MT KILIMANJARO SUMMIT CLIMATE STUDY
RESEARCH BY DR. DOUGLAS R HARDY
Senior Research Fellow in the Climate System Research Centre and Department of Geosciences, University of Massachusetts Amherst
Disclaimer: The following discussion and all accompanying figures are for scientific purposes only, to aid in interpreting the climate on Kilimanjaro’s Northern Ice Field. All data should be considered preliminary. Measurement interpretations pertain only to the Northern Ice Field, and may not be representative of conditions elsewhere at the summit, in the surrounding atmosphere, or elsewhere on the mountain. The author and any institutions to which the author is affiliated assume no responsibility for any application of these interpretations or these data, including but not limited to paragliding and hang-gliding activities.
Climate measurements on Kilimanjaro began in February 2000, with installation of an automated weather station (AWS) on the Northern Ice Field. The observation site was chosen to represent climate at the location from which ice cores were simultaneously drilled, through ~50 meters of ice to the crater below. As illustrated in Fig. 1, the AWS is situated in the northwest quadrant of the large summit crater. The mountain’s highest point (Uhuru Peak) is situated on the southern rim of the crater; typical ascent routes (not shown in Fig. 1) are from the southeast (Birafu Camp, Kibo Hut) or west-southwest (Western Breach).
Comprehensive climate measurements continue at the AWS, by instruments which are inspected and/or calibrated at least annually. Figure 2 depicts the current array sensors at the station, and sources of additional information are listed below. The following discussion is based on data from the AWS, for the period March 2000 through September 2011, one of the longest periods of record for a high-elevation station.
The summit of Kilimanjaro reaches well into the large-scale, general atmospheric circulation. At a mean pressure of 506 hPa (equivalent to millibars) it is halfway through Earth’s atmosphere. Without near-surface influences such as forests, land-sea breezes, and topographic barriers, airflow at the summit is quite different from that elsewhere in East Africa (e.g., above the monsoon winds “Kaskazi” (from the northeast, approx. December – March) and “Kusi” (from the southeast, approx. April – October).
On the Northern Ice Field, large-scale airflow is from the east throughout the year. October through April wind is nearly constantly from an azimuth just south of east, with resultant monthly direction varying only between 106 and 110°. Mean monthly wind speed remains rather constant over this period, averaging 6.6 m/s (or 14.6 miles/hour). Rarely does the maximum 1-minute wind speed exceed 20 m/s at any time of year at the AWS.
Wind direction varies only slightly more during the extended dry season of June – September. Accompanying a drop in mean monthly wind speed to ~5 m/s during the dry season, a slight northward direction shift during May and June continues into July, on average reaching 70° (east-northeast). Wind direction then shifts back to east during August and September, with a speed increase typically occurring during the month of September.
FEBRUARY AND MARCH WIND
On an annual basis, the pattern of means and variability for both wind direction and speed are quite similar. Looking more closely at the two-month interval February and March reveals that wind speed during the morning hours averages 7.5 m/s (16.4 miles/hour), usually from the east-southeast. In general, the pattern of speed and direction for 7-day intervals (Fig. 3) shows lowest windspeeds during the first week of February and of March (6.4 and 6.9 m/s, resp.), and highest during the third week of March (8.4 m/s).
Considering the daily cycle, a pronounced decrease in wind speed typically occurs between mid-morning and mid-afternoon (Fig. 4; note that median values are shown for each hour, rather than means). Mean wind speed is at a minimum of 5.0 m/s at 15-16:00 local time on average, and then slowly-but-steadily increases until 8-10:00 (to 8.0 m/s) when it then begins to drop again.
It is important to note that maximum hourly values of 1-minute wind speed show the same diurnal pattern. The afternoon minimum is 7.5 m/s, and the morning maximum is only slightly higher than the mean, at 9.5 m/s.
For a comprehensive overview of the mountain’s glaciers:
Hardy, D.R., 2011. Kilimanjaro. In: Singh, V.P., P. Singh, and U.K. Haritashya (eds.) Encyclopedia of Snow, Ice and Glaciers. Dordrecht: Springer, p. 672-679.
For a short synopsis of initial impressions, as climate and glacier research began in 2000:
Hardy, D.R., 2002. Eternal ice and snow? In Kilimanjaro: to the roof of Africa, A. Salkeld, National Geographic Society, p. 224-225.
Additional scientific publications are also available:
FIG. 1 – Location
Kibo peak of Kilimanjaro, with remnants of the ice cap which once encircled the summit. The crater is the area surrounded by ice and labeled “KIBO.” Contours are in meters. Solid red circle symbol indicates location of an automated weather station (AWS) installed in 2000, and the ice extent is shown for 5 epochs. Abbreviations: NIF, EIF and SIF are the former Northern, Eastern and Southern Ice Fields (respectively); FWG is Furtwängler Glacier; and UP is Uhuru Peak (5,895 m).
FIG. 2 – Automated Weather Station
Automated weather station (AWS) operating on Kilimanjaro’s Northern Ice Field. Climate variables measured include wind speed and direction, incoming and reflected solar radiation, down-welling and outgoing longwave radiation, air temperature and humidity, barometric pressure, and accumulation/ablation of the glacier surface. Uhuru Peak is visible in the background.
FIG. 3 – Wind
Wind Rose diagrams for Kilimanjaro summit wind during February and March mornings. Hourly values from each 7-day interval are depicted in 5° azimuth bins, and the relative frequency of speed is shown in 4 m/s bins. Each interval depicts only measurements made between 06:00 and 13:00, through the period 25 February 2000 to 31 March 2011.
FIG. 4 – Time Of Day
Wind speed box plots for selected hours during February and March (2000 – 2011). Each shaded box encompasses the middle 50% of all measurements for the hour, and the internal line depicts median wind speed. The horizontal lines at the end of each vertical line (“whiskers”) encompass the 10th and 90th percentiles of the distribution, with larger and smaller values shown as dark blue circles. Data for each hour are comprised of 1-minute measurements for the preceding 60 minutes.
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