Friday, March 6, 2015

Tropical Cyclone 15S [updated]

Tropical Cyclone 15S is currently in the Mozambique Channel, as shown by the image above from NASA's Terra satellite processed by the NASA Goddard MODIS Rapid Response Team. The image was acquired at 10:40 East Africa Time on March 6th.

Will the circulation associated with 15S influence Kilimanjaro snowfall? We will be keeping an eye on this, for the circulation around prior cyclones seems to have been associated with precipitation at this time of year - as moisture is delivered from the Congo Basin. Here is a previous discussion, initiated by conversations with Timba at Ahsante Tours & Safaris.

Forecasters at the Joint Typhoon Warning Center anticipate 15S wind speeds to increase over the next few days. The duration that the cyclone remains over warm water may determine the impact on Kilimanjaro. We will provide an update next week!

 [UPDATE 3/11:  No apparent influence this time. Mid-tropospheric circulation to the north (i.e., Kilimanjaro) seems not to have been substantially influenced by 15S, and westerly flow never developed. We'll keep an eye on future cyclones this season.]

Wednesday, March 4, 2015

February snow

February on Kilimanjaro is typically a rather dry month, a mini dry season sandwiched between the short-rains of roughly November-December, and the long-rains during the March-April-May period. Last month followed this pattern, excepting a brief, important event occurring mid-month.

At the summit, snowfall began late on the 14th and appears to have continued all day on the 15th. The 16th may have been dry in the morning, but by evening telemetry data suggest that snowfall began again, with increased wind speed that may have caused drifting of the fresh snow. Reports from climbers on the mountain mention heavy snowfall at Arrow Glacier Camp and in the Western Breach. By early on the 18th the event was over and dry conditions again prevailed on into early March.

This February event is important because it was the largest snowfall event since the long-rains of 2014, totaling 16.5 cm. This is ~2 cm greater than the event of late-November into early-December 2014. Although events of this magnitude pale in comparison with those on other mountains, they must be viewed in context; the summit of Kilimanjaro is very dry. Snowfall on the summit glaciers adds mass to horizontal surfaces, and more importantly - a bright, smooth snow surface changes the energy balance both on the glaciers and on surrounding caldera surfaces adjacent to the vertical walls.

Tuesday, January 13, 2015

Short Rains update - January

Above is a new view of the mountain from Simon Mtuy at SENE, taken early on the morning of 7 January. The snowline is at about the same elevation as earlier, and although difficult to judge due to the steep slopes, snowcover on the mountain appears to have increased. Based on telemetry, the timing of snowfall on the Northern Ice Field during the Short Rains has been rather irregular, with an initial event in late September into early October, a minor event in mid-October followed by about a month without accumulation, and a minor event towards the end of November. The largest snowfall event occurred early in December, followed by minor accumulation at Christmas. Snowfall from the event depicted above was one of the season's largest events, so far...

Thursday, December 4, 2014

Short Rains underway [updated]

Thanks to Simon Mtuy at SENE for this beautiful snowy view of Kibo, taken early in the morning of 29 November. Note the sharp snowline at ~4,500 m!

[UPDATE 12/5: Below is a clear view of the mountain taken this morning at 8 AM, again courtesy of Simon Mtuy. Some of last weeks snow on rocky surfaces has sublimated / melted, but there probably hasn't been much ablation on the glaciers. This image depicts the continuing break-up of the former Southern Ice Field, showing how the Kersten and Decken Glaciers have split from the upper-most ice. Another recent view of this - from Mweka - can be seen in an exceptionally-clear photo by Phil Stouffer on his Flickr page here.]

Thursday, October 9, 2014

September Fieldwork

We spent 4 days in September at the Kibo AWS and on summit glaciers. Details and photos of the fieldwork will be posted in early November, as additional fieldwork elsewhere is underway until then.
A preview of our findings is provided by the image above, taken during an afternoon snow squall. These were real snowflakes, rather than the more-typical dry-season graupel. Two days earlier during our ascent to the crater, our windward sides became 'plastered' with rime. Snowfall that day and into the night left a thin blanket even below Lava Tower - to perhaps 4,400 m - and this endured for more than 24 hours. The dry to wet season transition was underway.

Comparison of this image with those from October 2013 (4th image here) shows a positive mass balance at the AWS site - which of course is why the glacier surface albedo here is so high. Snow accumulation near the AWS varied slightly according to our network of ablation stakes, yet we documented considerable variability at a larger scale; to the east we found one location with more than 1 m of residual seasonal snow, yet mass balance was decidedly negative on the Furtwängler and south-side glaciers.

Also to be discussed in greater detail is new evidence for sub-glacial melting!

Monday, June 30, 2014

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.

Monday, June 2, 2014

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.