Annette Rinke

Vulnerability of permafrost carbon to climate change: Implications for the global carbon cycle

ABSTRACT Thawing permafrost and the resulting microbial decomposition of previously frozen organic carbon (C) is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. In this article we present an overview of the global permafrost C pool and of the processes that might transfer this C into the atmosphere, as well as the associated ecosystem changes that occur with thawing. We show that accounting for C stored deep in the permafrost more than doubles previous high-latitude inventory estimates, with this new estimate equivalent to twice the atmospheric C pool. The thawing of permafrost with warming occurs both gradually and catastrophically, exposing organic C to microbial decomposition. Other aspects of ecosystem dynamics can be altered by climate change along with thawing permafrost, such as growing season length, plant growth rates and species composition, and ecosystem energy exchange. However, these processes do not appear to be able to compensate for C release from thawing permafrost, making it likely that the net effect of widespread permafrost thawing will be a positive feedback to a warming climate.

Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation

ABSTRACT The response of the Arctic atmosphere to low and high sea ice concentration phases based on European Center for Medium-Range Weather Forecast (ECMWF) Re-Analysis Interim (ERA-Interim) atmospheric data and Hadley Centres sea ice dataset (HadISST1) from 1989 until 2010 has been studied. Time slices of winter atmospheric circulation with high (1990–2000) and low (2001–2010) sea ice concentration in the preceding August/September have been analysed with respect to tropospheric interactions between planetary and baroclinic waves. It is shown that a changed sea ice concentration over the Arctic Ocean impacts differently the development of synoptic and planetary atmospheric circulation systems. During the low ice phase, stronger heat release to the atmosphere over the Arctic Ocean reduces the atmospheric vertical static stability. This leads to an earlier onset of baroclinic instability that further modulates the non-linear interactions between baroclinic wave energy fluxes on time scales of 2.5–6 d and planetary scales of 10–90 d. Our analysis suggests that Arctic sea ice concentration changes exert a remote impact on the large-scale atmospheric circulation during winter, exhibiting a barotropic structure with similar patterns of pressure anomalies at the surface and in the mid-troposphere. These are connected to pronounced planetary wave train changes notably over the North Pacific.

Regional climate model of the Arctic atmosphere

A regional climate model of the whole Arctic using the dynamical package of the High- Resolution Limited Area Model (HIRLAM) and the physical parameterizations of the Hamburg General Circulation Model (ECHAM3) has been applied to simulate the climate of the Arctic north of 65 oN at a 50-km horizontal resolution. The model has been forced by the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses at the lateral boundaries and with climatological or actual observed sea surface temperatures and sea ice cover at the lower boundary. The results of simulating the Arctic climate of the troposphere and lower stratosphere for January 1991 and July 1990 have been described. In both months the model rather closely reproduces the observed monthly mean circulation. While the general spatial patterns of surface air temperature, mean sea level pressure, and geopotential are consistent with the ECMWF analyses, the model shows biases when the results are examined in detail. The largest biases appear during winter in the planetary boundary layer and at the surface. The underestimated vertical heat and humidity transport in the model indicates the necessity of improvements in the parameterizations of vertical transfer due to boundary layer processes. The tropospheric differences between model simulations and analyses decrease with increasing height. The temperature bias in the planetary boundary layer can be reduced by increasing the model sea ice thickness. The use of actual observed sea surface temperatures and sea ice cover leads only to small improvements of the model bias in comparison with climatological sea surface temperatures and sea ice cover. The validation of model computed geopotential, radiative fluxes, surface sensible and latent heat fluxes and clouds against selected station data shows deviations between model simulations and observations due to shortcomings of the model. This first validation indicates that improvements in the physical parameterization packages of radiation and in the description of sea ice thickness and sea ice fraction are necessary to reduce the model bias.

Recent Greenland Accumulation Estimated from Regional Climate Model Simulations and Ice Core Analysis

Abstract The accumulation defined as “precipitation minus evaporation” over Greenland has been simulated with the high-resolution limited-area regional climate model HIRHAM4 applied over an Arctic integration domain. This simulation is compared with a revised estimate of annual accumulation rate distribution over Greenland taking into account information from a new set of ice core analyses, based on surface sample collections from the North Greenland Traverse. The region with accumulation rates below 150 mm yr−1 in central-northwest Greenland is much larger than previously assumed and extends about 500 km farther to the south. It is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists, particularly concerning the location and the values of very low accumulation in the middle of Greenland. The accumulation rates in the northern part of Greenland are reduced in comparison to previous estimates. These minima are connected with a prevailing bloc...

A dynamical link between the Arctic and the global climate system

Received 16 November 2005; revised 12 December 2005; accepted 15 December 2005; published 1 February 2006. [1] By means of simulations with a global coupled AOGCM it is shown that changes in the polar energy sink region can exert a strong influence on the mid- and high-latitude climate by modulating the strength of the mid-latitude westerlies and storm tracks. It is found, that a more realistic sea-ice and snow albedo treatment changes the ice-albedo feedback and the radiative exchange between the atmosphere and the ocean-sea-ice system. The planetary wave energy fluxes in the middle troposphere of mid-latitudes between 30 and 50 Na re redistributed, which induces perturbations in the zonal and meridional planetary wave trains from the tropics over the mid-latitudes into the Arctic. It is shown, that the improved parameterization of Arctic sea-ice and snow albedo can trigger changes in the Arctic and North Atlantic Oscillation pattern with strong implications for the European climate. Citation: Dethloff, K., et al. (2006), A dynamical link between the Arctic and the global climate system, Geophys. Res. Lett., 33, L03703, doi:10.1029/2005GL025245.

Evaluation of Greenland ice sheet surface climate in the HIRHAM regional climate model using automatic weather station data

The 1998 annual cycle and 1991‐98 summer simulations of Greenland ice sheet surface climate are made with the 0.58-horizontal resolution HIRHAM regional climate model of the Arctic. The model output is compared with meteorological and energy balance observations from 15 Greenland Climate Network automatic weather stations. The model reproduces the monthly average surface climate parameters, to a large extent within model and observational uncertainty. However, certain systematic model biases were identified, caused in particular by inaccurate GTOPO30 elevation data over Greenland, 180 m lower on average, with errors as large as 2840 m over 50-km grid cells. The resulting warm biases enhance a negative albedo bias, which in turn leads to positive net shortwave radiation biases. Surface sensible and latent heat fluxes are overestimated, apparently due to model warm bias and 100% greater than observed wind speeds. Interannual variability in temperature and albedo are smaller in the model than in the observations, while the opposite is evident for incoming shortwave radiation and wind speed. Annual maps and total mass fluxes of precipitation and evaporation are compared with results from other studies. Based on the results of a multiparameter comparison, solid recommendations for improved regional models of ice sheet climate are made.

Sensitivity of Arctic climate simulations to different boundary-layer parameterizations in a regional climate model

Arctic climate simulations with the high resolution regional climate model HIRHAM showsome deviations from station data in the planetary boundary layer (PBL) during winter, whichindicates the necessity of improvements in the atmospheric PBL parameterization for a betterdescription of the vertical stratification and atmosphere–surface energy exchange. A1-dimensional single column model scheme has been used to investigate the influence of twodifferent PBL parameterizations in monthly integrations for January 1991 and July 1990. Thefirst scheme uses the boundary layer parameterization of the atmospheric circulation modelECHAM3, including the Monin–Obukhov similarity theory in the surface layer and a mixinglength approach above. The second scheme applies the Rossby-number similarity theory forthe whole PBL, connecting external parameters with turbulent fluxes and with universal functionsdetermined on the basis of Arctic data. For both schemes the heat and humidity advectionhas been determined as residual term of the PBL balance equations. Diabatic sources havebeen computed from the current model solution and local temperature and humidity changesare estimated from radiosonde data. The simulated vertical structure and the atmosphere–surface energy exchange during January strongly depends on the used PBL parameterizationscheme. These different PBL parameterization schemes were then applied for simulations of theArctic climate in the 3-dimensional regional atmospheric climate model HIRHAM, usingECHAM3 with Monin–Obukhov similarity theory, ECHAM3 with Rossby-number similaritytheory and ECHAM4 parameterizations with a turbulent kinetic energy closure. The nearsurface temperature, the large-scale fields of geopotential and horizontal wind are simulatedsatisfactorily by all three schemes, but strong regional differences occur. The results show asensitivity to the type of turbulence exchange scheme used. The comparison with ECMWFanalyses and with radiosonde data reveals that during January ECHAM3 with Rossby numbersimilarity theory more succesfully simulates the cold and stable PBL over land surfaces, whereasover the open ocean ECHAM3 with Monin Obukhov similarity works better. ECHAM3 withRossby-number similarity theory delivers a better adapted vertical heat exchange under stableArctic conditions and reduces the cold bias at the surface. The monthly mean surface turbulentheat flux distribution strongly depends on the use of different PBL parameterizations and leadsto different Arctic climate structures throughout the atmosphere with the strongest changes atthe ice edge for January.

Winter Weather Patterns over Northern Eurasia and Arctic Sea Ice Loss

AbstractUsing NCEP–NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) winter daily (1 December–28 February) data for the period 1979–2012, this paper reveals the leading pattern of winter daily 850-hPa wind variability over northern Eurasia from a dynamic perspective. The results show that the leading pattern accounts for 18% of the total anomalous kinetic energy and consists of two subpatterns: the dipole and the tripole wind patterns. The dipole wind pattern does not exhibit any apparent trend. The tripole wind pattern, however, has displayed significant trends since the late 1980s. The negative phase of the tripole wind pattern corresponds to an anomalous anticyclone over northern Eurasia during winter, as well as two anomalous cyclones occurring over southern Europe and in the mid- to high latitudes of East Asia. These anomalous cyclones in turn lead to enhanced winter precipitation in these two regions, as well as negative surface temperature anomalies over the mid- to high latitudes of Asia. The...

Simulation and validation of Arctic radiation and clouds in a regional climate model

A regional atmospheric climate model has been applied to simulate the Arctic climate north of 65N at a 50 kmhorizontal resolution for January and July 1990. The monthly mean components of the surface radiative balanceand clouds using ECHAM3 parameterization have been described and compared with data. The modeloverestimates the global radiation, overestimates clouds during January and underestimates clouds during July.The high resolution simulations show many regional details due to regional different surface temperatures, clouds, surface albedo and snow depths. The bias in the model simulation can be reduced by using the improvedECHAM4 parameterization. The use of the ECHAM4 radiation parameterization clearly improves the results,owing the better description of atmospheric absorption. Sensitivity expe-riments with different cloud parametershave been described.

Variability in the sensitivity among model simulations of permafrost and carbon dynamics in the permafrost region between 1960 and 2009

A significant portion of the large amount of carbon (C) currently stored in soils of the permafrost region in the Northern Hemisphere has the potential to be emitted as the greenhouse gases CO2 and CH4 under a warmer climate. In this study we evaluated the variability in the sensitivity of permafrost and C in recent decades among land surface model simulations over the permafrost region between 1960 and 2009. The 15 model simulations all predict a loss of near-surface permafrost (within 3 m) area over the region, but there are large differences in the magnitude of the simulated rates of loss among the models (0.2 to 58.8 × 103 km2 yr−1). Sensitivity simulations indicated that changes in air temperature largely explained changes in permafrost area, although interactions among changes in other environmental variables also played a role. All of the models indicate that both vegetation and soil C storage together have increased by 156 to 954 Tg C yr−1 between 1960 and 2009 over the permafrost region even though model analyses indicate that warming alone would decrease soil C storage. Increases in gross primary production (GPP) largely explain the simulated increases in vegetation and soil C. The sensitivity of GPP to increases in atmospheric CO2 was the dominant cause of increases in GPP across the models, but comparison of simulated GPP trends across the 1982–2009 period with that of a global GPP data set indicates that all of the models overestimate the trend in GPP. Disturbance also appears to be an important factor affecting C storage, as models that consider disturbance had lower increases in C storage than models that did not consider disturbance. To improve the modeling of C in the permafrost region, there is the need for the modeling community to standardize structural representation of permafrost and carbon dynamics among models that are used to evaluate the permafrost C feedback and for the modeling and observational communities to jointly develop data sets and methodologies to more effectively benchmark models. (Less)