Amanda H. Lynch

The Representation of Arctic Soils in the Land Surface Model: The Importance of Mosses

Mosses dominate the surface cover in high northern latitudes and have the potential to play a key role in modifying the thermal and hydrologic regime of Arctic soils. These modifications in turn feed back to influence surface energy exchanges and hence may affect regional climate. However, mosses are poorly represented in models of the land surface. In this study the NCAR Land Surface Model (LSM) was modified in two ways. First, additional soil texture types including mosses and lichens were added to more realistically represent northern soils. Second, the LSM was also modified so that a different soil texture type could be specified for each layer. Several experiments were performed using climate data from an Arctic tundra site in 1995. The model was run for a homogeneous loam soil column and then also for columns that included moss, lichen, peat, and sand. The addition of a surface layer of moss underlain by peat and loam had a substantial impact on modeled surface processes. First, moss acted as an insulative layer producing cooler summer temperatures (6.9 8C lower at 0.5 m) and warmer winter temperatures (2.38C higher at 0.5 m) when compared with a homogenous loam soil column. Second, a soil column with a moss surface had a greater surface infiltration, leading to greater storage of soil moisture in lower layers when compared with a homogeneous loam column. Last, moss modulated the surface energy exchanges by decreasing soil heat flux (57% in July) and increasing turbulent fluxes of heat (67% in July) and moisture (15% in July). Mosses were also more effective contributors to total latent heating than was a bare loam surface. These results suggest that the addition of moss and the ability to prescribe different soil textures for different soil layers result in a more plausible distribution of heat and water within the column and that these modifications should be incorporated into regional and global climate models.

Development of a Regional Climate Model of the Western Arctic

Abstract An Arctic region climate system model has been developed to simulate coupled interactions among the atmosphere, sea ice, ocean, and land surface of the western Arctic. The atmospheric formulation is based upon the NCAR regional climate model RegCM2, and includes the NCAR Community Climate Model Version 2 radiation scheme and the Biosphere–Atmosphere Transfer Scheme. The dynamic–thermodynamic sea ice model includes the Hibler–Flato cavitating fluid formulation and the Parkinson–Washington thermodynamic scheme linked to a mixed-layer ocean. Arctic winter and summer simulations have been performed at a 63 km resolution, driven at the boundaries by analyses compiled at the European Centre for Medium-Range Weather Forecasts. While the general spatial patterns are consistent with observations, the model shows biases when the results are examined in detail. These biases appear to be consequences in part of the lack of parameterizations of ice dynamics and the ice phase in atmospheric moist processes in ...

Summer Differences among Arctic Ecosystems in Regional Climate Forcing

Biome differences in surface energy balance strongly affect climate. However, arctic vegetation is considered sufficiently uniform that only a single arctic land surface type is generally used in climate models. Field measurements in northern Alaska show large differences among arctic ecosystem types in summer energy absorption and partitioning. Simulations with the Arctic Regional Climate System Model demonstrate that these variations in land surface parameters and ecological processes cause variation in surface fluxes that is sufficiently large to affect the regional climate. Plausible changes in arctic vegetation in response to high-latitude warming would feed back positively to local summer warming. This local warming could extend into the boreal zone. Climate feedbacks that operate during the growing season are particularly likely to impact vegetation and ecosystem properties. These field and model results suggest that vegetation changes within a biome could be climatically important and warrant consideration in regional climate modeling.

The Arctic Frontal Zone as Seen in the NCEP–NCAR Reanalysis

Abstract Calculations of a thermal front parameter using NCEP–NCAR reanalysis data over the period 1979–98 reveal a relative maximum in frontal frequencies during summer along northern Eurasia from about 60° to 70°N, best expressed over the eastern half of the continent. A similar relative maximum is found over Alaska, which is present year-round although best expressed in summer. These high-latitude features can be clearly distinguished from the polar frontal zone in the midlatitudes of the Pacific basin and collectively resemble the summertime“Arctic frontal zone” discussed in several early studies. While some separation between high- and midlatitude frontal activity is observed in all seasons, the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the Arctic Ocean coastline and associated wind maxima in the upper troposphere. The regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime...

Estimating the Uncertainty in a Regional Climate Model Related to Initial and Lateral Boundary Conditions

Abstract There is a growing demand for regional-scale climate predictions and assessments. Quantifying the impacts of uncertainty in initial conditions and lateral boundary forcing data on regional model simulations can potentially add value to the usefulness of regional climate modeling. Results from a regional model depend on the realism of the driving data from either global model outputs or global analyses; therefore, any biases in the driving data will be carried through to the regional model. This study used four popular global analyses and achieved 16 driving datasets by using different interpolation procedures. The spread of the 16 datasets represents a possible range of driving data based on analyses to the regional model. This spread is smaller than typically associated with global climate model realizations of the Arctic climate. Three groups of 16 realizations were conducted using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale M...

Australian East-Coast Cyclones. Part I: Synoptic Overview and Case Study

Abstract The meteorological conditions for the development of Australian east-coast cyclones are described. The main synoptic precursor is a trough (or “dip”) in the easterly wind regime over eastern Australia. The cyclones are a mesoscale development which occurs on the coast in this synoptic environment. They form preferentially at night, in the vicinity of a marked low-level baroclinic zone, and just equatorward of a region of enhanced convection resulting from flow over the coastal ranges. Three different types of east-coast cyclone have been identified. Types 1 and 3 are very small systems which can have lifetimes as short as 16 hours, during which hurricane force winds have been observed to develop. The other, type 2, system is a meso/synoptic-scale cyclone that can bring sustained strong winds and flood rainfall over several days. Because of their intensity, rapid development, and occasional tiny size, these systems are a major forecast problem.

WORKING AT THE BOUNDARY Facilitating Interdisciplinarity in Climate Change Adaptation Research

Abstract Efforts are being made to develop new paradigms for climate change adaptation policy at both the national and the international levels. However, progress in vulnerability and adaptation research has not been matched by advancement on practical policy initiatives. The complexity of the challenge to develop methods and means to support adaptation to climate change necessitates a diversity of approaches. This diversity is healthy, and yet it is possible to define some key characteristics and tools that can promote practical outcomes. In this paper, some methodologies that have proved successful are reviewed. These include a mapping of contextual circumstances, an appreciation for multiple perspectives, and the importance of a “boundary object” in forging strong interactions among project participants. Further, a toolkit of approaches for natural scientists is presented. This toolkit can be used to organize work in collaboration with stakeholders and other participants and can help overcome barriers ...

Impact of tundra ecosystems on the surface energy budget and climate of Alaska

The sensitivity of regional terrestrial climate to the characteristics of tundra ecosystems has been investigated by a series of sensitivity experiments concentrating on the summer of 1995. Validation of the NCAR Land Surface Model and the Arctic Regional Climate System Model for this season indicate their adequacy for this study. Comparisons of the simulated climate in response to a wet meadow tundra or a dry heath tundra results in an expected cooling and moistening of both the local area and the adjoining sea ice and forested regions. The impact of atmospheric cloud-radiation feedbacks is to reduce the cooling as the summer progresses, although moistening continues, associated with increased precipitation in some areas. The spatial variability of the response is dependent upon prevailing synoptic conditions, which act to enhance moisture advection in certain areas. This study indicates that vegetation variation within the Arctic has substantial climatic effects that extend beyond the Arctic. In addition, the perturbations in the summer season could have profound implications of Arctic wintertime climate and issues of snow-albedo feedback and spring melt.

Comparing Arctic Regional Climate Model

Recent climate modeling results show the Arctic to be a region of particular importance and vulnerability to global climate change. Despite the climatic significance of the Arctic, many physical processes occurring in this region are still not well understood. Hence, it is not surprising that simulated climates of the Arctic vary widely depending on the choice of climate model and physical parameterizations.

Snow‐albedo feedback and the spring transition in a regional climate system model: Influence of land surface model

Using the Arctic regional climate system model (ARCSYM), we investigate the spring seasonal transition and mechanisms controlling snowmelt over a domain covering the northern half of Alaska. Annual simulations for 1992 comparing the Biosphere-Atmosphere Transfer Scheme (BATS) and the land surface model scheme (LSM) show that the BATS experiment enters the spring transition with respect to the large-scale atmospheric regime approximately one month earlier than observed climate and the LSM experiment transitions a month later than observed, even though the air temperature in the LSM experiment is generally warmer than in the BATS experiment. A more detailed examination reveals that each simulation commences and completes the snowmelt period at about the same time but that the LSM snowmelt is more rapid than in the BATS experiment. Controlling the snowmelt is the initial snowpack depth and the surface energy budget, both of which involve a complex series of feedbacks between shortwave and longwave radiation, cloud, surface turbulent fluxes, and vegetation. The snowmelt over tundra regions dominates the more rapid snowmelt seen in the LSM simulation. It is determined that the most crucial differences between the BATS and the LSM schemes are the partitioning of net ground heat flux between patches of snow and bare ground and the formulation of snow albedo.