Wednesday, September 5, 2018

Seasonal snowcover change

Two views of Kibo from the plains below reveal that snowcover has largely ablated from the mountain's slopes. From the northeast (upper image) dry slopes appear capped by a fringe of snow on the crater rim, while the Northern Icefield is visible in the second image.

Both images above were taken during the 2018 Kilimanjaro Stage Run, a wonderful way to experience the mountain and the diverse cultures residing on the flanks. Adventurous runners of all abilities should look into this fun event!

Below is another view of snow on the mountain, acquired one week later. Nearly complete snowcover remains within the summit crater, although it appears that the trail to Uhuru Peak is now free of snow. Lower on the mountain, trails and camps are visible in this European Space Agency image.

Despite the extent of snow within the crater, telemetry of measurements from the Northern Icefield indicate that the glacier surface lowered by 15-20 cm, likely due to sublimation, melting, and compression of long-rain snow. This snow benefits glacier mass balance by adding mass and reducing energy exchange (e.g., reflection of solar radiation) - briefly reducing the glacier recession rate.

Monday, July 16, 2018

Kibo summit snow


In mid-July, Kibo remains almost entirely snow covered at high elevations. The image above depicts this snowcover along the crater rim on 10 July, looking toward Uhuru Peak with the upper Deckens Glacier on the left. Snowdepth varies considerably in mountainous terrain, due to both snowfall and ablation processes, yet nearly one meter of snow remains on the Northern Icefield (0.98 m). This represents net accumulation since the beginning of March. Relative to the glacier surface in early October - when we visited for fieldwork - the net increase in surface height is 0.72 m.

Additional detail on Kibo snow is provided by the images below. The first is a Sentinel-2 image from 13 July, with uniform snowcover in the crater and extending down all slopes. Note some thinning and emergence of bare spots in the past few weeks (see earlier posts). Below the satellite image is one from just below Stella Point, showing the depth of accumulation on 10 July. The final image also looks toward Uhuru Peak (with 40+ people), across the Furtwängler Glacier, and towards the Northern Icefield; penitentes in the foreground typically develop in deeper snow at this time of year, due to sublimation. They will likely keep growing for the next couple months.

Many thanks to our friend Timba in Moshi for providing these images!

Friday, July 6, 2018

Kibo remains snowy, as illustrated by the Sentinel-2 image above from 3 July. Over the past month, the snowline has been only slowly moving up the mountain. Accumulation at high elevation and within the crater has been ablating slightly; compare the image above with those in earlier postings.

Extensive snowcover on the glaciers and surrounding slopes is keeping the albedo high, minimizing mass loss... at least for the moment.

Kilimanjaro is not alone in being unseasonally snowy in recent months. For example, in the Karakoram Mountains (Pakistan) climbing teams on mountains such as K2 are finding dangerous avalanche conditions due to heavy snowfall, during the core climbing season. More details can be found here.

Quelccaya Ice Cap and the Cordillera Vilcanota in Peru are also unusually snowy for July, the result of La Niña accumulation during the wet season (esp. DJF) and atypical dry-season snowfall in the past couple months.

In Northeast Greenland, the winter of 2018 brought twice as much snow as the long-term average, and snowcover into early July remains so extensive that Sanderlings and other shorebirds may not even attempt nesting this year. The late snow is having large consequences for the ecosystem.

Finally, snow on portions of the Greenland Ice Sheet is resulting in the "least surface ice loss in decades". As Jason Box notes via Twitter (@climate_ice), these persistent extremes in patterns of atmospheric circulation are an expected signature of climate change.

Wednesday, June 6, 2018

Dry season begins

One of the most-reliable aspects of Kibo summit climate is when the extended dry season begins; typically between late May and early June. Despite considerable snow accumulation through 2018 long rains (see posts below), the dry season initiation this year appears to be right "on schedule".

Above is a view of Kibo from Moshi just after 7 am on 28 May (Simon Mtuy credit), after a long period in which the mountain was shrouded in clouds. Snowcover has changed little since March.

The timelapse below includes images every 5 days for the past month, from ESA Sentinel-2 L1C data. Note the decreasing cloud cover thickness and extent, and thinning of snowcover on the mountain flanks. Telemetry of measurements from the summit reveals little change in snowdepth on the Northern Icefield through the interval.

In the months ahead, all seasonal snow will likely sublimate and melt, exposing glacier ice to radiant and turbulent energy. Without the bright, protective snowcover, the area and thickness of the glaciers will continue to diminish.

Tuesday, May 15, 2018

Snowcover update

Ablation has dominated over accumulation on Kibo recently, yet the mountain remains snowy. On a Sentinel-2 image from yesterday (above), note the rising snowline and thinner snowcover on ridges and east-facing slopes - relative to images posted previously. With minimal clouds over the summit caldera, the Northern Icefield margin can now be distinguished, just to the northeast of the Reusch Crater (outer circular feature).

Below are some images contributed by Adam Quenneville, from his visit to the summit on ~26 April. The panorama looks south over the upper Kersten Glacier from near Uhuru Peak. Note how the windblown and frozen snow surface allowed climbers to walk without breaking through. The middle image shows the Northern Icefield (upper left) and the Furtwängler Glacier margin - including the tiny remaining eastern fragment. Adam's team is shown at Crater Camp in the lowest image, with the Furtwängler and Northern Icefield in the near and far background, respectively.

Friday, March 30, 2018

More March snow! [updated x3]

Numerous reports of snowfall on the mountain have been received this month, which in some cases has prevented groups from reaching the summit. While the long rains often begin during March, snowfall this month appears to be somewhat exceptional.

The previous post provides information on early March snowfall. Further details have only recently emerged, because snow on one of the solar panels prevented satellite transmissions for ~5 days during the middle of the month, and then again on 20 March. During this time, extensive cloud cover also prevented acquisition of useful satellite imagery from above.

As March comes to a close, telemetry is working well again (with thanks to Mike Rawlins at UMass Climate System Research Center for help on this). We now know that net snow accumulation for the first 3 weeks of March amounted to 63 cm on the Northern Icefield. As the ESA Sentinel-2 image above shows, snow blankets the entire summit caldera and upper slopes of the mountain (look closely, to discriminate snow from stratus fractus clouds). This is the greatest snow accumulation on the glacier in years -- with additional snowfall likely during the remaining months of the long rains (typically March through May).

For those climbing the mountain in the months ahead, fear not. Snow on the routes will quickly compact and you will have a chance to experience conditions more typical of past decades. Dust will be minimal, beautiful nieve penitentes will grow as the dry season progresses, and you will encounter much happier glaciers. It is also important to keep in mind that this accumulation is surely temporary, and will not change the reality that these glaciers are disappearing rapidly.

[UPDATE 04/02: Another Sentinal-2 image acquired 5 days later provides a clearer depiction of summit snowcover (below; centered further east than image above). Some ablation has taken place, allowing recognition of the caldera rim as well as that of the Reusch Crater and the inner Ash Pit. Snowcover remains sufficiently thick that snow and ice cannot be distinguished at this resolution. We can now see a sharp transient snowline on the west side, at approximately 4750 m - which is 1000 m below the caldera rim.]

[UPDATE 04/10: Sentinel-2 acquired a beautiful snowy image yesterday, with little cloud cover. The GIF below shows 4 registered images, including yesterday's (9 April), one from 5 days earlier, and two from late March. The red circle in the northwest corner is at ~4,700 m, while that in the southeast corner is at ~4,800 m. (Barafu Camp and adjacent trails can be seen just south of the lower red circle.) Although the transient snowline can be seen rising slightly during this period of ~2 weeks, the summit remains entirely snow covered.]

[UPDATE 04/11: Very clear view of Kibo from Moshi this morning, verifying the pattern and magnitude of snowcover seen in the 9 April image above. Thanks to Simon at SENE for the update!]

Wednesday, March 14, 2018

March snow

The first week of March brought a net snow accumulation of nearly 50 cm to the Northern Icefield, which by any measure is a snowy interval on Kilimanjaro. This precipitation follows 25-30 cm of continuous ablation during February, as illustrated in the previous post. A context for the event follows.

Figure 1 (below) shows Sentinel-2 satellite images of the exact same scene, on the last day of February and on 5 March. As detailed in another post, snowcover was primarily confined to steep north-facing slopes by the end of February. Although considerable cloud cover is present around the mountain on the 28 Feb. image, the summit caldera is mostly cloud free. Note the red squares, which are co-located on the 5 March image for orientation. High clouds partially obscure the March image, yet pervasive snowcover is visible. A sharp snowline at ~4,400 m is visible on the left-hand side of the image.

Figure 2 provides two snowy views of the mountain from the Moshi area (SENE credit). Despite low resolution of the 3 March image (upper), substantial snowfall obviously occurred since the satellite image acquired 3 days earlier. Snowcover appears to be somewhat more uniform than it was on 8 March (lower) - consistent with the timing and magnitude of snowfall recorded at the summit weather station.

At the Northern Icefield, satellite telemetry (Argos) shows ~12 cm of accumulation on 2 March, ~15 cm on the 3rd, and ~5 cm on each of the next 4 days. The precision of these daily totals will be improved when higher temporal resolution data are recovered from the automated weather station. Due to the diurnal cycle of climate on the mountain, some ablation likely also occurred on most of these days and is probably responsible for the patchier snowcover on the 8 March image.

A fascinating element of this snowfall period is provided by a depiction of regional-scale circulation (Fig. 3; Cameron Beccario credit). Here, airflow on the morning of 4 March is illustrated at the 500 hPa pressure level, equivalent to Kilimanjaro summit elevation. Airflow at this level appears to have been influenced by Tropical Cyclone Dumazile beginning on the 2nd as the storm intensified, continuing through about 7 March. The relationship between Kilimanjaro snowfall and cyclones in the southwest Indian Ocean is being investigated with collaborators Thomas Mölg and Emily Collier (Friedrich-Alexander University), along with Timba Nimrod.

On this figure, Kilimanjaro's location is shown by the green circle. Note the westerly wind, which prevailed through the snowy interval. Wind measurements at the summit (via telemetry) verify this airflow, which is atypical at the summit (only ~5% of hourly means are from 270° ±30°). Riming of the instruments appears to have occurred during the event, causing data loss particularly on the 3rd, 4th, and 6th. Nonetheless, such verification of airflow by in situ measurements is not a trivial finding - for very few continuous meteorological measurements exist from nearly 6000 m with which to compare output from numerical models.

Finally, figure 4 depicts circulation and humidity on 3 March. Here the highest humidity is shown in cyan color, suggesting a Congo basin origin for this precipitation event.