Authored by Doug Hardy of the Climate System Research Center at the University of Massachusetts, the following blog posts covering the March snowfall on Kilimanjaro’s glaciers were originally published on Kiboice on March 14 and 30, 2018. Kiboice is dedicated to sharing news and stories on Kilimanjaro’s summit glaciers and climate.
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 to 30 cm of continuous ablation during February. A context for the event follows.
Figure 1 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, snow cover 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 snow cover 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 three 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 four 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 snow cover 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.
In Figure 3, 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 the output from the numerical model.
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.
The previous paragraphs provide 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 the acquisition of useful satellite imagery from above.
As March comes to a close, telemetry is working well again (with thanks to Mike Rawlins at the University of Massachusetts Climate Center for help on this). We now know that net snow accumulation for the first three 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 five days later provides a clearer depiction of summit snow cover (below; centered further east than the 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. Snow cover 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 4,750 m— which is 1000 m below the caldera rim.]