Friday, February 28, 2014

Mean daily air temperature [updated]


Here is the annual cycle of air temperature at Quelccaya (5,680 m), based upon the best dataset available. Each mean daily value is based upon ~4 years of measurements, which are not contiguous due to a power problem in 2010-12; the record has been smoothed slightly for clarity. A previous post (available here) provides some background, and the data will be available here shortly.

Analyses of these and other Quelccaya data are gearing up, working towards publication of a Quelccaya climatology. As illustrated by this graph, some interesting patterns are emerging.

[UPDATE 3/25:  A complete record of quality-controlled hourly air temperatures for July 2007-June 2009 are available here, as well as the accompanying metadata.]

Wednesday, January 8, 2014

Heavy snowfall continues

Seasonal snow accumulation started early, and was considerably above normal by the end of November, as illustrated in a post last month. This pattern has continued through December, with 76 cm of net accumulation for the month, and snowfall to date for 2013-14 continues to be the highest of our period of record (since 2004). On January first, snow depth at the station reached 1.5 meters, twice the average for this date!

Despite all the snow this season, note how little snowcover blankets the landscape on the 29 December Landsat 8 image below. This cropped scene is essentially the same as that posted earlier, for 26 October and 11 November, revealing almost no snow below ~5,200 m. However, the impact of this precipitation on vegetation is discernible as more-intense shades of green.

Snowfall this season has resulted in weak transmissions to the GOES satellite, and only ~11 percent of data from the station was received by telemetry during December. Rime formation on the antenna may also be degrading the signal, something our timelapse camera is hopefully documenting. Fortunately, all measurements are stored on-site and will be recovered during 2014 fieldwork.


Friday, December 20, 2013

Air temperature series [updated]!

In June of 2007 the Quelccaya AWS was supplemented by instrumentation compatible with NOAA’s Climate Reference Network (CRN). As nicely documented on the CRN website, several highly-accurate air temperature sensors housed within a continuously-ventilated radiation shield provide what is likely the best air temperature measurement possible in the extreme environment of the ice cap. (The link above now has comprehensive access to all CRN publications.)

Further information on Quelccaya temperature measurements is available here, along with access to the first 3 years of measurements.

Processing of the full 2007-13 temperature record from these sensors has just been completed, and access will be provided early next month. This record was assembled from 5-min averages based on 3-4 PRT sensors, quality controlled following CRN protocols (see Palecki & Groisman,

UPDATE 3/25:  A complete record of quality-controlled hourly air temperatures for July 2007-June 2009 are available here, as well as the accompanying metadata. The full 2007-13 period has been processed, yet these are not yet available due to insufficient fan speed during early-morning hours through a portion of this period. Maximum daily temperatures were largely unaffected and this series will be available soon. Thanks for your patience.]




Saturday, December 7, 2013

Snowy Vilcanota


This is the most extensive snowcover I've seen on a Landsat image of the Quelccaya area. Looking through a layer of thin clouds, Sibinacocha is barely visible in the upper left; the yellow circle tightly circumscribes the ice cap, which isn't visible here. This image was acquired on 26 October.

A context for the event is provided by snowfall telemetry from the summit AWS, via GOES telemetry. The figure below shows daily snow surface height at the station, with each year in a different color. The lowest horizontal dotted line is the zero reference, or the lowest height reached each year (defined here as June-May), and the upper horizontal line is 1 meter of accumulation. Accumulation for 2013-14 is shown in white, depicting a fairly-average surface height minimum date in early October. The snowfall event captured in the Landsat image occurred during the straight, steep increase in the white line, and accumulation by month's end was 2-3 times the mean (or median) since 2004. [Note that the straightness of the line for 8 days cannot be taken to indicate linear accumulation. Rather, heavy snowfall resulted in weak transmissions and intermittent loss of telemetry.]


Below is another Cordillera Vilcanota scene, this one acquired 11 November 2013 by Landsat 8, after the snowfall event (Landsat Scene Identifier:  LC80030702013315LGN00). Snowcover off the glaciers is somewhat diminished, because higher air temperature and increased clouds make this time of year warmer - and snow melts. Snowcover shown here is primarily at elevations above ~5,000 m. Compare this with the seasonal cycle for 1998 depicted in the right-hand margin of this page, or available here.

Detail of the ice cap and surrounding terrain is shown in the final image, cropped from the same scene.




Thursday, October 10, 2013

Failures, breaks, and solutions

During almost every venture into the field, something inevitably breaks. Try as we may to bring the most appropriate and robust gear with us, and to use it carefully, equipment fails during fieldwork in extreme environments for a variety of reasons: (a) it isn't quite up to what we ask of it, (b) it is simply worn out, and/or (c) it fails due to unforeseen stresses - such as getting dropped.

One of the challenges of gear problems during fieldwork is... solving them! Such tasks span the full spectrum from exasperating to fun, yet their outcomes influence the extent to which fieldwork objectives are met. A few approaches for mitigating gear and equipment failures include: (a) redundancy, in which multiple methods are planned - or equipment brought along - to accomplish the same task, (b) repair, usually requiring supplies and tools, and (c) substitution of a different piece of gear or a different approach.

During fieldwork on Quelccaya in July we were presented with an unusual number of equipment challenges, minor and major, solvable and not. Upon return we pondered, investigated, and resolved them in a variety of ways. Below are our 2013 gear challenges and their solutions or outcomes, in no particular order. In cases where the original manufacturer was contacted, note the variety of support (customer service) we received!
  • After more than a decade of faithful service, a Black Diamond Gemini headlamp must have been damaged during travel, for it was unresponsive when needed the first night at base camp. Neither changing batteries nor disassembling it revealed the problem, which may have been a broken wire within the insulation. A spare headlamp was borrowed from one of our guides, and ironically the Gemini was found on within a duffel late in the trip. The headlamp continues to function fine, but has been replaced and is now relegated to use closer to home.
  • An apparently faulty switch on one of the dual-frequency GPS receivers resulted in loss of some data from one of the base stations. This well-used unit has only LED lights to indicate functionality. Suspecting a potential power problem when the unit was deployed, we bypassed all connections between the GPS and power supply. This initially appeared to solve the problem, which we later learned did not. Although data were lost spanning several days, power was continuous through the most critical period when multiple base stations operated.
  • Continuing with power problems, a "powergorilla" portable power supply station (Powertraveller, Ltd.) came along to supplement aging laptop batteries. Although the unit had worked well on several previous trips within the past 2 years, it appeared dead upon plugging in the laptop. Strangely, it appeared to take a charge just fine via a "solargorilla," yet when disconnected it had no power. Powertraveller was contacted about the problem and agreed to replace the unit, despite expiration of the warranty. A new powergorilla will power a laptop and recharge mobile phone batteries on Kilimanjaro, later this month!
  • At the AWS, three problems developed in the year of autonomous operation. One was the complete failure of the transducer within one of the station's Campbell Scientific SR50 Sonic Ranging Sensors, a relatively uncommon event. These transducers are replaced annually, both to prevent such failures and to yield the cleanest possible measurements; without replacement however, the transducers sometimes last years. When one failed on Quelccaya in mid-May this year, 55 days before our field visit, almost all data were lost. This is why 2 sensors are used on all UMass stations, and replacement sensors with new transducers and desiccant are brought in each year, following careful lab testing. 
  • A second sensor problem at the AWS involved one of the Rotronic MP101A temperature and humidity probes. This was not a new issue and the equipment is not to blame, but is likely due to a combination of the technology used, intermittent ventilation of the radiation shield, and a relatively humid environment during the Quelccaya wet season. The probe which develops problems has been housed within a radiation shield which is intermittently ventilated by fan (2 of every 10 minutes), and under certain conditions ice crystals are hypothesized to grow during ventilation and then melt during the subsequent unventilated 8 minutes. Despite microscopic analysis of several probes by both Rotronic and Vaisala - which clearly reveals damage to the thin-film polymer - the problem with the humidity sensor has never been satisfactorily explained. So, during this field season the probe and shield were both eliminated!
  • The third AWS problem in 2013 was due to the fan motor on the shield referenced above, which allowed measurement of the fan revolutions. This ceased functioning at the end of March. The decision to remove the shield was not difficult, due to known radiation-loading errors with this shield design.
  • A new batch of "harsh-environment" cable ties was purchased for this fieldwork, in an effort to economize on well-proven Tefzel ties. In every attempted installation, the tooth which allows only one-way motion immediately broke; they may have been a defective batch. McMaster-Carr promptly refunded the cost of these.
  • To measure snowpit stratigraphy and sample depth, we have been using a Lufkin brand tape measure with a powerful spring to retract the tape into a housing. When blowing snow accumulated in the pit and buried the tape cartridge, a bit-too-much pulling caused the tape to detach, creating 8 meters of chaos. Replacing the tape was not possible in the field or lab, and an e-mail to Lufkin was unanswered.
  • Lastly, at some point during travel to or from Cusco the airlines broke the frame of a Mountain Hardwear rolling duffel (Juggernaut) - one which had endured numerous prior trips. This has always been a crucial piece of luggage, as it offers more protection for items than a soft duffel and rolls exceptionally well. Mountain Hardwear inspected the break - which was considered unusual - and quickly provided a new Juggernaut.
For forthcoming fieldwork on Kilimanjaro we will be ready for breakages and failures, as always, but we are hoping for considerably fewer than at Quelccaya. After all, there are always other types of gear issues, such as forgetting and loosing things, even though we try to avoid these as well!

Monday, July 22, 2013

Fieldwork!

We are just back from an ambitious program of fieldwork on the ice cap, including 8 days at the summit. The AWS has been raised and serviced, accumulation has been measured, and we succeeded in the GPS survey of motion/ablation stake positions established in 1983 and 1984. Here are a few images from the trip:

Below illustrates the AWS "as found", after digging out the enclosures and raising them. To the right of center is our 2013 snowpit, and the orange flag marks the position of 1983 ice-core drilling done by Lonnie Thompson (Ohio State).

A cold, clear evening at the summit of Quelccaya Ice Cap (2.5 minute exposure).

Our final morning at the AWS with our Perúvian crew from Vicencio Expeditions (left to right:  Koky Casteñeda, Carsten Braun, Theodoro, Eusebio, Felix Vicencio & Doug Hardy; Dave Chadwell not shown).

Base station QSP-2 following 24 hours of high-frequency position measurements.

Position measurement at a (former) stake location near Qori Kalis outlet glacier. 

Friday, June 7, 2013

Final pre-fieldwork accumulation update

During the month of May, snow depth at Quelccaya summit has increased in about half of all years since 2004. By the beginning of June the dry season has typically begun, and until early August, snowfall is only associated with occasional, relatively-brief winter precipitation events.

For the accumulation season 2012-13, snowdepth on 1 June amounted to 1.70 meters, increased slightly by a mid-May snowfall event. This accumulation season is thus second only to 2009-10 (1.64 m) in terms of low snowfall, and considerably below the median 1 June depth of 2.06 m. In contrast, La Niña year 2007-08 saw the greatest snowdepth on 1 June, at 2.40 m.

This update will be the last on accumulation until after our fieldwork, when among other activities we will measure density and determine the water equivalent accumulation for 2012-13. This will provide a more accurate measure of precipitation, and put the accumulation season into a proper longer-term context. Hopefully, we will encounter easy digging!