Long Rains 2014

The most-important wet season for Northern Tanzania - "Masika" or "Long Rains" - typically occurs within the 3-month interval of March through May (MAM). Although a distinct element of regional climate, there is considerable year-to-year variability in both timing and magnitude. On Kilimanjaro, the weather is wet during the Long Rains and few organized groups are on the mountain. The Long Rains are generally coincident with the period of greatest snow accumulation each year.

The plot below shows a proxy measure of recent snowfall at the summit, in the form of daily change in glacier surface height; increases in height are due snowfall or redistribution, and decreases are due to combined processes of ablation. For the 2014 Long Rains, the net change in height based on calendar months MAM is a mere 10 cm. However, based on a preliminary, more-meaningful total of daily snowfall amounts, 2014 is not much below normal -- probably due to several intervals without snowfall (i.e., height decrease) and little new snow after ~8 May (red star in figure).

Most interesting for 2014 snowfall to date is the big February event, specifically the 3 days (8-10) when the net height increase was over 20 cm. The month of February often encompasses a mini dry season, yet not with regional circulation as shown below, when airflow at summit level is out of the Congo Basin! (Flowlines are in yellow; note Lake Victoria at top left, skinny Lake Tanganyika at left, and the island Zanzibar to the right of the date label; winds at the summit AWS are almost always from the East.) For additional discussion of this snowfall event, occurring during considerable cyclonic activity in the south-west Indian Ocean, see the entry for 20 February 2014. Relatively meager precipitation through the entire Long Rains season demonstrates the potential importance of Indian Ocean cyclones to the glaciers of Kilimanjaro.

Dry season begins

The long rains are ending in the Kilimanjaro region. Here is the mountain last Saturday, courtesy of Simon Mtuy at SENE. An update on snow fall at the summit during the long rains will be posted this week.

Climate measurements on the Roof of Africa [updated]

Several radiometers used on Kilimanjaro AWS are made by the Dutch company Kipp & Zonen. Coincidentally, they were all transported to Tanzania aboard Royal Dutch Airlines (KLM).

The Kipp & Zonen website has just published an overview on Kilimanjaro, our climate studies, and why it is such a great place for climate research. The article contains several images and discussion of the following plot. Intrigued? Check it out here.

[UPDATE 5/5: A more-detailed version of this overview appears in the April edition of Meteorological Technology International - a very interesting trade publication. A link to just the 4-page article with photos is available here.]

(This is blog post #100!)

Unsettled weather continues

Kilimanjaro was visible from Moshi this morning, for the first time in awhile, following heavy rain last night. This has been a wet month on the mountain! Thanks to Simon Mtuy for sending the image and report.

Rain, snow & cyclones [updated]

For several years now, I have corresponded with Timba at Ahsante Tours & Safaris about a relationship between Kilimanjaro-region precipitation and cyclones in the south-west Indian Ocean. On Monday afternoon (10 Feb.) he wrote that it was "currently raining big time here, and has been for the past weekend".

So, here is a synopsis of what was happening in the ocean. Tropical Storm Edilson had developed by 5 Feb. Another Tropical Depression formed on the 6th, which became Tropical Storm Forbane on 8 Feb. This quickly developed from Moderate to Severe that day, by which time Edilson was rapidly moving south. Fobane became subtropical by the 10th, and also moved west. Here is a map of the storm's positions on the afternoon of 8 Feb., from the Severe Weather Information Center of the WMO (World Meteorological Organization):

At the summit of Kilimanjaro, snow accumulation was considerable over the weekend (8 & 9 Feb.). Measurable accumulation also occurred in the days prior, particularly 4 Feb. The graph below shows daily snow accumulation on the summit glaciers, with our data currently extending only until noon on 10 February.

Here is a beautiful map of regional circulation at 500 hPa (summit level) from Earth, based on NOAA data. This is a screenshot showing the situation at 15:00 local time on 8 Feb., with winds from 315° at 21 km/hr (5.9 m/s) at Kilimanjaro level (indicated by the small green circle). Data sent by telemetry from the AWS correspond remarkably well with this NCEP value, averaging 6.3 m/s from 334° for the period noon to 16:00 local time.

A snowfall total of ~20 cm through 9 Feb. is an important event at the arid summit of Kilimanjaro. This time of year is more typically associated with a brief dry interval, while the ITCZ is north of the mountain. It is probably a safe hypothesis that this - and similar snowfall events - are not associated with either the short- or long-rain seasons. Nonetheless, they are tied to regional atmospheric circulation and activity in the south-west Indian Ocean. They are very important in terms of mass balance for the glaciers, and are also to the safety and success of porters, guides, and clients on the mountain. Lastly, with further analysis the impacts of cyclones at this time of year should be relatively easy to forecast. Thanks again, Timba!

[UPDATE 2/12: Simon Mtuy of Summit Expeditions (SENE) wrote that his group was within the caldera ("Crater Camp") on the night of 8 or 9 February. As is sometimes the case, the amount of snowfall appears to have been greater within the crater than on the glacier. He writes "they have huge snow through the night, and the tents were about 1 m under the snow." To reach the summit they had to cross the crater to Stella Point and then follow the ridge to Uhuru Peak, rather than ascend directly from camp. In the text above I mention that unexpected snowfall has consequences for both humans and the glaciers. Simon writes that this event created big problems for the porters, who weren't expecting snowfall and either did not have sunglasses or had some which provided inadequate protection against the highly-reflective new snowcover.]

Short-rains synopsis

On the Northern Ice Field the 2013 "short rains" were right on schedule, with snow accumulation beginning ~5 November and continuing intermittently until ~17 December. Net accumulation of snow at the weather station was 49 cm, which is more than the glaciers typically receive during this seasonal wet period. Settling, transformation and ablation of this snow in the month following (i.e., to mid-January) lowered the surface by ~16 cm. Nonetheless, through the mini dry season before the "long rains" begin in March (typically) the glacier surface will remain relatively bright, causing much less energy absorption than that following years when the "short rains" are meager or fail altogether.

The two sets of Landsat 8 images below depict the regional- and local-scale impacts of the "short rains". In the top set (click to enlarge), Kibo caldera can be located as the small blue area (i.e., ice and snow) just below and to the right of image center; resolution in both cases is 30 m. The first scene (30 October) was acquired shortly after our fieldwork, when virtually no seasonal snow was present at the summit (thin, high clouds partially blur the image slightly). There is little snow within the caldera in the middle scene, although remnants of the snowfall mentioned in an earlier post can be seen. In the 18 January 2014 scene, considerable snowcover can be seen in the caldera and on the flanks of Kibo - even though the short rains ended in mid-December at the summit; perhaps they continued longer at lower elevations. Finally, note the progressive response of vegetation around the mountain to short rains precipitation; an ephemeral lake is visible to the north of Kilimanjaro on 18 January.

The following images are cropped from the full Landsat scenes, providing greater detail of Kibo and the caldera (click to enlarge).

And yet more snow!

More fresh snow on Kibo this morning, after "big rains" last night in Mbahe (near Marangu gate). Thanks to Simon at SENE... better than any webcam!