Arctic Observations Research Articles

Intrinsic versus Forced Variation in Coupled Climate Model Simulations over the Arctic during the Twentieth Century*

Abstract There were two major multiyear, Arctic-wide (60°–90°N) warm anomalies (>0.7°C) in land surface air temperature (LSAT) during the twentieth century, between 1920 and 1950 and again at the end of the century after 1979. Reproducing this decadal and longer variability in coupled general circulation models (GCMs) is a critical test for understanding processes in the Arctic climate system and increasing the confidence in the Intergovernmental Panel on Climate Change (IPCC) model projections. This study evaluated 63 realizations generated by 20 coupled GCMs made available for the IPCC Fourth Assessment for their twentieth-century climate in coupled models (20C3M) and corresponding control runs (PIcntrl). Warm anomalies in the Arctic during the last two decades are reproduced by all ensemble members, with considerable variability in amplitude among models. In contrast, only eight models generated warm anomaly amplitude of at least two-thirds of the observed midcentury warm event in at least one realization, but not its timing. The durations of the midcentury warm events in all the models are decadal, while that of the observed was interdecadal. The variance of the control runs in nine models was comparable with the variance in the observations. The random timing of midcentury warm anomalies in 20C3M simulations and the similar variance of the control runs in about half of the models suggest that the observed midcentury warm period is consistent with intrinsic climate variability. Five models were considered to compare somewhat favorably to Arctic observations in both matching the variance of the observed temperature record in their control runs and representing the decadal mean temperature anomaly amplitude in their 20C3M simulations. Seven additional models could be given further consideration. Results support selecting a subset of GCMs when making predictions for future climate by using performance criteria based on comparison with retrospective data.

An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.

An array of ice‐based observatories for Arctic studies

The Arctic Ocean's role in global climate—while now widely appreciated—remains poorly understood. Lack of information about key processes within the oceanic, cryospheric, biologic, atmospheric, and geologic disciplines will continue to impede physical understanding, model validation, and climate prediction until a practical observing system is designed and implemented.A review of recently observed changes in the physical and biological state of the Arctic and a justification for future Arctic observations are contained in the supporting document of the U.S. National Science Foundation's (NSF) “Study of Environmental Arctic Change” program (SEARCH, http://psc.apl.washington.edu/search/). Comparable Arctic study programs have been conceived as an international contribution to the proposed International Polar Year 2007–2008 (http://www.aosb.org/ipyhtml). Future directions in instrument development for Arctic studies were also considered at a workshop at the Monterey Bay Aquarium Research Institute in October 2002 (http://www.mbari.org/rd/ArcticInstrumentationWorkshop).

High Arctic observations of mesospheric inversion layers

Rayleigh lidar measurements of middle atmospheric temperatures obtained in the High Arctic at Eureka (80°N, 86°W) are examined for evidence of mesospheric inversion layers with overlying nearly‐adiabatic lapse rates. Inversion layers are identified in 5.4 ± 0.5% of the measurements, a rate considerably lower than is observed at midlatitudes. The altitude distribution for the Arctic inversions is similar to that found at midlatitudes. No phase progression or relationship with stratospheric gravity wave activity was found. The observations have important consequences for theories of the mesospheric inversion layer.

Dehydration in the Arctic stratosphere during the SOLVE/THESEO‐2000 campaigns

Balloon‐borne measurements of H2O, CH4, and H2 in January and March 2000 show clear evidence for dehydration inside the polar vortex. At 30–50 hPa, total hydrogen is reduced by approximately 0.5 ppmv. This phenomenon is apparent in all five in situ balloon observations of this period; therefore it is probable that dehydration occurred over extended regions and a long period of this winter which was characterized by a well‐confined vortex and low stratospheric temperatures. At altitudes below 50 hPa, where dehydration was strongest in previous Arctic observations and in the austral spring, total hydrogen values (2·CH4 + H2O + H2) were similar to those found in Arctic profiles from other years where there was no dehydration and to those found at midlatitudes. In some of the dehydrated air masses, small solid particles were found whose crystallization might be connected to the earlier formation of ice particles. Back trajectory calculations for the January observations indicate that the probed air masses had experienced temperatures below the ice frost point in a synoptic‐scale cold region several days before the observations. Most likely, the air was dehydrated there. In addition, temperatures in these air masses dropped below ice saturation several hours prior to the observations in the lee of the Scandinavian mountain ridge. For the March measurements, no ice saturation was apparent in the recent history of the air masses, again indicating that dehydration in the Arctic winter 1999/2000 was not a local phenomenon.

Arctic and Antarctic ozone layer observations: chemical and dynamical aspects of variability and long-term changes in the polar stratosphere

The altitude dependent variability of ozone in the polar stratosphere is regularly observed by balloon-borne ozonesonde observations at Neumayer Station (70°S) in the Antarctic and at Koldewey Station (79°N)in the Arctic. The reasons for observed seasonal and interannual variability and long-term changes are discussed. Differences between the hemispheres are identified and discussed in light of differing dynamical and chemical conditions. Since the mid- 1980s, rapid chemical ozone loss has been recorded in the lower Antarctic stratosphere during the spring season. Using coordinated ozone soundings in some Arctic winters, similar chemical ozone loss rates have been detected related to periods of low temperatures. The currently observed cooling trend of the stratosphere, potentially caused by the increase of anthropogenic greenhouse gases, may further strengthen chemical ozone removal in the Arctic. However, the role of internal climate oscillations in observed temperature trends is still uncertain. First results of a 10000 year integration of a low order climate model indicate significant internal climate variability. on decadal time scales, that may alter the effect of increasing levels of greenhouse gases in the polar stratosphere.

Polar stratospheric descent of NOy and CO and Arctic denitrification during winter 1992–1993

Observations inside the November 1994 Antarctic stratospheric vortex and inside the April 1993 remnant Arctic stratospheric vortex by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer are reported. In both instances, elevated volume mixing ratios (VMRs) of carbon monoxide (CO) were measured. A peak Antarctic CO VMR of 60 ppbv (where 1 ppbv = 10−9 per unit volume) was measured at a potential temperature (Θ) of 710 K (∼27 km), about 1 km below the altitude of a pocket of elevated NOy (total reactive nitrogen) at a deep minimum in N2O (<5 ppbv). The Arctic observations also show a region of elevated vortex CO with a peak VMR of 90 ppbv at 630–670 K (∼25 km) but no corresponding enhancement in NOy, perhaps because of stronger dynamical activity in the northern hemisphere polar winter and/or interannual variability in the production of mesospheric or lower thermospheric NO. By comparing vortex and extravortex observations of NOy obtained at the same N2O VMR, Arctic vortex denitrification of 5 ± 2 ppbv at 470 K (∼18 km) is inferred. We show that our conclusion of substantial Arctic winter 1992–1993 denitrification is robust by comparing our extravortex observations with previous polar measurements obtained over a wide range of winter conditions. Correlations of NOy with N2O measured at the same Θ by ATMOS in the Arctic vortex and at midlatitudes on board the ER‐2 aircraft several weeks later lie along the same mixing line. The result demonstrates the consistency of the two data sets and confirms that the ER‐2 sampled fragments of the denitrified Arctic vortex following its breakup. An analysis of the ATMOS Arctic measurements of total hydrogen shows no evidence for significant dehydration inside the vortex.

Rayleigh lidar system for middle atmosphere research in the arctic

A Rayleigh/Mie lidar system deployed at the Sondrestrom At- mospheric Research Facility located on the west coast of Greenland near the town of Kangerlussuaq (67.0 deg N, 50.9 deg W) has been in operation since 1993 making unique observations of the arctic middle atmosphere. The vertically directed lidar samples the elastically back- scattered laser energy from molecules (Rayleigh) and aerosols (Mie) over the altitude range from 15 to 90 km at high spatial resolution. The limited amount of arctic observations of the middle atmosphere currently available emphasizes the importance and utility of a permanent Rayleigh lidar system in Greenland. The lidar system consists of a frequency- doubled, 17-W Nd:YAG laser at 532 nm, a 92 cm Newtonian telescope, and a two-channel photon counting receiver. The principal objective of the lidar project is to contribute to studies concerned with the climatology and phenomenology of the arctic middle atmosphere. To this end, we describe the lidar system in detail, evaluate system performance, de- scribe data analysis, and discuss the system capabilities in determining the density, temperature, and the presence of aerosols in the arctic middle atmosphere. Particular emphasis is placed on the derivation of temperature from the lidar measurement and on the impact of signal- induced noise on this analysis. Also, we develop a statistical filter based on a Bayesian approach to optimally smooth the lidar profile in range. This filter preserves the short-term fluctuations in the low-altitude data consisting of relatively high SNR, whereas more smoothing is applied to the high-altitude data as the SNR decreases. © 1997 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(97)01607-3)

The Arctic polar stratospheric cloud aerosol: Aircraft measurements of reactive nitrogen, total water, and particles

The reactive nitrogen (NOy), total water, and particle components of the polar stratospheric cloud (PSC) aerosol in the Arctic are studied using in situ aircraft measurements in the lower stratosphere. The results are compared to findings from the Antarctic derived using similar measurements and interpretive techniques. The Arctic data show that particle volume well above background values is present at temperatures above the frostpoint, confirming the result from the Antarctic that the observed PSC's are not water ice particles. NOy measurements inside a PSC are enhanced above ambient values consistent with anisokinetic sampling of particles containing NOy. Furthermore, relative changes in the measured particle volume along a flight track are well correlated with changes in the amount of NOy estimated to be in the particle phase. With the exception of data from one flight, assuming that the composition of the PSC particles is nitric acid trihydrate (NAT), the HNO3 content of the measured particle volume is consistent with the amount of HNO3 predicted to be available for condensation. To this extent, the Arctic observations are consistent with NAT as the composition of PSC particles, in agreement with the Antarctic findings. In the Arctic data over long segments of several flights, calculations show saturation with respect to NAT without significant PSC particle growth above background. PSCs in the Arctic are not observed in situ until the apparent saturation ratio of HNO3 with respect to NAT is greater than 10, in marked contrast to the Antarctic, where PSCs are observed in conditions of apparent HNO3 saturation of 1 and above. This difference cannot be resolved by known measurement uncertainties. Also, a discrepancy is noted in the comparison of the amount of condensed HNO3 derived from the particle distribution measurements with that derived from the NOy measurements, assuming a NAT composition for the particles. Although the relative variations in the derived quantities are similar, as in the Antarctic, the mean values consistently disagree by about a factor of 2. The differences suggest that there may be systematic errors in the data and/or physical assumptions used in the analysis. Several possibilities are discussed.

Ozone and other trace gases in the Arctic and Antarctic regions: Three‐dimensional model simulations

A three‐dimensional mechanistic model of the middle atmosphere with calculated dynamics and chemistry (Rose and Brasseur, 1989) is used to study the behavior of chemically active trace gases at high latitudes in winter and spring, and to simulate the formation of an ozone hole in Antarctica. The dynamics of both hemispheres is simulated by applying at the lower boundary of the model (8.5 km) a wavelike perturbation representing qualitatively a climatological tropospheric forcing. The chemical heterogeneous processes converting chlorine reservoirs into active chlorine in cold air masses are parameterized. The model simulates the behavior of nitrogen oxides, nitric acid, water vapor, methane, hydrogen radicals, chlorine compounds, and ozone. It reproduces important features observed during different Antarctic and Arctic observation campaigns. The ozone hole in the southern hemisphere can only be simulated when the heterogeneous polar chemistry is taken into account. The springtime ozone depletion over Antarctica calculated in the model is thus mostly the result of chemical removal although the dynamics is responsible for the low temperature that triggers the large ozone loss rates. Unresolved questions are related to the strength of the vertical exchanges inside the vortex, the preconditioning of trace gases before and during the winter season, the behavior of the different trace gases as the vortex breaks down (dilution effects), accurate determination of the ozone sink inside the vortex, and a better quantitative estimation of the role of polar stratospheric clouds. Despite elevated concentrations of active chlorine at high latitudes in the northern hemisphere in late winter, no ozone hole is produced by the model, even with chlorine levels as high as 6 ppbv. This conclusion could, however, be modified for very stable and cold winters with delayed final warming.

Ozone variations in the Northern polar region

All total ozone observations ever made in the Northern polar region, including some from the 1930's, have been corrected and the basic climatology presented. The long-term ozone changes were considered in relation to the stratospheric temperatures. For each deviation from the monthly normal of the 100 hPa temperature by 1°C, there was found to be a corresponding 5–6 m atm-cm change in the monthly ozone deviation. A distinction between the ozone regimes over the Scandinavian, Canadian and East Siberian sectors of the polar region was noted. The strong appearance of the QBO (Quasi Biennial Oscillation) in the interannual ozone fluctuations was obvious. It is demonstrated that for the past three decades the total ozone experienced a few periods with positive and a few periods with negative deviations. In view of this, trends in ozone must obviously be based on greater than 10 years of data. During 1964–86, the weighted trend over the polar stations was (−0.9±0.4)% per decade. There have been, however, three periods (1958–64, 1968–76 and 1979–86), coinciding with the declining phase of the 11 year sunspot cycle, during which the ozone at all polar stations has been declining by about 0.5% per year (or less if the QBO component is filtered out). Some of the differences with Antarctic ozone are mentioned and the dominant role of the stratospheric circulation for the ozone variations is discussed. In general the Arctic ozone observations show no evidence of a major ozone decline similar to that over Antarctica.

Studies of Patterned Ground on SW Devon Island, N. W. T. A Method for Collecting Undisturbed Megasamples from Dry Arctic Polygons and Observations on Some Physical Properties of the Material in a Sorted Polygon

Studies of Patterned Ground on SW Devon Island, N. W. T. A Method for Collecting Undisturbed Megasamples from Dry Arctic Polygons and Observations on Some Physical Properties of the Material in a Sorted Polygon

Arctic Air Route Observations in Greenland, 1935–36

<i>Arctic Air Route Observations in Greenland</i>, 1935–36

Shufeldt's Recent Contributions to the Osteology of North American Birds Contributions to the Comparative Osteology of Arctic and Sub-Arctic Water-Birds Shufeldt Observations upon the Osteology of the North American Anseres Shufeldt Osteological Studies of the Subfamily Ardeinæ Shufeldt Observations upon the Osteology of the Orders Tubinares and Steganopodes Shufeldt

Shufeldt's Recent Contributions to the Osteology of North American Birds Contributions to the Comparative Osteology of Arctic and Sub-Arctic Water-Birds Shufeldt Observations upon the Osteology of the North American Anseres Shufeldt Osteological Studies of the Subfamily Ardeinæ Shufeldt Observations upon the Osteology of the Orders Tubinares and Steganopodes Shufeldt

Magnetic and Auroral Observations in High Latitudes

LIEUTENANT WEYPRECHT, the noted leader of the Austrian Arctic Expedition of 1872-74, whose death is a great loss to science, recently published a little text-book embodying the results of his wide experience in Arctic observation of magnetic and auroral phenomena, which will be invaluable in pointing out to future observers the precautions and requirements which only actual experience of Arctic life can suggest, and the arrangements of apparatus and stores, which, once left behind, must be done without; frequently to the loss of opportunities for observation which do not recur. It would however be wearisome to the general reader to enter into details of Arctic work, and no one to whom the matter is of practical moment will omit reading the book itself. Some however of the precautions suggested give so vivid an idea of the difficulties and even the suffering which Arctic observers have to meet in the cause of science, that we cannot forbear a passing mention of them.