POKHREL Adarsha P.

UENO Ken\u27ichi

Tsukuba Repository

Inter-annual and intra-seasonal variations of
mountain weather in Khumbu region, Nepal
Himalayas (Session 3: In-site Flux Observation
studies)
著者 UENO Ken'ichi, POKHREL Adarsha P.
journal or
publication title
Bulletin of the Terrestrial Environment
Research Center, the University of Tsukuba,
Proceedings of the International Workshop on
GAME-AAN/Radiation
volume 1
number 別冊
page range 59-62
year 2001-03
URL http://doi.org/10.15068/00147184
Inter-annual and intra-seasonal variations of mountain weather 
in Khum bu region, Nepal Himalayas 
Ken'ichi UEN01 and Adarsha P. POKHREL2 
1) School of Environmental Science, The University of Shiga Prefecture 
Hassaka 2500, Hikone,Shiga, 522-8533 JAPAN 
2) Department of Hydrology and Meteorology 
Babar Mahal, PO.Box 406, Kathmandu HMG/NEPAL 
Automatic Weather Station (AWS) at the 
Syamboche village, Nepal Solu・Khumbu 
district, was established at an altitude of 
3833m a.s.l in October 1994 by the CREH 
project. An observatory exists in a flat 
pasture ground of the Yak farming at the 
middle of the deep valley running 
north-south direction. Such high・eleva叫
station is quite important to monitor the 
climatic change and understand the 
hydro-meteorological processes of the 
Himalayan weather. Meteorological 
elements, such as temperature, humidity, 
wmd, pressure, precipitation, upward and 
downward short-wave radiation, and soil 
temperature are observed with 30 minuets 
interval by AANDERAA AWS. The AWS 
observation was taken over to the 
GAME-AAN project since 1999, and about 5 
years data have been accumulated (Ueno et 
al., 2001). V ariat10n and trends of air 
temperature and diurnal change of the 
monsoon precipitation are analyzed in this 
study. 
Shrinkage of glaciers and glacier lake 
outburst flood are the recent major 
problems in the Nepal in relation to water 
management and prevention of natural 
hazard. Shrestha et al.(1999) showed 
evident mcrease of daily maximum 
temperature in . the Himalayas. To 
investigate the variation and trends of 
surface air temperature at the Syangpoche 
AWS, 5 years record of the 2.3m level air 
temperature are analyzed and compared 
with objective analysis data, and following 
characteristics are found. 
） 1Intra-seasonal variat10n of daily 
temperature was small in the monsoon 
season and quite large in the winter 
season. Amplitude of the daily winter 
temperature exceeded 10℃ causing the 
year・to・year variations (Fig.I). The 
variation was not evident at Kathmandu, 
and showed better correspondence at 
Lhasa in the Tibet although it was 
smaller amplitude. Lower temperature 
days corresponded to the existence of 
snow cover determined by the albedo and 
surface soil temperature condition. 
2) Major warming periods in winter were 
associated with temperature increase 
trough entire days with pressure increase, 
and decrease of downward radiation 
afterward (cloud development) as shown 
in Fig. 2. Diurnal change of the 
mountain-valley wind system continued 
through the period,・ with sporadic 
northerly wind. The warming periods 
showed quite good correspondence to 
high pressures (pressure ridges) in the 
NCEP 500hPa objective analysis data. 
3) 5 years comparison of the monthly AWS 
temperature and 500hPa NCEP 
temperature at a corresponding grid 
location showed that amplitude of the 
month-to-month variation is larger in 
winter and smaller in summer at the 
AWS (Fig. 4). Both data were 
significantly correlated in the winter 
season. Although linear trend of the 
temperature after 1975 was +0.058℃ /y 
m July and +0.042℃ /y in January, 
both correlations were not significant 
statistically. Hemispheric winter 
teleconnection patterns in the 
mid-latitudes (CPC, 1999) relating to the 
AWS monthly temperature variation 
were also not found. 
analysis was performed to the hourly 
precipitation data for the days with 
precipitation (Fig. 5). Frequent 
appearance of second positive patterns in 
the pre-monsoon season (Fac2+), 
corresponding to the morning increase of 
precipitation, was associated with increase 
of albedo and daily temperature below 0℃ 
Namely, this pattern was caused by the 
melting of snow over the tipping bucket 
gauge due to morning insolation. Without 
the snow cover days, daily precipitation 
amount and factor score of the first positive 
pattern (Facl +), increase of precipitation 
from 19:00-2:00 LTM, well correlated. 
Second component (Fac2+, Fac2-) might be 
explaining the modulation of this diurnal 
variation. 
precipitation 
Besides, sporadic 
was observed m 
heavy 
the 
These results indicates that large non-monsoon season affecting year-to-year 
intra-seasonal variations in winter season change of annual precipitation amount. 
were caused by the combinations of 1) cold Daily base analysis by combining of the 
temperature days by the valley scale cooling AWS data and TRMM satellite and GAME 
with snow cover under the weak wind re-analysis data is expected to investigate 
condition, and 2) warm temperature period the synoptic background of precipitation 
associated with passing synoptic scale variability. 
(pressure ridge) system. To investigate the 
response of the local mountain weather to <References> 
the global climate variability, AWS CPC/NOAA, 1999: Standardized Northern 
monitoring will be continued at least 10 Hemisphere Teleconnection Indices. 
years. Shrestha A.B. et al., 1999: Maximum 
Himalayas also play an important 
function as orographical boundary to the 
Indian monsoon system that causes heavy 
precipitations in summer. At Syamboche, 
monsoon precipitation is about 750mm 
(year-to-year variation was less than 
70mm/y) with large diurnal variations. To 
quantify the variation, principal component 
temperature trends in the Himalayas and 
its vicinity. J. Climate. 
Ueno K. et al., 2001: Meteorological 
observations during 1994-2000 at the 
Automatic Weather Station (GEN-AWS) 
in Khumbu region, Nepal Himalayas. 
Bulletin of Glaciological Research. 
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Fig. 2 
WS(m/s) -Down S.Radiation(w/m2)] 
Example of warm period in 1994 winter 
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Fig. 1 5 years record of winter daily, Fig. 3 Comparison of monthly temperature 
minimum and maximum temperature atAWS, 
with daily temperature at Kathmandu and Lhasa. 
between AWS and NCEP 500hPa grid. 
Under bars correspond to days with snow cover atAWS. 
NCEP-500hPa temp. over Syangpoche 
(k) 
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1960 1965 1970 1975 1980 1985 1990 1995 
Fig. 4 Time sequence of the monthly temperature 
for 1958-98 at NCEP 500hPa 27.5N,87.5E grid. 
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Fig. 5 First and second principal component patterns of hourly precipitation as a 
function of local time, composed in positive and negative scores (left), and 
seasonal changes of frequency appearance for each pattern (right). 


Inter-annual and intra-seasonal variations of mountain weather in Khumbu region, Nepal Himalayas (Session 3: In-site Flux Observation studies)

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