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Elevation gradients of meteorological variables in mountains are of interest to a number of scientific disciplines and often required as parameters in modeling frameworks. Measurements of such gradients on glaciers, however, are particularly scarce and strongly skewed towards the midlatitudes and valley glaciers. This article adds a tropical perspective and presents 4 years of overlapping measurements at 5603 and 5873 m on Kersten Glacier, Kilimanjaro (East Africa), between 2009 and 2013. Mean gradients in near-surface air temperature (T), water vapor pressure (VP), and snow accumulation (ACC) per 100 m elevation are −0.75 ∘C, −0.16 hPa, and -114±16 mm w.e. yr−1, respectively. An intriguing feature is a strong diurnal cycle of the T and VP gradients, which are (depending on season) 2–4 times larger between early and late morning than in the hours of weak gradients. The ACC decrease with elevation, furthermore, is mostly the result of a lower recorded frequency of ACC events at the upper measurement site and not due to contrasting amounts at the two altitudes during events. A novel facet of our study is the linking of measured on-glacier gradients to a high-resolution atmospheric modeling data set, which reveals the importance of the mesoscale atmospheric circulation. A thermally direct circulation is established over the mountain in response to diabatic surface heating or cooling with upslope flow during the day and downslope flow in the night. This persistent circulation communicates heat and moisture changes in the lowlands to the higher elevations during morning and early afternoon, which is evident in the advection patterns of potential temperature and VP, and shapes the time variability in gradients as recorded by our weather stations on the glacier. A few local processes seem to matter as well (glacier sublimation, turbulent heat fluxes), yet they show a secondary influence only during limited time windows. Atmospheric model data also demonstrate that declining moist entropy and water vapor fluxes in the summit zone favor formation of the negative ACC gradient. The results extend the empirical basis of elevation gradients in high mountains, in particular over glacier surfaces, by the unusual case of a slope glacier on an equatorial, free-standing massif. Our measurement–model link, moreover, demonstrates an approach for future studies to put observations of elevation gradients more systematically in a multiscale process context.

We analyze the future state of Quelccaya Ice Cap (QIC), the world’s largest tropical ice cap with a summit elevation of 5680 m a.s.l., which, in terms of its elevation range (~5300–5680 m a.s.l.), is representative of many low-elevation glacierized sites in the tropical Andes. CMIP5 model projections of air temperature (Ta) at QIC indicate a warming of about 2.4 °C and 5.4 °C (respectively) for RCP4.5 and RCP8.5 scenarios by the end of the 21st century, resulting in a pronounced increase in freezing level height (FLH). The impact of this warming on the QIC was quantified using equilibrium-line altitude (ELA) projections. The change in the ELA was quantified based on an empirical ELA–FLH relationship, and calibrated with observations of the highest annual snowline altitude (SLA) derived from LANDSAT data. Results show that from the mid-2050s onwards, the ELA will be located above the QIC summit in the RCP8.5 scenario. At that time, surface mass balance at QIC and most tropical glaciers at similar elevations will become increasingly negative, leading to their eventual complete disappearance. Our analysis further corroborates that elevation-dependent warming (EDW) contributes significantly to the enhanced warming over the QIC, and that EDW at Quelccaya depends on the rate of anthropogenic forcing.

Tropical ice core archives are among the best-dated and highest-resolution from the tropics, but a thorough understanding of processes that shape their isotope signature as well as the simulation of observed variability remain incomplete. To address this, we develop a tropical Andean ice core isotope forward model from in situ hydrologic observations and satellite water vapor isotope measurements. A control simulation of snow δ18O captures the mean and seasonal trend but underestimates the observed intraseasonal variability. The simulation of observed variability is improved by including amount effects associated with South American cold air incursions, linking synoptic-scale disturbances and monsoon dynamics to tropical ice core δ18O. The forward model was calibrated with and run under present-day conditions, but can also be driven with past climate forcings to reconstruct paleo-monsoon variability. The model is transferable and may be used to render a (paleo)-climatic context at other ice core locations.

Spatially high resolution climate information is required for a variety of applications in but not limited to functional biodiversity research. In order to scale the generally plot-based research findings to a landscape level, spatial interpolation methods of meteorological variables are required. Based on a network of temperature observation plots across the southern slopes of Mt. Kilimanjaro, the skill of 14 machine learning algorithms in predicting spatial temperature patterns is tested and evaluated against the heavily utilized kriging approach. Based on a 10-fold cross-validation testing design, regression trees generally perform better than linear and non-linear regression models. The best individual performance has been observed by the stochastic gradient boosting model followed by Cubist, random forest and model averaged neural networks which except for the latter are all regression tree-based algorithms. While these machine learning algorithms perform better than kriging in a quantitative evaluation, the overall visual interpretation of the resulting air temperature maps is ambiguous. Here, a combined Cubist and residual kriging approach can be considered the best solution.

Direct measurements of the decadal response of Tropical glaciers to environmental changes are difficult to acquire within their accumulation zones. In 2013, we used dual-frequency kinematic GPS to re-measure the surface elevations at 46 sites, from the margin to across the summit of the Quelccaya Ice Cap, first measured in 1983 using terrestrial surveying methods. In 2015, six additional sites on the western margin, first observed in 1978, were remeasured. Over the past 30 years, the ice cap summit has thinned by 4.41 ± 0.23 m (2σ), with a maximum ice loss at one site near the margin of 63.4 ± 0.34 m (2σ) over 37 years. Using geophysical methods that located the sub-glacial bedrock, we estimate the unit-volume of ice in 1983 along a profile from the 1983 margin to the summit and then the change in volume from 1983 to 2013 by differencing the surface elevations. Over the past 30 years, 21.2 ± 0.3 % (2σ) of the ice unit-volume has been lost suggesting an average annual mass balance rate of −0.5 ± 0.1 m w.e. a−1 (2σ). Increasing air temperature at high elevations of the Andes is likely a major driver of the observed changes. Specifically, within the ablation zone, thinning is likely caused by a 1–2 m w.e. a−1 increase in melting and sublimation above steady-state.Within the accumulation zone, analysis of annual, dry-season summit pits suggests that surface lowering may be caused by both a slight decrease in net snow accumulation and an increase in firnification rate, though this interpretation yet lacks statistical significance. The role of ice flux changes since 1983/4 remains unconstrained, awaiting updated measurements of ice surface velocities across the ice cap.

Quelccaya Ice Cap in the Andes of Peru contains an annually resolved δ18O record covering the past 1800 years; yet atmospheric dynamics associated with snow deposition and δ18O variability at this site are poorly understood. Here we make use of 10 years of snow pit and short core δ18O data and hourly snow-height measurements obtained by an automated weather station deployed at the ice cap's summit to analyze linkages between snowfall, δ18O, and the South American summer monsoon (SASM). Snow accumulation peaks in December and is negative May–September. Snow δ18O values decrease gradually through austral summer from about −17 to −24‰. Surface snow δ18O is altered after deposition during austral winter from about −24 to −15‰. More than 70% of the total snow accumulation is tied to convection along the leading edge of cold air incursions of midlatitude air advected equatorward from southern South America. Snowfall amplitude at Quelccaya Ice Cap varies systematically with regional precipitation, atmospheric dynamics, midtroposphere humidity, and water vapor δD. Strongest snowfall gains correspond with positive precipitation anomalies over the western Amazon Basin, increased humidity, and lowered water vapor δD values, consistent with the “amount effect.” We discuss ventilation of the monsoon, modulated by midlatitude cold air advection, as potentially diagnostic of the relationship between SASM dynamics and Quelccaya snowfall. Results will serve as a basis for development of a comprehensive isotopic forward model to reconstruct past monsoon dynamics using the ice core δ18O record.

Although its Holocene glacier history is still subject to debate, the ongoing iconic decline of Kilimanjaro's largest remaining ice body, the Northern Ice Field (NIF), has been documented extensively based on surface and photogrammetric measurements. The study presented here adds, for the first time, ground-penetrating radar (GPR) data at center frequencies of 100 and 200 MHz to investigate bedrock topography, ice thickness and internal stratigraphy at NIF. The direct comparison of the GPR signal to the visible glacier stratigraphy at NIF's vertical walls is used to validate ice thickness and reveals that the major internal reflections seen by GPR can be associated with dust layers. Englacial reflections can be traced consistently within our 200 MHz profiles, indicating an undisturbed internal stratigraphy within NIF's central flat area. We show that it is possible to follow isochrone layers between two former NIF ice core drilling sites and a sampling site on NIF's vertical wall. As a result, these isochrone layers provide constraints for future attempts at linking age-depth information obtained from multiple locations at NIF. The GPR profiles reveal an ice thickness ranging between (6.1 ± 0.5) and (53.5 ± 1.0) m. Combining these data with a very high resolution digital elevation model we spatially extrapolate ice thickness and give an estimate of the total ice volume remaining at NIF's southern portion as (12.0 ± 0.3) 106 m3.

We take advantage of the spatial coverage provided by the Tropospheric Emission Spectrometer on-board the Aura satellite to evaluate processes that control seasonal variations in atmospheric water vapor HDO/H2O values (δDvapor) over the tropical Andes. δDvapor is lower in austral summer (December, January, and February, DJF) than austral winter (June, July, and August, JJA), which is broadly consistent with precipitation studies and with δ18Osnow preserved in tropical Andean glaciers. In DJF, 64% of δDvapor measurements over the tropical Andes are lower than predicted by Rayleigh distillation while 40% of JJA δDvapor measurements are lower than predicted by Rayleigh distillation. Air that has lower δDvapor than predicted by Rayleigh distillation at a given water vapor concentration (q) encounters low minimum outgoing longwave radiation (

Two pairs of small stagnant ice bodies on the Hazen Plateau of northeastern Ellesmere Island, the St. Patrick Bay ice caps and the Murray and Simmons ice caps, are rapidly shrinking, and the remnants of the St. Patrick Bay ice caps are likely to disappear entirely within the next 5 years. Vertical aerial photographs of these Little Ice Age relics taken during August of 1959 show that the larger of the St. Patrick Bay ice caps had an area of 7.48 km2 and the smaller one 2.93 km2; the Murray and Simmons ice caps covered 4.37 and 7.45 km2 respectively. Outlines determined from ASTER satellite data for July 2016 show that, compared to 1959, the larger and the smaller of the St. Patrick Bay ice caps had both been reduced to only 5 % of their former area, with the Murray and Simmons ice caps faring better at 39 and 25 %, likely reflecting their higher elevation. Consistent with findings from other glaciological studies in the Queen Elizabeth Islands, ASTER imagery in conjunction with past GPS surveys documents a strikingly rapid wastage of the St. Patrick Bay ice caps over the last 15 years. These two ice caps shrank noticeably even between 2014 and 2015, apparently in direct response to the especially warm summer of 2015 over northeastern Ellesmere Island. The well-documented recession patterns of the Hazen Plateau ice caps over the last 55+ years offer an opportunity to examine the processes of plant recolonization of polar landscapes.

article i nfo We compare surface climate (temperature and moisture) measured on an hourly basis at ten elevations on

Glaciers on Kilimanjaro’s highest peak, Kibo, are currently regarded as a persistent feature of the Holocene. Here we synthesize all available measurements, observations, and our understanding of current processes on Kibo — gained from intensive research over the past decade — to formulate an alternative hypothesis about the age of these ice fields. This suggests a shorter, discontinuous history of the tabular-shaped glaciers on Kibo’s plateau, where typical ‘life cycles’ of the ice may last only a few hundred years. If life cycles overlap, they are likely the cause of the observed steps in the plateau glaciers. Thus, it is likely that ice has come and gone repeatedly on Kibo’s summit plateau, throughout the Holocene. Such a cyclicity is supported by lake-derived proxy records.

Land-based ice cliffs are intriguing features at the margins of glaciers around the world, but little is known about mechanisms of their formation and maintenance. A review on those ice cliffs, which are mostly associated with dry calving events, is presented. The focus is on the persistent, rarely-calving ice cliffs on the plateau glaciers of Kibo, the main peak of the Kilimanjaro massif (3°S, 37°E), Tanzania. Areal glacier shrinkage on Africa’s highest peak is closely linked to the recession of these ice cliffs and in order to extract climate change details from the plateau glaciers on Kilimanjaro, the sensitivity of the cliffs to climate fluctuations must be understood. Modelling solar irradiance, in conjunction with on-site measurements, revealed that direct insolation is the reason for (1) the predominant zonal alignment of the ice cliffs and (2) their bimodal annual recession. The former peculiarity occurs because near the equator steep northand south-facing slopes receive only little solar energy, which prevents strong ablation. The bimodal recession pattern is caused by the particular annual path of the sun in the tropics, which either induces strong direct insolation on the Kilimanjaro ice cliffs from sunrise to sunset (“sunlit period”), or comparatively low (or no) direct insolation all day (“shaded period”). A 26 m high, 69° steep, and approximately south-facing sample cliff has been surveyed by terrestrial photogrammetry. The daily direct maximum insolation threshold between sunlit and shaded periods at the sample cliff is about 680 Wm-2. During the shaded period from March 4th to October 11th, where mean recession is only 1.4 cm/month, daily maximum insolation at the inclined sample cliff surface is below this threshold. During the sunlit period (mean recession rate ~13 cm/month) daily insolation maxima exceed this threshold.

The dramatic loss of Kilimanjaro's ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased approximately 1% per year from 1912 to 1953 and approximately 2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was approximately 1.9 and approximately 5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of approximately 3.6% and approximately 24%, respectively. Furtwängler Glacier thinned approximately 50% at the drill site between 2000 and 2009. Ice volume changes (2000-2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaro's ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought approximately 4,200 years ago that lasted approximately 300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro's ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.

Slope glaciers on Kilimanjaro (ca. 5000–6000 m MSL) reached their most recent maximum extent in the late nineteenth century (L19) and have receded since then. This study quantifies the climate signal behind the recession of Kersten Glacier, which generates information on climate change in the tropical midtroposphere between L19 and present. Multiyear meteorological measurements at 5873 m MSL serve to force and verify a spatially distributed model of the glacier’s mass balance (the most direct link between glacier behavior and atmospheric forcing). At present the glacier is losing mass (522 ± 105 kg m−2 yr−1), terminates at 5100 m, and the interannual variability of mass and energy budgets largely reflects variability in atmospheric moisture. Backward modeling of the L19 steady-state glacier extent (down to 4500 m) reveals higher precipitation (+160 to +240 mm yr−1), higher air humidity, and increased fractional cloud cover in L19 but no significant changes in local air temperature, air pressure, and wind speed. The atmosphere in the simulated L19 climate transfers more energy to the glacier surface through atmospheric longwave radiation and turbulent heat—but this is almost entirely balanced by the decrease in absorbed solar radiation (due to both increased cloudiness and higher surface albedo). Thus, the energy-driven mass loss per unit area (sublimation plus meltwater runoff) was not appreciably different from today. Higher L19 precipitation rates therefore dominated the mass budget and produced a larger glacier extent in the past.

We found evidence of birds nesting directly on glacier ice of the Quelccaya Ice Cap in the Cordillera Vilcanota, Peru at elevations up to 5,300 m. Observations during June and July over several years consisted of numerous nests not in situ having obviously fallen from the steep and dynamic, retreating glacier margin. A typical nest was a bulky structure of grass and twigs with a dry mass of 160 g. The inner cup was nicely formed and lined with fine grass, measuring 6–7 cm in diameter and 4–5 cm deep. Feathers and entire wings of White-winged Diuca Finch (Diuca speculifera) were observed in association with the nests; this was the passerine species most commonly seen in the area. The evidence indicates the glacier nests were built and used by White-winged Diuca Finch, probably during the Austral autumn when on-site automated measurements indicate the wet season ends and air temperatures have not yet decreased. This is the first well-documented case of high-elevation avian nesting on glacier ice.

Hourly temperature and humidity observations were obtained over 16 months from loggers ranging in elevation from 1890 to 5800 m a.s.l. up the southwestern slope of Kilimanjaro, Tanzania. The vertical gradient in mean air temperature is non-linear, with the treeline weakening the gradient and the snow-ice line enhancing it. On average, moisture availability (both relative humidity and absolute vapor pressure) decreases with elevation, but the seasonal and diurnal variability in relative humidity (RH) is enhanced toward the mountain summit. The strong diurnal cycle in humidity is shown to be an outcome of strong upslope moisture transport during the day, counterbalanced by downslope transport and drying at night. Cooling on the lower slopes during the months of June and July weakens the lapse rates and consequently convective activity. This is borne out by the reduction in cloud amounts (using a surrogate threshold of RH > 95%), toward the summit during these months. The lower slopes of Kilimanjaro...

Meteorological and glaciological measurements obtained at 5873 m a.s.l. on Kersten Glacier, a slope glacier on the southern flanks of Kilimanjaro, are used to run a physically-based mass balance model for the period February 2005 to January 2006. This shows that net shortwave radiation is the most variable energy flux at the glacier-atmosphere interface, governed by surface albedo. The majority of the mass loss (∼65%) is due to sublimation (direct conversion of snow/ice to water vapour), with melting of secondary importance. Sensitivity experiments reveal that glacier mass balance is 2–4 times more sensitive to a 20% precipitation change than to a 1 °C air temperature change. These figures also hold when the model is run with input data representative of a longer term (1979–2004) mean period. Results suggest that a regional-scale moisture projection for the 21st century is crucial to a physically-based prediction of glacier retention on Africa's highest mountain. Copyright © 2007 Royal Meteorological Society

Atmospheric circulation anomalies, related to snowfall events on the Tanzanian volcano Kilimanjaro, were analyzed based on hourly snowfall data from an automated weather station (AWS), global precipitation and reanalysis products. Analysis of 5 years of data (2000–2005) shows that snowfall on Kilimanjaro is linked to large-scale circulation anomalies, which can be identified in global reanalysis products. During the long rains season (March–May) snowfall on Kilimanjaro is associated with a west to east propagating wave of convective activity, which over East Africa merges with a precipitation-band maintained by steady easterly moisture influx due to cyclonic activity over northern Madagascar. Snowfall events tend to be associated with low wind speed, favorable for the development of surface radiative heating, thereby destabilizing the atmospheric column and initiating upward motion and deep convection. High near-surface specific humidity provides the necessary water vapor so that convection becomes moist. The short rains season (October–December) is dominated by east to west moisture transport. This easterly flow extends vertically through much of the troposphere and horizontally from the western Indian Ocean westward across the African continent. An active center of vertical motion and deep convection located over the western Indian Ocean near the East African coastline is responsible for easterly moisture transport and spill-over of precipitation into the East African domain. During positive phases of the Indian Ocean Zonal Mode (IOZM) strong trade winds prevail across the Indian Ocean, which, in combination with enhanced westerlies over the continental interior, tend to enhance low-level wind and moisture convergence near Kilimanjaro. During the negative IOZM phase on the other hand, the trade winds across the Indian Ocean and the westerly flow from the Atlantic Ocean are weaker, moisture convergence is reduced and conditions to initiate deep convection over Kilimanjaro are generally less favorable.

Eddy covariance data collected over a horizontal surface on the largest ice body on Kilimanjaro, Tanzania, over 26–29 July 2005 were used to assess the uncertainty of calculating sublimation with a surface energy balance (SEB) model. Data required for input to the SEB model were obtained from an existing automatic weather station. Surface temperatures that were solved iteratively by the SEB model were used to compute emitted longwave radiation, turbulent heat fluxes using the aerodynamic bulk method and the subsurface heat flux. Roughness lengths for momentum and temperature, which were found to be the most important input parameters controlling the magnitude of modelled (bulk method) turbulent heat fluxes, were obtained using eddy covariance data. The roughness length for momentum was estimated to be 1.7×10–3 m, while the length for temperature was one order of magnitude smaller. Modelled sensible and latent heat fluxes (bulk method) compared well to eddy covariance data, with root-mean-square differences between 3.1 and 4.8 Wm–2 for both turbulent heat fluxes. Modelled sublimation accounted for about 90% of observed ablation, confirming that mass loss by melting is much less important than sublimation on the horizontal surfaces of the remaining plateau glaciers on Kilimanjaro.

Two large suspended sediment concentration (SSC) pulses were recorded in 1998 in a small snowmelt-fed stream on Ellesmere Island in the Canadian High Arctic. The largest pulse occurred from 7 to 8 July, when 32% of the monitored seasonal sediment transport occurred in only four hours. SSC reached 83,760 mg L−1, exceeding all previously recorded values from high arctic glacially-fed and snowmelt-fed rivers by more than one order of magnitude. The event occurred after the majority of snow in the watershed had melted, and was preceded by a long period of relatively high air temperature, and a small rainfall event on 7 July. We consider the most likely cause of the event to be a rapid mass movement.

In recent years, Kilimanjaro and its vanishing glaciers have become an ‘icon’ of global warming, attracting broad interest. In this paper, a synopsis of (a) field observations made by the authors and (b) climatic data as reported in the literature (proxy and long-term instrumental data) is presented to develop a new concept for investigating the retreat of Kilimanjaro's glaciers, based on the physical understanding of glacier–climate interactions. The concept considers the peculiarities of the mountain and implies that climatological processes other than air temperature control the ice recession in a direct manner. A drastic drop in atmospheric moisture at the end of the 19th century and the ensuing drier climatic conditions are likely forcing glacier retreat on Kilimanjaro. Future investigations using the concept as a governing hypothesis will require research at different climatological scales. Copyright © 2004 Royal Meteorological Society

Small, stagnating ice caps at high latitudes are particularly sensitive to climatic fluctuations, especially with regard to changes in ablation season temperature. We conducted mass balance measurements and GPS area surveys on four small High Arctic plateau ice caps from 1999-2002. We compared these measurements with topographic maps and aerial photography from 1959, and with previously published data. Net mass balance (b n ) of Murray Ice Cap was -0.49 (1999), -0.29(2000), -0.47 (2001), and -0.29 (2002), all in meters of water equivalent (m w.eq.). The mass balance of nearby Simmons Ice Cap was also negative in 2000 (b n = -0.40 m w.eq.) and in 2001 (b n = -0.52 m w.eq.). All four ice caps experienced substantial marginal recession and area reductions of between 30 and 47% since 1959. Overall, these ice caps lost considerable mass since at least 1959, except for a period between the mid-1960s and mid-1970s characterized regionally by reduced summer melt, positive mass balance, and ice cap advance. The regional equilibrium line altitude (ELA) is located, on average, above the summits of the ice caps, indicating that they are remnants of past climatic conditions and out of equilibrium with present climate. The ice caps reached a Holocene maximum and were several times larger during the Little Ice Age (LIA) and their current recession reflects an adjustment to post-LIA climatic conditions. At current downwasting rates the ice masses on the Hazen Plateau will completely disappear by, or soon after, the mid-21st century.

Mission Assurance, Threat Alert Disaster Resiliency and Response (MATADRR) is USNORTHCOM's joint initiative to enhance automated information sharing and mission assurance by establishing information sharing interfaces across currently stove piped unclassified emergency management/force protection applications. Its goal is to quickly disseminate time-critical incidents, imminent threats, and/or hazard information within the USNORTHCOM Domestic Area of Responsibility to streamline information sharing through automation. This document describes the MATADRR Keystone products and related non-materiel solutions. It identifies the organizations (with key points of contact [POCs]) using the Keystone solution, how each customized the solution, and how they agreed to transition it. Most importantly, this document provides information for obtaining Keystone products and support. Lastly, the document contains artifact information for use in Defense Technical Information Center (DTIC) for future programs and projects.

Terrestrial laser-scanning surveys of the south-facing cliff of the northern Ice Field on the summit crater of Kilimanjaro were taken on three occasions, in September 2004, January 2006, and August 2008. By comparing the three scans, the rates of lateral cliff retreat and surface lowering can be assessed. During 2004–2006, the mean lateral retreat was 1.39 m yr–1, falling to 0.89 m yr–1 during 2006–2008. These rates are broadly comparable with previous work using ablation stakes. Surface lowering is much less rapid, at 0.65 and 0.25 m yr–1, respectively. Analysis of seasonal forcings (radiation on a south-facing cliff, radiation on a flat surface, surface vapor pressure, and relative humidity) shows that most of the lateral retreat occurs during the austral summer, when direct radiative input is considerably higher on the south-facing ice cliff. On the ice surface, however, high-sun periods around the equinoxes dominate the surface lowering. Lowering is more during the wet than the dry seasons, which suggests that the current moisture availability on Kilimanjaro is not frequent enough to prevent lowering year round.

Ice fields on Kilimanjaro (5895 m a.s.l., Tanzania) are retreating and 85% of the ice cover has been lost since 1912. The degree to which this recession is exceptional during the Holocene is uncertain, as age control of the entire ice stratigraphy exists only for the very shallow and very bottom ice of the Northern Ice Field. This empirical evidence suggests that the Kilimanjaro ice cover may be a persistent Holocene feature, while a model based on maximum possible extent and a constant shrinkage rate of the summit glaciers suggests a cyclic decay time on the order of one to two centuries. Today the mass balance of these ice fields is negative and no persistent ice accumulation zones are observed over multiannual scales. The expanding deglaciated area within the Kilimanjaro caldera should act as an increasingly larger and productive source of volcanic-origin aeolian dust that is quickly deposited onto the surface of the adjacent ice fields, particularly in the seasonal absence of caldera snow cover. Variations in the local dust influx may directly influence albedo and the energy balance of these ice fields. Investigating the characteristics of insoluble material entrapped in the ice remnants of Kilimanjaro can thus provide insights into the extent of ice and/or continuity of the summit snow cover through time. Here we report the trace element composition linked to the insoluble particles entrapped in Holocene Kilimanjaro ice in the context of the current understanding of the past ice accumulation processes (including solid precipitations and ablation) contributing to build the horizontal caldera ice fields. For this purpose we analysed an ice core drilled to bedrock from the Northern Ice Field thought to span the late Holocene (2200 BC–1950 AD). The ultra low trace element concentrations recorded in this Kilimanjaro core are consistent with a generally low volcanic dust source availability (i.e. limited exposure of the deglaciated area in the caldera) and fairly continuous ice accumulation during the late Holocene. In contrast, the maximum concentrations for most of the trace elements recorded in the surface ice section suggest that the current lack of ice accumulation on the Kilimanjaro ice fields is unusual over the last ∼4 ka.

The importance of near-surface faceted crystals in forming weak layers associated with snow avalanches has recently received greater attention. However, there is still much to be learned concerning the formation and growth of these crystal types, their geographical extent, and related avalanche activity. Here we report on two avalanches that occurred during late September 1999 at high-elevations in the Bolivian Andes. Climbers released one slide at about 5200 m in the Cordillera Apolobamba (on El Presidente), which claimed two lives. Four days later and 200 km to the southeast, snow scientists servicing a high-elevation meteorological site triggered another at 6300 m near the summit of Illimani (Cordillera Real). Both slab avalanches fractured through 25–50 cm of relatively new snow, with deeper pockets of wind redistributed snow. Snowpit analyses on Illimani showed the avalanche ran on a thick layer of near-surface faceted crystals overlying the austral winter dry-season snow surface. Average crystal size was 5–7 mm, and individual crystals exceeded 10 mm in diameter. We evaluate local and regional meteorological information in an effort to understand what caused the growth of these large crystals and the resultant snowpack instability. Dust and chemistry profiles indicate that the crystal growth occurred through the austral winter, prior to a snowfall event in the days prior to the avalanche. Temperature profiles measured just above and just below the snow surface indicate that bi-directional, large gradients of temperature and vapor pressure exist through the dry winter season. Insights are offered regarding the avalanche hazard due to near-surface faceted crystal growth in high-elevation areas of the Tropics, where avalanches are not generally recognized as a significant hazard during the climbing season.

Hydrological and meteorological observations at Lake Tuborg, Ellesmere Island, Nunavut, Canada in 1995 are used to investigate contemporary water and sediment transport processes. Here we describe a new environmental data set for the High Arctic, where such data are scarce. The studied watershed (∼460 km2) ranges in elevation between 63 and ∼1900 m asl and is 88% covered by a lobe of the Agassiz Ice Cap. Streamflow and sediment transport were strongly associated with snowmelt runoff, whereas the direct influence of summer precipitation events was negligible. Snowmelt was primarily controlled by synoptic‐scale climatic processes. Two high‐magnitude pulses of meltwater and slush contributed a significant portion of the measured suspended sediment load to Lake Tuborg. Such events may be associated each year with snowmelt along the Agassiz Ice Cap margin. Additional years of data collection are needed to define the annual and inter‐annual variability of the sediment delivery system, particularly with...

The unique clinical and pathological findings in nine Asian (Elephas maximus) and two African (Loxodonta africana) elephants from North American Zoos with a highly fatal disease caused by novel endotheliotropic herpesviruses are described. Identification of the viruses by molecular techniques and some epidemiological aspects of the disease were previously reported. Consensus primer polymerase chain reaction (PCR) combined with sequencing yielded molecular evidence that confirmed the presence of two novel but related herpesviruses associated with the disease, one in Asian elephants and the second in African elephants. Disease onset was acute, with lethargy, edema of the head and thoracic limbs, oral ulceration and cyanosis of the tongue followed by death of most animals in 1 to 7 days. Pertinent laboratory findings in two of three clinically evaluated animals included lymphocytopenia and thrombocytopenia. Two affected young Asian elephants recovered after a 3 to 4 wk course of therapy with the anti-herpesvirus drug famciclovir. Necropsy findings in the fatal cases included pericardial effusion and extensive petechial hemorrhages in the heart and throughout the peritoneal cavity, hepatomegaly, cyanosis of the tongue, intestinal hemorrhage, and ulceration. Histologically, there were extensive microhemorrhages and edema throughout the myocardium and mild, subacute myocarditis. Similar hemorrhagic lesions with inflammation were evident in the tongue, liver, and large intestine. Lesions in these target organs were accompanied by amphophilic to basophilic intranuclear viral inclusion bodies in capillary endothelial cells. Transmission electron microscopy of the endothelial inclusion bodies revealed 80 to 92 nm diameter viral capsids consistent with herpesvirus morphology. The short course of the herpesvirus infections, with sudden deaths in all but the two surviving elephants, was ascribed to acute cardiac failure attributed to herpesvirus-induced capillary injury with extensive myocardial hemorrhage and edema.

An automated weather station was installed in October 1996 at the summit of Nevado Sajama, located in the western Andean Cordillera of Bolivia (6542 m, 18°06´S, 68°53´W). Meteorological conditions on the mountain are being observed to improve the calibration of geochemical variations within tropical ice cores. This article documents the design and operation of the station and presents a discussion of measurements made through the first annual cycle. Variables analyzed include pressure, incoming solar radiation, air temperature, humidity, wind, and snow accumulation. Large diurnal fluctuations were recorded in most variables, which is not unexpected given the location at 18°S; the data also reveal substantial day-to-day variability and rapid seasonal changes in weather and circulation. As a result, snowfall events and periods of evaporation are more episodic in nature than previously believed. Measurement of atmospheric conditions during and between snowfall events will therefore greatly facilitat...

The analysis of atmospheric circulation anomalies related to snowfall events on Sajama volcano (Bolivian Andes) provides important information for the calibration of an ice core, recently recovered from the summit. Seventeen precipitation episodes were recorded on Sajama volcano during the 1996/1997 summer season (November 1996 to March 1997) by snow depth sensors and additional measurements of an automatic weather station located on the summit. The analysis of atmospheric circulation patterns during these events is based on zonal and meridional wind, air temperature, relative humidity, geopotential height and horizontal divergence at three pressure levels (400, 500, and 700 hPa levels), atmospheric thickness (700 hPa-400 hPa), and precipitable water (vertically integrated), all extracted from the National Centers for Environmental Prediction (NCEP) data set. Highly convective situations prevailed through most of December and January, with strong vertical motion over the Bolivian Altiplano. In February and March, increased moisture advection from the east occurred in midtropospheric levels. These results are confirmed by isobaric 5-day back trajectories and transit time analysis at the 400 hPa level. The extremely southern position of the upper air high-pressure system (“Bolivian High”) in February and March is the main reason for the unusually high precipitation amounts on the Altiplano in 1996/1997. Highly variable patterns of atmospheric circulation can lead to snowfall on Sajama during the summer months.

Our paper (1) does not seek to review all potential controls on glacier mass balance (MB) but to (i) present ice volume-change calculations, revealing that glacier thinning now accounts for ∼50% of the ice-volume loss for the summit ice fields, (ii) update changes in the areal extent of the ice fields based on newer (2007) aerial photographs, and (iii) highlight that ice loss on Kilimanjaro is not exceptional. We disagree with Molg et al. (2) that we inappropriately propose that Kilimanjaro’s “shrinking ice fields are not unique” (1). The reduction in areal extent and ice volume (shrinking) of Kilimanjaro’ si cefields is not unique; it isconsistentwiththewell-documentedwidespread glacier retreat in lower latitudes. Molg et al. (2) obfuscate the issue of Kilimanjaro’s glacier recession by not differentiating between processes responsible for decreasing ice area (i.e., vertical wall retreat) and more typical MB processes acting on horizontal surfaces, where the balance is currently negative. In fact, since 2000, we have documented area-weighted plateau thinning of ∼4 m, a tremendous increase over the rate of 1 m per

[1] The height of the freezing level in the tropical atmosphere (the free air 0°C isotherm) has increased across most of the region, particularly in the outer Tropics. In the tropical Andes, south of the Equator, high elevation surface temperatures and upper air data show a similar trend in temperature, of ∼0.1°C/decade over the last 50 years. Meteorological observations at 5680 m on the summit of the Quelccaya Ice Cap, the largest ice mass in the Tropics, indicate that daily maximum temperatures often exceed 0°C from October–May, and rise well above freezing for much of the year around the ice cap margin at 5200 m. This is consistent with observations of a rise in the percolation facies (an indicator of surface melting) in recent decades, and other observations of marginal recession, showing that the ice cap is rapidly losing mass. Similar conditions are likely to be affecting other high elevation ice caps and glaciers in Ecuador, Peru and Bolivia, with important implications for water supplies in the region. Over the Tropics as a whole, freezing level height (FLH) is closely related to mean SSTs, with inter-annual variations in FLH controlled by the phase of ENSO variability. More extensive monitoring of climatic conditions at high elevations in the mountains of the Tropics is urgently needed.

[1] Recent and long term variations in ice extent on Kilimanjaro are investigated in the context of 20th century climate change in East Africa. Quickbird satellite data show that the areal extent of glaciers on Kilimanjaro is 2.51 km2 in February 2003. To assess glacier retreat on Kilimanjaro two glacier systems are identified: (1) plateau (≥5700 m) and (2) slope (

[1] The Ward Hunt Ice Rise and Ward Hunt Ice Shelf, located on Ellesmere Island, Canada, are two of the northernmost land ice masses on the North American continent. Surface mass balance measurements (excluding calving and subice processes) began in 1959 on the ice rise and in 1966 on the ice shelf but were frequently interrupted, most recently between 1986 and 2002. The surface balance of the ice rise and ice shelf follows the temporal pattern seen on other measured High Arctic glaciers. The overall surface mass losses over the last 45 years have been comparatively low (1.68 m water equivalent (w eq) for the ice rise and 3.1 m w eq for the ice shelf), which reflects their proximity to the Arctic Ocean. Nevertheless, the ice shelf appears to have weakened sufficiently in recent years to raise concerns about its possible disintegration in the near future. The 2002/2003 balance year was the most negative year on record (−0.33 m w eq for the ice rise and −0.54 m w eq for the ice shelf). Dynamical stresses related to wind, wave, and tidal action may further accelerate this process, as open water conditions on the Arctic Ocean become more prevalent. The Ward Hunt Ice Rise has so far remained in a reasonably healthy state in terms of its overall surface mass balance, although its long-term survival is also threatened by current and predicted future climatic conditions.

This paper proposes the standardization of a layered simulation architecture that addresses the critical modeling needs of the DoD simulation community. The Standard Simulation Architecture works with HLA to provide the additional infrastructure necessary for developing highly inter-acting, decoupled software models, while simultaneously supporting technology infusion from R&D organizations. A layered architecture is proposed to modularize critical capabilities including high-speed communications between nodes in a multiprocessing federate, general-purpose software utilities, modeling semantics, time management, interest management, and automated interoperability with HLA. The interface layers must be standardized to promote (1) model development, (2) portability and interoperability with other models, (3) scalable high performance, and (4) technology infusion from the research community. Through the standardization process, COTS, GOTS, and Open Source business models are supported. The Standard Simulation Architecture extends interoperability and reuse principles to (1) the entities residing within a multiprocessing federate and to (2) the components hierarchically residing within an entity or within components. This standardized hierarchical modeling paradigm promotes development of reusable entity and component repositories that can be reused to support different modeling applications. Instead of providing only course-grained interoperability through HLA, the Standard Simulation Architecture also supports medium and fine-grained interoperability between entities and their components.

[1] The surface energy balance of a glacier describes the physical connection between ice/snow ablation and climatic forcing. To expand knowledge on the response of Kilimanjaro's glaciers to climate variations, this study estimates the energy balance on a horizontal glacier surface at the summit for the periods March to September 2000 and March 2001 to February 2002. An automatic weather station (AWS) operating at 5794 m above sea level provides the data input, and ablation at the AWS site differed considerably between the two periods. The energy balance model employed incorporates radiative fluxes, turbulent heat fluxes, and the energy flux in the subsurface. On a monthly basis, results show that radiative energy dominates energy exchanges at the glacier-atmosphere interface, governed by the variation in net shortwave radiation. The turbulent latent heat flux, which is always negative (i.e., continuous mass loss due to sublimation), is the second important energy flux. In contrast, turbulent exchange of sensible heat remains of minor importance. The marked difference in ablation between the two periods can largely be explained by a difference in surface albedo. Albedo depends on precipitation amount and frequency and directly controls net shortwave radiation receipt. In the context of modern glacier retreat on Kilimanjaro the results support other evidence that Kilimanjaro's glaciers are extremely sensitive to precipitation variability.

[1] High-elevation ice caps develop an archive of atmospheric constituents and properties through the accumulation of snowfall. The timing of precipitation events, therefore, fundamentally governs the environmental information that ice core records can provide. These events are often highly seasonal, as are various postdepositional processes influencing the snow's physical and chemical properties. Knowledge of climatic conditions at an ice core site is essential to a full understanding of the ice core record. This work reports on 4 years of meteorological measurements near the summit of Nevado Sajama, an ice-capped peak rising ∼2500 m above the South American Altiplano (elevation 6542 m), from which a 25,000-year ice core record was recovered in 1997. On-site measurements were combined with National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis results and Altiplano station data to reconstruct 50-year time series of air temperature, snowfall, and net accumulation at the summit. These time series were examined in the context of the Sajama δ18O profile over the same time interval. A strong relationship exists between Sajama δ18O and precipitation; both snowfall and net accumulation explain nearly half of the isotopic variance. In contrast, no significant association exists between air temperature and δ18O over this time period. The Sajama ice core record represents a relatively short proportion of time centered on the months of January or February, when net accumulation takes place, and cannot be interpreted in terms of annual mean conditions. On Sajama, interannual δ18O variability provides a sensitive measure of interannual precipitation variability, closely tied to ENSO and conditions in the equatorial Pacific Ocean.

matic records suggested that a more conventional temperature interpretation might be more appropriate, with lower isotopic values during the (presumed to be) cooler ‘‘Little Ice Age’’ and increasingly enriched precipitation during the 20th century warming phase [Thompson, 2001]. [3] Both of these conflicting interpretations suffer from inadequate calibration of the observed isotopic record, in relation to climatic conditions during periods of snow accumulation on the ice caps. Here, we use the results of on-site meteorological measurements to determine the seasonality of the ice core record, and then assess how the isotopic records relate to temperature, precipitation and the larger scale circulation associated with snowfall at these high elevation sites. We then extend the analysis to ice core records from the Asian monsoon region. This empirical approach to the interpretation of the isotopic record in low latitude ice cores complements theoretical studies by Broecker [1997] and Pierrehumbert [1999].

[1] We use the ECHAM-4 and the GISS II atmospheric general circulation models (AGCM) with incorporated stable isotopic tracers and forced with observed global sea surface temperatures (SST) between 1979 and 1998, to simulate the delta(18)O signal in three tropical Andean ice cores, from Huascaran (Peru), Quelccaya ( Peru), and Sajama ( Bolivia). In both models, the simulated stable isotopic records compare favorably with the observational data, when the seasonality of precipitation and dry season loss due to sublimation and wind scour are taken into account. Our simulations indicate a significant influence of the local climatic conditions (temperature and precipitation amount) on the delta(18)O signal. Moisture source variability appears to be less of a factor on interannual timescales. Even though the moisture originates over the Amazon basin and the tropical Atlantic, correlation fields with National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis atmospheric variables and SST data indicate a dominant tropical Pacific control on interannual timescales. More enriched (depleted) delta(18)O values are associated with periods of warm (cold) conditions in the tropical Pacific. This is consistent with modern observational evidence, which shows that climate and atmospheric circulation in the tropical Andes are closely correlated with SST anomalies in the tropical Pacific domain on interannual to interdecadal timescales. The growing number of stable isotope records from tropical Andean ice cores may thus provide an important archive for reconstructing Pacific climate variability.

[1] In the context of investigating modern glacier recession on Kilimanjaro, which began around 1880, this study addresses the glacier regime of the vertical ice walls that typically form the margins of Kilimanjaro’s summit glaciers. These walls have suffered a continuous lateral retreat during the twentieth century. To evaluate the role of solar radiation in maintaining glacier recession on Kilimanjaro, a radiation model is applied to an idealized representation of the 1880-ice cap. The combined process-based model calculates the spatial extent and geometry of the ice cap for various points in time after 1880. Support for input data and fundamental assumptions are provided by an automatic weather station that has operated on the summit’s Northern Icefield since February 2000. Even in a simple climatic scenario only forced with an annual cycle of clouds, the basic evolution in spatial distribution of ice bodies on the summit is modeled well. The Northern and Southern Icefields form in characteristic east-west orientation, which verifies the basic idea behind the model. Forcing the model with further climate-related phenomena improves the results. It then additionally reproduces the Eastern Icefield, the third big ice entity on the summit. This study qualitatively demonstrates that solar radiation is the main climatic parameter maintaining modern glacier recession on Kilimanjaro summit, but also suggests that retreat on the inner ice cap margin might have been supported by a secondary energy source. The need for additional field measurements is emphasized in order to better understand the complex processes of glacier-climate interaction on Kilimanjaro. INDEX TERMS: 1620 Global Change: Climate dynamics (3309); 1827 Hydrology: Glaciology (1863); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 9305 Information Related to Geographic Region: Africa; KEYWORDS: tropical glaciers, Kilimanjaro, climate change, glacier retreat, solar radiation modeling "#