Himalayan meteorology: Weather – February 2006, Vol. 61, No. 2
Practical research at high altitude Elizabeth J. Kennett Imperial College, London As a mountaineer, I have spent many hours agonising over the weather forecast, knowing that a correct interpretation is crucial for the safety and success of any trip. I have also experienced at first hand the sudden changes in the weather that are notorious in high mountain regions. Mountaineering has undoubtedly heightened my understanding of the weather and inspired a keen interest in meteorology. In September 2004, I was fortunate enough to have the opportunity of combining meteorological research with the ascent of a Himalayan peak. I joined a team who were attempting Cho Oyu, which is located 20 km west of Mount Everest and, at 8201 m, is the sixth highest mountain in the world. My primary role was to try to retrieve a barometer that had been previously left on the mountain, and also place a new instrument at a suitable site above 8000 m. This work formed part of the Himalayan Atmospheric Pressure (HIMAP) Project.
Importance of Himalayan weather and climate
44
The Himalayas have a profound dynamical and thermodynamical influence on the atmosphere, affecting both the local and global climate. They act as a physical barrier to the flow of air, lead to the forcing of planetary-scale waves, and also significantly modify the atmospheric circulation through associated latent heating. During winter, the high Himalayas interact with the strong winds of the upper-level subtropical jet stream (Moore 2004). During summer, moist southerly flows from the Bay of Bengal impact on the Himalayas, with the subsequent release of latent heat playing an important role in amplifying the circulation of the monsoon (Kennett and Toumi 2005). The Himalayas are also the source of three of the world’s largest rivers, the Indus, Ganges and Brahmaputra, which supply water to hundreds of millions of people.
High mountainous regions are particularly vulnerable to changes in climate. Models predict that surface temperature changes due to increasing greenhouse gases are likely to be greater at high elevations. For example, current models predict that by the end of the century surface warming over the Tibetan Plateau will exceed the global average by greater than 40%, for a 1% increase in CO2 per year (IPCC 2001). This is largely due to positive feedback from changes in surface albedo, and the dramatic decreases in the size of mountain glaciers observed in recent years (IPCC 2001) are consistent with this. An understanding of the interactions between weather systems and the complex Himalayan topography is essential if we are to make accurate predictions of future climate change in the region. However, substantial uncertainty in weather and climate processes in the Himalayas remains, partly due to the lack of meteorological observations in this remote region. For example, there are no radiosonde stations in the central Himalayas and nearly all raingauges are located at the bottom of valleys (Lang and Barros 2002). The Pyramid Meteorological Observatory at 5050 m near Mount Everest is located in the semi-arid inner Himalaya
and conditions here are unrepresentative of those on the south-facing slopes or high altitude ridges (Tartari et al. 1999). The recent Tropical Rainfall Measuring Mission (TRMM) is known to underestimate Himalayan rainfall (Barros et al. 2002). The TRMM precipitation radar is unable to detect low precipitation rates and also, in order to eliminate ground clutter artifacts, measurements within about 1 km of the surface are not used in the retrieval of precipitation rate (Anders et al. 2005). Due to their steep and complex topography, representation of the Himalayas in current general circulation models remains a major challenge (Stephenson et al. 1998).
The HIMAP project The HIMAP project is a collaborative project between Imperial College London and the Nepal Department of Hydrology and Meteorology to measure Himalayan atmospheric pressure (HIMAP 2005). The project consists of a network of three barometers located on Mount Everest, Cho Oyu and Shishapangma, which lie in an approximate 80 km long east-west chain (Fig. 1). The aim of the project is to take simultaneous measurements of pressure above 8000 m at
Fig. 1 Locations of the three HIMAP instruments, on Mount Everest, Cho Oyu and Shishapangma
Cho Oyu is a fairly rounded peak and is generally considered to be the easiest of the fourteen 8000 m Himalayan peaks to climb. Nevertheless, on average the success rate of reaching the summit is only about 30%, with failures mainly attributable to altitude sickness or bad weather. There are two main climbing seasons, in April/May before the onset of the monsoon and in September immediately following its withdrawal. During the post-monsoon season, there is a period of a few weeks when the weather is generally good before the Himalayas become exposed to strong winds associated with the re-establishment of the upper-level subtropical jet stream in the region. At this time, the weather on Cho Oyu tends to follow stable cycles with periods of good weather typically lasting several days. At base camp, at 5700 m, temperatures are typically about 10 to 20 °C during the day and –10 to –20 °C during the night. The timescale of the Cho Oyu expedition was five weeks, with the first three weeks spent making successive trips to increasing altitude in order to acclimatise. Levels of oxygen at 8000 m are less than 40% of those at sea-level and without acclimatisation a person at this altitude would be unconscious within minutes. Towards the end of this period, I was able to climb up to the highest camp on the mountain at 7300 m in order to look for an HIMAP instrument that had been placed there during the spring of the previous year. Due to the limited power available, no transmitter had been fitted to the instrument to aid retrieval. A photograph taken at the time of placement, showing the instrument attached to a rock band close to the camp, was the only infor-
task, since there are few obvious features above 8000 m that are exposed postmonsoon, due to the rounded shape of the peak. At about 8100 m we found the last exposed rock before the final snow plateau leading to the summit, and decided this was a suitable site for the instrument (Fig. 2). A GPS reading was taken to mark the instrument position. We were climbing the north-west face of Cho Oyu, and the glorious view of Mount Everest remained hidden until the very last few metres (Fig. 3). We reached the summit at 9 am (local time) and there was so little wind that even the prayer flags lay dormant on the snow. Looking across at Mount Everest, cumulus could already be seen developing in the valleys. As we descended, clouds were seen to rapidly build to the south of the main Himalayan divide (Fig. 4) with a pronounced transition to clear skies over the Tibetan Plateau. Carrying out research at high altitude is extremely difficult. You have to contend with severe cold and frequently strong winds. In some years the weather may be sufficiently unsettled that an opportunity to reach high altitudes does not arise at all. Hazards such as crevasses and avalanches may also be encountered. The thin air and lack of oxygen results in breathlessness and poor co-ordination, and acute mountain sickness, which can be fatal, is a real risk. It can be difficult just to function at these altitudes let alone work, and only the simplest of tasks are possible. All instructions must be clear and precise, with no room for judgement. Two days after returning to Cho Oyu base camp, I was horrified to discover that the HIMAP instrument we had just carefully
Weather – February 2006, Vol. 61, No. 2
Research on Cho Oyu
mation available on its location. During the post-monsoon season the mountains are covered in several feet of snow, so that even prominent features during spring are completely obscured. The difficulty of wading through the deep snow was compounded by the extreme altitude, rendering any search impossible at this time of year. Three weeks into the expedition, the weather deteriorated and we were forced to retreat to base camp in order to wait for an improvement. As time was limited, there was a real possibility that an opportunity to reach the summit might not materialise. After prolonged bad weather, the risk of avalanches is extremely high and several days of good weather are needed to clear the mountain of fresh snow before it is safe to climb. However, fortunately in our case, there was a final good spell of weather before high winds established themselves. This represented our only chance to climb Cho Oyu and to place a new barometer above 8000 m. Just after midnight on the 25 September I left Camp 2 at 7100 m, accompanied by a sherpa, in order to place the barometer and then continue to the summit. It was a perfect night, clear and with no wind. We were nearing 8000 m as the dawn rose, with magnificent and extensive views west along the main Himalayan divide and north across the arid Tibetan Plateau. Above 8000 m we searched for an exposed rock to which the HIMAP instrument could be attached. A suitable site needed to be easily recognisable to aid future retrieval: within relatively easy access of the main climbing route but not too close to avoid disturbance – and away from avalanche prone slopes. On Cho Oyu finding such a site was a difficult
Himalayan meteorology
all three sites, which are sufficiently close to be affected by the same synoptic flow. Measurements of atmospheric pressure give us information on the local and large-scale flow. Mountain station pressure also directly relates to the mean temperature below the mountain and can be used as an indicator of climate change (Toumi et al. 1999). A key advantage of an instrument measuring atmospheric pressure is that it is unaffected by a covering of snow. Any instrument must also be able to operate effectively at temperatures down to about –40 °C, and be light and compact so that it can be easily carried. A Vaisala PTB210 series digital barometer is used, as this is designed to operate in outdoor environments at a wide range of temperatures. The HIMAP instrument data-logger and sensors are powered by lithium batteries with the recorded data being stored on a memory card. Each year, each HIMAP instrument needs to be brought down and replaced so that the data can be retrieved.
Fig. 2 Sherpa placing HIMAP instrument at last exposed rock at about 8100 m. Photograph is taken at about 0700 (local time) looking north towards the cloudless Tibetan Plateau. 45
Weather – February 2006, Vol. 61, No. 2
Himalayan meteorology
ments. Finally, I am grateful to Henry Todd, the Cho Oyu expedition leader, and sherpa Pasany Dawr for their help in carrying out work on the mountain. HIMAP is funded by the National Environmental Research Council (NERC) and from the Philip Leverhulme Prize awarded to Dr Toumi.
References
Fig. 3 Summit view from Cho Oyu looking east to Mount Everest, where a second HIMAP instrument is placed, at 0900 (local time) on 25 September 2004. Significant cumulus is already seen developing in the valleys.
Fig. 4 Myself on descent at about 1100 (local time), with the HIMAP instrument in the foreground. Significant cloud is seen building to the south of the main Himalayan divide.
placed on the mountain had been brought down by a fellow climber. The new instrument had been mistakenly identified as another instrument that needed to be retrieved. Fortunately, in this case the error was rectified and the instrument was reinstated a few days later. However, this is illustrative of the mistakes that are all too common at high altitude. For future HIMAP instruments, the feasibility of introducing radio transmitters or tags to aid retrieval is currently being investigated. Also to promote future success, a fixed site for instruments needs to be 46
established on Cho Oyu away from the main climbing trail, with the same individuals responsible for placement and retrieval each year. For me personally, despite the difficulties, it was a privilege to visit such a magnificent place.
Anders, A. M., Roe, G. H., Hallet, B., Montgomery, D. R., Finnegan, N. and Putkonen, J. (2005) Spatial patterns of precipitation and topography in the Himalaya. G.S.A. special Penrose volume (In Press) Barros, A. P., Joshi, M., Putkonen, J. and Burbank, D. W. (2000) A study of the 1999 monsoon rainfall in a mountainous region in central Nepal using TRMM products and rain gauge observations. Geophys. Res. Lett., 27 (22), pp. 3683–3686 HIMAP (2005) http://www.sp.ph.ic.ac.uk/ ~rtoumi/EVE/eve.html IPCC (2001) Climate change 2001: The scientific basis. Contribution of the Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press Kennett, E. J. and Toumi, R. (2005) Himalayan rainfall and vorticity generation within the Indian summer monsoon. Geophys. Res. Lett., 32 (4), art–L04802 Lang, T. J. and Barros, A. P. (2002) An investigation of the onsets of the 1999 and 2000 monsoons in central Nepal. Monthly Weather Review, 130 (5), pp. 1299–1316 Moore, G. W. K. (2004) Mount Everest snow plume: A case study. Geophys. Res. Lett., 31 (22), art–L22102 Stephenson, D. B., Chauvin, F. and Royer, J. F. (1998) Simulation of the Asian summer monsoon and its dependence on model horizontal resolution. Journal of the Meteorological Society of Japan, 76 (2), pp. 237–265 Tartari, G., Verza, G. and Bertolami, L. (1999) Meteorological data at the Pyramid Observatory Laboratory (Khumbu Valley, Sagarmatha National Park, Nepal). Mem. 1st Ital. Idrobiol., 57, pp. 23–40 Toumi, R., Hartell, N. and Bignell, K. (1999) Mountain station pressure as an indicator of climate change. Geophys. Res. Lett., 26 (12), pp. 1751–1754
Correspondence to: Dr E. Kennett, Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College, London e-mail:
[email protected]
Acknowledgments I wish to thank Ralf Toumi, the HIMAP Team Leader, for his support and for allowing me to become involved in this exciting project. I would also like to thank Alan Last for his ongoing hard work designing the instru-
© Royal Meteorological Society, 2006 doi: 10.1256/wea.109.05
