Monday, January 7, 2013

Snow, lightning

Kilimanjaro was wet through the second half of December, "crazy wet" as characterized by Timba at Ahsante Tours. Telemetry from the Northern Ice Field provides the evidence, with high humidity and snowfall totaling 33.8 cm between 16 December and 3 January. The days of greatest accumulation were the 27th (4.9 cm), 30th (5.2 cm) and 2 January (5.5 cm). Although 5 cm is a moderate hourly rate in some mountain regions, less than 4% of all days with snowfall on Kilimanjaro are of this magnitude. Although such events do not add much mass, they are disproportionally important in terms of raising albedo and thus decreasing net radiation receipt.

Snowfall on the glaciers is often rainfall lower on the mountain, and often much heavier than summit snowfall might suggest. Kilimanjaro precipitation is frequently associated with convection, particularly at this time of year, and at 12:30 PM on Wednesday (2 January), lightning struck a group that was approaching Lava Tower. The group leader Ian McKeever was killed and several other were burned. McKeever's FaceBook post the day before from Shira 2 camp mentioned "torrential rain all day", and the group's guide Said Makacha indicated that there was heavy rain during the hike to Lava Tower.

We have learned that 2 porters have also tragically died in recent days. At the moment it is unclear whether lightning, hypothermia, or another cause was responsible; condolences to the families of all 3 victims.

Lightning is not common on Kilimanjaro itself (e.g., zoom in with this Google Earth overlay showing lightning frequency), and deaths are quite rare - especially considering the number of people camped high on the mountain most nights . An article in the Tanzanian "Daily News Online Edition" recalls the previous incident in 1999, which occurred just a couple months before we began working on the mountain. The article quotes a National Park source suggesting the terrible idea that climbers take cover in caves (above 4,000 m) during rain, evidently not aware that the 1999 death occurred at Shira Caves, a short distance from where the death occurred this week.

While strikes may be infrequent, lightning is often visible at night from high on Kilimanjaro, and thunder has been heard while camped at the summit for fieldwork on the past two trips.

Can we learn anything from summit weather on 2 January that may help explain the tragic death(s)? Maybe. Wind direction on the Northern Ice Field blew steadily from the South beginning about midnight, at a bit lower speed than normal for the day. Southerly flow is relatively uncommon at our measurement site; wind is more typically from the East, which helps suppress convection above the mountain's western slopes (up which many climbers ascend). It is possible that light winds from the south, in conjunction with regional instability, aided the development of convection which led to the lightning strike.

On 4 January humidity decreased dramatically, the wind veered back to the East, and solar radiation measurements indicate generally clear conditions.

No comments:

Post a Comment