the
S. C. Kar et al.
north-south gradient in temperature near the northern and north-east parts of India
and on the foot hills of Himalaya have more sharp features than that in CRU
(Fig. 2c). The precipitation amount simulated by the WRF model is more than that
of GPCC. While the precipitation amount over the western Himalaya and Hindukush
mountains is about 3–4 mm/day, the model simulates patches of precipitation
exceeding 8–10 mm/day over the higher reaches. It may be noted here that observed
precipitation data especially over the inaccessible higher reaches of the Himalaya
are not available. In that case, the coarse resolution GPCC data does not contain any
information on precipitation over such regions and therefore, the precipitation plot
in Fig. 1b looks smoother with lower amount. However, the WRF model with 8 km
resolution is able to take in to account the precipitation processes occurring at high
altitudes over the mountains and simulates the precipitation in Fig. 2d.
Because of the rugged terrain and inaccessibility to the higher reaches, a poor
snow gauge network exists in the high altitude region of the Himalaya. Remote
sensing remains the most important means of obtaining some information on the
snowpack. Snow water equivalent (SWE) describes the amount of water stored
within the snowpack that would be available upon melting and is a major driver of
local snowmelt release and hydrological cycles (Derksen et al. 1998). The availability of spatially and temporally extensive SWE data enables a better understanding of space-time trends in snow cover. Tiwari et al. (2016a) have examined the
seasonal variations of SWE over the western Himalaya using remotely sensed data
from National Snow and Ice Data Centre (NSIDC), USA. However, such data are
only for large scale studies and it is not possible to study the detailed structure of
snowfall and snow amount using such data. In such a situation high-resolution modeling studies provide an alternate method to examine the snow amount and snow
cover structure over the Himalaya. Figure 3a shows the WRF model simulated SWE
climatology for DJF period. It is seen that the model simulated SWE pattern is
almost the same as the precipitation pattern shown in Fig. 2d. The Hindukush,
Karakoram and the region to the north, the Pir Panjal range receive more than
7–8 mm/day snow. Snowfall occurring over the eastern parts of the study region and
Tibetan Plateau is very less (about 1 mm/day or less). In order to examine the proportion of liquid and solid precipitation over the region, ratio of snow to total precipitation has been computed as shown in Fig. 3b. It is seen that over most parts of
the western Himalaya, especially the higher reaches, during DJF, snow contributes
to the majority (>80%) of total precipitation. Over other regions, snow amount is
less than 50% of the total precipitation. Therefore, it is seen that the model indicates
larger contribution of snow to regional hydrology of the Himalaya.
Figures 4 show the model simulated vertical structures of the seasonally averaged (DJF) upper air temperature (T), zonal (u) and meridional (v) components of
wind. These parameters have been averaged over longitudinal belts from 70°E to
80°E representing western Himalaya and 90°E to 100°E for eastern Himalaya. The
mountainous areas which fall below the specific pressure levels have been masked
by white color in the figures. It is noticed that vertical structure of temperatures
(Fig. 4a, d) are not very different for the western and eastern Himalaya. A south to
north gradient with southern areas warmer than northern areas is seen at all the
S. C. Kar et al.