Dry July

Preliminary data show July 2013 to be the driest month on record for the Northern Ice Field, as measured by relative humidity via telemetry (2004-2012). July and August are typically the driest months at the summit, with July relative humidity (RH) averaging 42 +/-4% (1 std. dev.), so last month's mean of 25% was clearly anomalous. Measurements varied by only ~1% between two sensors in two different radiation shields, aspirated and naturally-ventilated. We expect verification of these values upon the next station visit, when 5-minute data from the high-accuracy, CRN-compatible shield will be recovered.

July ablation at the AWS was only ~8 cm. No snowfall, very low humidity and slightly above-average wind speed during the month would all promote sublimation, and thus ablation closer to the 10-year average for July of 11.3 cm might be expected. One explanation for below-average ablation could be that residual snowcover remains from the 2012-13 wet seasons. If so, telemetry suggests that there cannot be much snow/superimposed ice left - and once older, bare glacier ice is exposed, ablation will likely increase dramatically. Re-positioning of the AWS tower may be necessary in October, for the first time in 2 years.

Meager long rains

Snowfall at the summit during the "long rains" season was unusually meager this year. For March through May, net accumulation amounted to only 20 cm, or less than 1/3 of that last year. The most prolonged period of accumulation occurred between mid-March and mid-April (~23 cm), some of which settled and ablated rather quickly afterward. The first half of May brought ~13 cm of additional snow, a period during which there were "crazy, torrential rains" in Moshi. Little additional accumulation has been recorded at the summit since mid-May.

So, based on preliminary data, snowfall during the month of December was roughly of the same magnitude as that for the entire "long rains" period March/April/May 2013.  The stage could be set for considerable ablation during the forthcoming, extended dry season...

Good read

Anyone with an interest in "animals, adventure and discovery in the wild places of Africa" will enjoy reading Alan Root's memoir Ivory, Apes and Peacocks. The book was published last year in London by Chatto & Windus, an imprint of Random House Group Limited (UK), and although not yet available in America it is easily available from English booksellers.

One of many fascinating stories in the book details the flight Alan made with his wife Joan over Kilimanjaro. Root does not specify a date for the flight, which based on other information was likely 10 March 1974. Launching from the eastern flank, they flew as high as 7,500 meters. He writes that "we gazed down from our gossamer craft as the dome of Kibo, the highest point in Africa, slid slowly by -- almost a mile below us."

Then, as today, Root notes that "any snow falling on it soon melts." The image above with the balloon shows the incipient hole developing in the Northern Ice Field, which Hastenrath & Geischar observed on a 1989 Landsat scene and discuss in their 1997 Journal of Glaciology paper. Enlargement of the hole eventually split the ice cap into two parts last year (2012).

Once past Kibo they started dropping towards the Shira plateau and encountered a dead spot where "the balloon came slowly to a halt." Evidently they were in a zone of converging horizontal airflow, coming around both sides of the mountain, and before afternoon convection was well developed.

Root landed the balloon in Moshi. As might easily happen today upon such a landing, they "were quickly surrounded by a crowd of curious and laughing Africans". Less likely to happen today, fortunately, Alan next heard automatic weapons being cocked. Along with his wife and ground crew, they were arrested, accused of spying, and hauled off to the Moshi police station for 2 days of interrogation.

This is the only portion of the book pertaining to Kilimanjaro, yet every page offers fascinating observations and accounts of his African experience. Numerous reviews have been written on the book; here is one from The Economist.

Delay in telemetry processing

[UPDATE 2 Apr. 13:30 GMT]  The 2 recent images above are offered as consolation for the delay in posting the monthly weather summary. Both views are from Moshi, looking up 5,000 m to the summit. The upper photo with early-morning light is from 22 March, with new snow down to perhaps 4,500 m elevation. The lower image was taken yesterday evening.

Typically in the first few days of each month, we post a synopsis of the previous month's weather at the summit (here). For March, the summary will be delayed by a week or so due travel by our data manager.

Widespread rain is being reported from Tanzania, so check back next week to learn how much snowfall the summit glaciers are receiving!

long-duration climate observations

PNAS recently published an important opinion piece by Carl Wunsch et al. that is well worth a read. It is freely available in HTML and PDF format from the Academy website, and less than a page and a half in length. They argue convincingly that "understanding of climate change is a problem for multiple generations" - stressing that an increased emphasis must be placed on long-duration observations of the climate system.

My favorite sentence takes nothing away from the value of modeling, yet emphasizes their key point:  "Today's climate models will likely prove of little interest in 100 years. But adequately sampled, carefully calibrated, quality controlled, and archived data for key elements of the climate system will be useful indefinitely."

Wunsch et al. point out numerous obstacles to obtaining adequate observations, lamenting that "governments have not done well in sustaining long-term observations." Some of us are all too familiar with this problem, yet this is not universally the case. One of NOAA's most far-sighted undertakings - the U.S. Climate Reference Network - has just achieved a decade of operation, thanks to staff and managers at NOAA whose vision has been laser-sharp. A paper reviewing this program is about to be published by the American Meteorological Society, and available here now.

The USCRN program can be a model for measurements of other climate system elements, domestically and internationally. Broadly implementing the USCRN approach would be an excellent way to address the intergenerational problem highlighted by Wunsch et al.

New aerial images

During the Wings of Kilimanjaro (WoK) expedition in early February, a helicopter flew to the summit with supplies for the group. The pilot was Ben Simpson of Tropic Air, a company based at the foot of Mt. Kenya and experienced in carrying out rescues there. Tropic Air uses the French-made Eurocopter AS 350 B3, from which WoK videographer Anika Craney got some great footage. A 12.5-minute clip of the flight is posted on the WoK FaceBook page, available here.

The following captures are from Anika's video, posted here to provide an update on recession of the glaciers; several of the perspectives she obtained are quite unique.

Below is the less-commonly seen half of the Northern Ice Field, with the eastern edge at left. The crater is behind the upper ice as seen here. Despite extensive snowcover (for early February) the split between the two halves is clearly visible; this did not exist and/or was not known prior to ~1989.

At the bottom edge of the image below is Stella Point. Trails to both the summit and crater camp are visible. The eastern end of the Rebmann Glacier is in the foreground. The apparent "hole" was recently observed on satellite imagery, and may have developed due to anomalous geothermal heat flux. Alternatively, it may have begun as a supraglacial pond which enhanced shortwave radiation receipt.

Fragments of the Southern Ice Field are seen in the next image. Beginning on the right-hand side, the Rebmann Glacier used to extend downslope but is primarily confined to the crater rim these days. Although partially obscured by cloud, this view provides a context for the image above. The narrow Decken Glacier becomes thinner each year, and may soon be cut off from the ice above. The largest ice body remaining is the Kersten Glacier, which is also seen in the fourth image. Within the past couple years the Kersten has become detached both from ice above and from the Decken Glacier to the right. Lastly, the Heim Glacier is the small sun-lit body of ice beyond the lower Kersten. As recently as 10 years ago the upper portion of this glacier began not far below the crater rim.  

Below is detail of the view above, showing how the Kersten Glacier has fragmented from the Decken, and into an upper and lower portion. Uhuru Peak is the high point behind the upper section and obscured by cloud in this view.

Many thanks to WoK and Anika for posting this video!

Windy [UPDATED 12 Feb.]

[UPDATE 12 Feb. 18:00 GMT] A final update to the weather graphic has been posted below (or here). Wind speeds and direction have returned to more typical, seasonal values. It was ironically the interval 3-6 February with anomalously high wind speeds, while the expedition was at the summit and prepared to fly off. Was early February a good time of year for the flight? Certainly; the longterm mean values shown in plots A and B both demonstrate that - on average - conditions at the summit at this time are very reasonable for paragliding. But, as we have learned in our decade of measurements, the interannual variability of climate on Kilimanjaro is large -- and summit weather can never be taken for granted.

[UPDATE 7 Feb. 04:00 GMT] Telemetry data from the summit as of midnight Wednesday local time have been added to the graphic below. Late yesterday the wind speed dropped, and Thursday is beginning with winds steadily from the East at a more reasonable speed of 8 m/s. However, humidity was high through the day Wednesday and approaching saturation at midnight. Note how little snow ablation occured (plot C). Looking forward, the forecasting models show a strong gradient in 500 hPa-level humidity parallel to the Tanzania-Kenya border, so exactly how the pattern becomes established may determine if tomorrow (Thursday) is flyable. Lets hope for the best.

Previously:  at 9 AM Tuesday morning, the image above shows how Kibo appeared from Moshi (courtesy my friend Simon at Summit Expeditions:  website and FaceBook). Such great clarity is the result of strong easterly wind. Very strong. Too strong for paragliding.

Check the graphic below to see a context for wind speeds since Sunday; plotted values have been updated to 8 AM local time this morning. In quantitative terms, the 4-hourly wind speed for the period 20:00 - 24:00 last night was 18.4 m/s = 36 knots = 41 mi/hr = 66 km/hr. This is more than 2 standard deviations greater than the longterm mean for this time and date, and as discussed in the 1 Feb. entry below, wind speeds over shorter intervals (e.g., 1-min average) have almost certainly been much greater. Furthermore, this 4-hourly speed equals the highest 4-hourly February value we have recorded on the glacier, which occurred 8 February 2004 (8 AM to 12 PM).

The forecast does indicate lessening wind speed, although it may be another day or two. To clarify yesterday's post concerning wind speed decreasing through the morning, this is the generalized diurnal pattern on Kilimanjaro, not a forecast. Nonetheless, the NOAA Climate Prediction Center forecast for the Kibo grid cell shows decreasing wind speeds at 500 hPa in the hours ahead. Lets hope so, for those seeking to fly down.

Lastly, this nice image from Moshi clearly shows the glacier changes mentioned in the previous post. Ice extent today is quite different from that of 10 years ago shown on the Wings of Kilimanjaro FlyTrace map.