¡Tanta nieve! So much snow! [updated x2]

The snowy dry season of 2018 continues in the Cordillera Vilcanota. Yesterday's Sentinel-2 image (above) reveals a landscape blanketed by snow above 4500-4700 m. Quelccaya Ice Cap (lower right) is difficult to delineate, suggesting substantial accumulation at the margin. Hopefully our instrumentation continues to record hourly snowfall at the summit.

Note the variation in color of lakes just west of the glacier, surrounding the area of our camp (labeled). This reflects varying suspended sediment input, with relatively high concentrations apparently flowing into the Qori Kalis proglacial lake (north of camp); snow is accumulating, while also melting and delivering sediment to the lakes. The 'double' lake to the northwest of camp (and Sibinacocha) appear dark blue, as upstream wetlands (bofedales) filter sediment from freshly-exposed areas proximal to the glaciers.

We will be in the area during the second half of August, measuring snow and recovering weather station data. Fieldwork will occur later than normal, allowing an assessment of what appears to be an anomalous year. Although this snow will be beneficial to glacier mass balance, the toll on camelids (llama, alpaca) could be severe - without warming solar radiation typical of the dry season.

[UPDATE 7/26: A press release from SENAMHI* earlier this week (23 July) describes snowfall in the preceding 72 hours above 3,800 m in the Andes, accumulating to 20 cm. In conjunction with clouds, they warn of low temperatures and prolonged snowcover reducing food for livestock.

Gustavo Valdivia wrote yesterday learning details of the situation in the Cordillera Vilcanota. He received a call from the Phinaya community president, who described the situation as critical, because a lot of alpacas died in recent days. The local people agree that the weather is very unusual.

Press releases from SENAMHI can be found here (in Spanish), with a machine translation  here. 

*SENAMHI is The National Meteorology and Hydrology Service of Peru or El Servicio Nacional de Meteorología e Hidrología del Perú]

[UPDATE 7/27:  Today I learned from Bronwen Konecky (Washington University) that SENAMHI is making daily meteorological summaries available on their website. The closest station to Quelccaya - and one of their highest - is Sibinacocha, at ~4890 m (labeled on map above). These data show 11 mm of water equivalent precipitation on 21 July, followed by 5.9 on the 22nd. Since this automated station is located at the southern end of the lake, the image above suggests that considerably more snow fell at higher elevations. The regional nature of this event is demonstrated by daily totals from Sicuani (~3600 m, 45 km to the SW); very similar daily totals were recorded.

To access any SENAMHI data in Peru, go here, then use the "Seleccionar" button to select a District; zoom in on the map. Thanks, SENAMHI.]

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.]

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.

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, 2011).

[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.]

A sneak preview of one aspect of the new record is provided above, illustrating how melt energy is far from uniform through the year, or even through the accumulation season. The bar chart shows the number of hours each day in which the hourly mean temperature was above freezing, for each of the 6 years; also shown (as symbols) are the total number of hours above freezing - over 6 years - for each date. Although air temperature rises above freezing during only 0.42% of all hours, the associated melt is having a profound impact on the ice core record!

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.

Preparing for fieldwork!

A component of our forthcoming 2013 fieldwork will involve high-accuracy GPS measurements, uploading data to Scripps for processing, downloading calculated coordinates, and then re-occupying dozens of points comprising a strain net on the glacier which was established and surveyed in 1983. In preparation, Dave Chadwell & Carsten Braun are in San Diego this week testing GPS receivers, a BGAN terminal, laptops, charging systems, and Iridium phones. Multiple redundancies will hopefully insure that things go smoothly on the ice cap!

Snowcover: 2010 and 2013

The previous post compared two Quelccaya satellite images discussed on NASA's Earth Observatory website. Among the many interesting features these show is the transient snowline at the time each image was acquired. Landsat images for any particular location (e.g., Quelccaya) can only be acquired when the operative satellite passes overhead, which has typically been limited to an interval of ~16 days. Useful image frequency is further limited by clouds obscuring the scene. In a recent manuscript submitted to The Cryosphere Discussions, authors Maiana Hanshaw and Bodo Bookhagen tabulate many of the best images that include Quelccaya and the Cordillera Vilcanota, beginning with those from Landsat 2 in 1975.

Our measurements on the ice cap provide a context for the 2010 EO image. The graph below shows how surface height at the summit generally decreases through the dry season. Each year of our measurements is shown in black, and for dry season dates common to all years the mean daily height is blue. Note that height decrease is not linear, which reveals important information about the processes involved!


Also shown (in red) is height through the 2010 dry season, with a pink circle indicating the EO image date. Most of the surface lowering (e.g., ablation) took place after the latest available image that year - and the 2010 dry season was the longest of our 8-year record. Before the dry season began, accumulation for the El Niño wet season 2009-10 was the lowest of our record (until this year), with maximum snowdepth reaching 1.79 m on 12 April. So, with lower than normal snowfall and a prolonged dry season - in which albedo steadily decreases - the snowline likely reached a considerably higher elevation than shown in the 2010 image, acquired two months before the dry season ended.

This year, maximum snowdepth was comparable to 2010 (1.78 m), yet reached a month earlier (18 March). A few snowfall events during April and early May have added mass, yet as of 15 May the surface is dropping below the mid-March height. This year and 2010 are the 2 lowest years of accumulation since our measurements began in 2004 (measured as snow depth, without consideration for density). For the first day of May both years, accumulation was >25 cm below the median depth (not shown in figure).

On Quelccaya this July we will measure density profiles and determine the more important measure of accumulation, which is water equivalent. If our team stays strong and our shovels don't all break, we will attempt to reach what remains of 2009-10 accumulation - assuming the 2010 snowline didn't rise above the summit!

2012-13 accumulation update

The 2012-13 wet season on Quelccaya began in earnest ~1 November, when the glacier surface reached its lowest height for the year. A snowy interval at the end of September may have marked the seasonal change in larger-scale circulation, yet this snow all ablated by the end of October and was not preserved.

As of 1 April, net accumulation for the season amounted to ~1.7 meters of snow. This is the least accumulation measured on this date for our 10-year period of record. Only slightly more snowfall had accumulated by this date during the 2009-10 season, one that ended by mid-April and was followed by the greatest ablation we have observed (>0.7 m lowering).

In another month or so the wet-dry season transition will be underway, and we will have a more comprehensive perspective on 2012-13 accumulation. The actual mass addition (water equivalence) will not be known until we are on-site for fieldwork; plans are being made to dig a massive snowpit, for sampling and observations back to 2009-2010 accumulation!

Radiation data!

Measurements of all four radiation terms have just been processed for June 2010 to July 2012 - the period over which a Kipp & Zonen CNR4 operated at the station. This is an exciting milestone, for working with such data from an extreme-environment AWS is not trivial; riming, snowfall, and intense solar radiation all influence measurements and necessitate adjustments. More importantly, radiation balance fluctuations considerably influence mass balance at the site, and processes of ice core development.

So for a quick overview, the lower plot below shows monthly mean values for 2010-11 (left bars, blue line) and for 2011-12 (right bars, dark blue line). Net solar is shown in orange, net longwave is red, and the lines are net all-wave radiation. Note a clear seasonality to both net shortwave and net longwave, and the relative accordance of monthly values for both years. At 14°S latitude, solar irradiance at the top of the atmosphere is most intense in February and least so in June, yet halfway through the atmosphere on the glacier, the seasonal pattern differs for both incoming and net solar. The seasonal cycle of net longwave radiation broadly mirrors that of net solar, with the greatest energy loss during months of high solar gain.

The upper plot is a timeseries of snow ablation and accumulation for the two years, June through May. Plotting the datum for each year relative to the annual minimum surface height at the station highlights differences in the timing of height changes.

The snow plot provides an valuable context to account for the observations above. The dry season on Quelccaya is typically May through August, when incoming solar radiation is relatively low, yet increasing dust concentration lowers albedo - and thus net solar receipt. Clear skies result in dramatically less longwave energy from the atmosphere than is lost from the snow surface. The transitional periods between seasons are very important to the energy balance, as shown by the contrast between a year when the dry season lingered (e.g., 2010 blue line) and the following year (dark blue line) in which a snowfall event buried the dry season surface by mid-September. With continuing clear sky and relatively darker snow in 2010, net solar irradiance averaged roughly 50 W/m^2 higher through September, easily offsetting the greater net longwave loss (due less cloud cover)! Without a substantial snowfall event until the end of November, and incoming solar radiation seasonally increasing rapidly each day, 2010 ablation (blue line) during these months was considerable relative to June-August, and the transient snowline likely reached a high elevation on the glacier. Unfortunately, suitable Landsat scenes for that year have not been identified after mid-September (Hanshaw and Bookhagen, The Cryosphere Discussions, 2013).

During both years shown, snow accumulation was greatest during February. Cloud cover and fresh snow likely account for low values of both net solar and net longwave radiation. Lastly, the snow plot illustrates that the 2011-12 wet season (dark blue line) ended earlier than the prior year (i.e., March), as also indicated by higher net solar and longwave radiation during March.

Also essential in understanding the Quelccaya energy balance are turbulent fluxes of sensible and latent heat. Along with estimating the radiation balance for the entire period of record at the site, efforts to determine these energy fluxes continue. The objective is quantifying the magnitude and timing of mass flux due to melting and meltwater percolation, which profoundly influences all aspects of the ice core record.

Air Temperature Measurements [updated]

Quelccaya's automated weather station (AWS) is providing a unique perspective on the tropical mid-troposphere, documenting modern climate at one of the world’s most important high-elevation paleoclimate sites. Air temperature data from the station are now available through the links below.

History
A brief synopsis of paleoclimate research on Quelccaya Ice Cap (with images) is available here. A paper presenting the 2003 ice core record – spanning over 1,600 years – is well underway.

In conjunction with Quelccaya paleoclimate research, meteorological instrumentation was operated at several locations on the glacier through the late 1970s and early 1980s. The objective was to begin characterizing the largely-unknown climate at high elevations in the Andes, an effort carried out collaboratively with Stefan Hastenrath. Despite working with equipment that is considered rather unreliable by today’s standards, several publications resulted.

During the 2003 ice-core drilling expedition, meteorological measurements resumed – with modern electronics, satellite telemetry, and a new tower design. Images of the new AWS can be seen at the link above, and here.

AWS data
Measuring atmospheric properties is not trivial, especially when the goal is to assess any change in central tendency, variability, or extremes over time (i.e., climate). A set of ten climate monitoring principles proposed by Tom Karl at NOAA provides a succinct starting point to learn more about issues involved.

At the summit of Quelccaya Ice Cap the AWS is seen only by high-flying birds for all but a few days each year. Consequently, all data require considerable processing and inspection to insure that measurements are valid and meaningful, and free of systematic errors. This process is underway for AWS measurements from a comprehensive suite of sensors (see images).

The first data being made available from Quelccaya are air temperature measurements from highly-accurate sensors developed for NOAA’s Climate Reference Network (CRN). These sensors are identical to those used for the CRN system, resulting from years of development by NOAA's National Climatic Data Center and their Atmospheric Turbulence and Diffusion Division. For detailed information on CRN, as well as data access, click here.

Quelccaya data
The following links provide access to provisional air temperature data. Please be sure to read the metadata document.
  metadata (PDF)
  hourly values
  monthly values

[UPDATE 3/25/2014:  A complete record of quality-controlled hourly air temperatures for July 2007-June 2009 are available here, as well as the accompanying metadata, and these values should be used rather than those above - which were provisional. 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.]


Contact for any questions or comments:  dhardy@geo.umass.edu