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.

View to the west

An automated camera on the AWS records both the glacier surface evolution and riming of the station. The clip below was assembled from images taken over a 5-month interval, at a time of day which best shows surface texture. Not all days were included here, as the surface isn't visible when rime obscures the camera housing window!

The date stamp on each image allows meteorological conditions to be assessed at the time. For example, drifting snow is evident on 24 October, when wind speed was ~9 m/s; or compare albedo on 25 or 27 October (~0.62) with that on 2 November (0.84). Although not immediately apparent in these images, the 2011 dry season on Quelccaya ended on 9 September, when the glacier surface was ~18 cm lower than that in the first image (10 July).

Accumulation update for 2012 - 2013

Accumulation on Quelccaya began in earnest during mid-November this year, which is relatively late. Two earlier snowfall events - in late September and early November - were followed by settling and ablation. Although these events contributed mass, they did not result in a surface height increase.

With a relatively prolonged 2012 dry season, and possibly melting of these two early snowfall events, the mid-November commencement of accumulation should be easily recognizable in the snowpack during 2013 fieldwork.

For the current accumulation season through yesterday, snow depth on the glacier is now at 1 meter. This is about the average for mid-January. With ENSO-neutral conditions in the tropical Pacific predicted to continue into the dry season at Quelccaya, another meter of accumulation is likely by early April.

10 years for the US Climate Reference Network

Congratulations to the USCRN program on the first decade of operations!

Some of the equipment on the UMass Quelccaya weather station is compatible with that of the U.S. Climate Reference Network (USCRN), which NOAA's National Climatic Data Center (NCDC) began 10 years ago. We chose to incorporate elements of their system at our site as a result of the extensive testing and characterization they carried out. A nice overview of all USCRN aspects and prospects is contained in the Early Online Release of a paper titled "U.S. Climate Reference Network after One Decade of Operations: Status and Assessment." The paper will appear in a future issue of the Bulletin of the American Meteorological Society, and is freely available now from this link.

To stay updated on further developments of the USCRN, follow NCDC on Twitter:  @NOAANCDC

Fieldwork photos

Photos from this year's fieldwork are in 3 different galleries:

1. At the summit our efforts were focused on the weather station (AWS), and in a snowpit as time permitted. Photos here. 
2. Working at an elevation of nearly 6,000 meters requires adapting to less oxygen (lower partial pressure), providing time to make other observations. Photos from travel to the ice cap and at the margin are here. For several locations - including outlet glacier Qori Kalis - photos from previous years have been mixed in to illustrate ice recession and thinning.
3. Among other observations possible while acclimatizing is documenting the elevation and habitats of various bird species living at this high elevation; the Quelccaya margin (~5,200 m or 17,000 ft) represents the upper end of most species' range. Photos of birds seen in 2012 are here (Additional Vilcanota birds can be seen here and here, or this link for more on Diuca speculifera.)

Please get in touch with any questions or comments!

Fieldwork weather

The figure above depicts summit weather at Quelccaya prior to and during our 2012 fieldwork. The short synopsis is that during our time at Moraine Camp and the AWS we experienced clear sky, low humidity, and low wind speeds. Just prior was an interval of high humidity, snowfall, moderately-high wind speeds, and lower temperatures.

Here are some details shown in the graph, and implications (click the graphic to see a larger version). Some measurement are presented only through the 11th due to sensor changes and service. We were at the summit from the 9th through the 15th, and near the ice cap 6-16 July:

1. Hourly incoming solar radiation is shown in orange. Clear sky continued from the 9th through until the 15th (not shown).
2. Blue squares are average daily relative humidity, which increased during our time in Cusco and then dropped abruptly on the day we first reached the summit.
3. Snow accumulation & ablation is depicted as the dashed blue line. This is actually a smoothed recording of changes in surface height, where decreasing distance represents snowfall and increasing distance is a combined record of melting, sublimation, wind scour and settling. The measurements are hourly, yet must be smoothed to remove a spurious diurnal cycle due to the impact of air path temperature on the speed of sound - since acoustic sensors are used. Anyway, processes were less continuous than the smoothed plot indicates, suggesting:  a) about 1.5 cm of snowfall during the afternoon of July 4th, b) another ~1.5 cm of snowfall late on the 5th, and c) ~1.5 cm of sublimation on the 9th. Note perfect conditions for sublimation on the 9th, including clear sky and high radiation, decreasing humidity, high wind speeds and lowest temperatures of the interval.
4. Average wind speed (red diamonds) parallels the humidity pattern, reaching a maximum on the day gear was carried to the summit and then dropping. For several 24-hour periods, it averaged < 3 m/s, and on our 'hottest' day of work at the station the average wind speed was <2 m/s - or <5 miles/hour. Very calm, especially at nearly 6,000 m elevation in the Andes.
5. Two different measurements of temperatures are represented on the graph, both as triangles and both as the maximum hourly values each day. The pink values are measurements in a naturally-ventilated, multiplate radiation shield whereas the cyan symbols depict measurements in a sophisticated, fan-aspirated shield compatible with the US CRN system (Climate Reference Network). Note that radiation shield differences can yield huge differences in measured temperature:  on 2 days in this interval the difference is >6°C. If data were available from the multiplate shield on the 13th (sensor was being replaced) a 10+ degree difference would not be surprising. Wind speed and solar radiation critically influence temperature measurement!

Photos of fieldwork activity will be posted shortly to illustrate the weather depicted above, so stay tuned! Measurements now continue autonomously at the station, transmitted hourly to us via telemetry.

Un gigapan muy grande

As previous posts have indicated, Quelccaya is a large, relatively-flat ice cap. From the summit area, ice flows down and out toward the margins with much of the flow taking place via outlet glaciers such as Qori Kalis. We shot several GigaPans at Qori Kalis this month, including the broad panorama below. Additional details about Qori Kalis and the composite panorama can be seen in a new tab by clicking on the image caption (or here for those w/o Flash). Details of the glacier are best seen in the second GigaPan below (or here). Several others will be posted shortly, illustrating details of the lake/moraines as well as areas nearby.