Search

High elevations are thought to be warming more rapidly than lower elevations, but there is a lack of air temperature observations in high mountains. This study compares instantaneous values of land surface temperature (1030/2230 and 0130/1330 local solar time) as measured by MODIS MOD11A2/MYD11A2 at 1 km resolution from the TERRA and AQUA platforms respectively with equivalent screen level air temperatures (in the same pixel). We use a transect of 22 in situ weather stations across Kilimanjaro ranging in elevation from 990 to 5803 m, one of the biggest elevational ranges in the world. There are substantial differences between LST and Tair, sometimes up to 20˚C. During the day/night LST tends to be higher/lower than Tair. LST-Tair differences (ΔT) show large variance, particularly during the daytime, and tend to increase with elevation, particularly on the NE slope which faces the morning sun. Differences are larger in the dry seasons (JF and JJAS), and reduce in cloudy seasons. Healthier vegetation (as measured by NDVI) and increased humidity lead to reduced daytime surface heating above air temperature and lower ΔT, but these relationships weaken with elevation. At high elevations transient snow cover cools LST more than Tair. The predictability of ΔT therefore reduces. It will therefore be challenging to use satellite data at high elevations as a proxy for in situ air temperatures in climate change assessments, especially for daytime Tmax. ΔT is smaller and more consistent at night, so it will be easier to use LST to monitor changes in Tmin.

Subarctic Scandinavia is expected to experience significant temperature increases over the next century. How this increase will influence local scale climate is largely unknown. This study examines local scale temperature variability in the subarctic where the unusual solar geometry means that the classic diurnal cycle of mid-latitudes has limited application.Near surface air temperature data were collected from a high density network of 60 temperature data loggers covering approximately 20 km2 in the valley system around Kevo Subarctic Research Station (69°45′N, 27°1′E). Temperature data was collected at 30 min intervals from September 2007 to March 2010, along with additional temperature and cloud cover data from the Kevo station. NCEP/NCAR reanalysis data was used to reconstruct synoptic conditions for the area at 6-h intervals. Lapse rates and regression of surface temperatures on free air temperatures are used to investigate local temperature variability. Median absolute yearly deviation analysis of the site temperatures was used to assess the representativeness of Kevo Station.The results show intense (up to + 80 °C km−1) and persistent inversion events during the winter months (NDJ) which are broken up by mechanical effects. In the transition from winter into spring (FMA) these inversions still occur but increasing radiation imposes a diurnal pattern on their formation and destruction. As snow cover peaks in spring the interaction between surface albedo, land cover and radiation serves to amplify the diurnal cycle in lapse rates. Summer lapse rates are modified by the presence of open water at low elevations. These results suggest that expected land cover and synoptic changes due to regional warming will act to decrease the frequency and intensity of inversion formation, steepening mean lapse rates and therefore increasing the relative amount of warming in valley floor locations.

The Tibetan Plateau (TP) with an average elevation of over 4000 m a.s.l. is the world's highest and most extensive highland. The scarcity of climatic observations limits our understanding of surface air temperature change in the region. Thus, we compare temperatures and their trends from 71 homogenized surface stations (with elevations above 2000 m a.s.l.) with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis (NCEP/NCAR hereafter) and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-40 hereafter) in the eastern and central TP during 1961–2004. For current climatology, ERA-40 is more similar to the surface stations than NCEP/NCAR. Compared with surface stations, both NCEP/NCAR and ERA-40 reanalyses have cold biases, which are mainly a result of differences in topographical height, and station aspect and slope. Warming trends at the surface stations are on average stronger than in both reanalyses, but ERA-40 captures the surface warming more clearly than NCEP/NCAR on an annual and seasonal basis. Since ERA-40 more closely represents the surface temperatures and their trends in the central and eastern TP, ERA-40 predictions are selected to examine change in the western TP where there are few surface stations. NCEP/NCAR, on the other hand, is more representative of free air temperature conditions. The ‘observation minus reanalysis’ (OMR) method can be used to estimate the impact of surface changes on climate by computing the difference between surface observations and NCEP/NCAR (which only contains the forcing influencing the assimilated atmospheric trends). The OMR trend is significantly increasing but the extent to which the changes in local environment are responsible needs further study. Copyright © 2012 Royal Meteorological Society

Global warming has created a need for studies along climatic gradients to assess the effects of temperature on ecological processes. Altitudinal and latitudinal gradients are often used as such, usually in combination with air temperature data from the closest weather station recorded at 1.52 m above the ground. However, many ecological processes occur in, at, or right above the soil surface. To evaluate how representative the commonly used weather station data are for the microclimate relevant for soil surface biota, we compared weather station temperatures for an altitudinal (500900 m a.s.l.) and a latitudinal gradient (4968 degrees N) with data obtained by temperature sensors placed right below the soil surface at five sites along these gradients. The mean annual temperatures obtained from weather stations and adjusted using a lapse rate of -5.5 degrees C km-1 were between 3.8 degrees C lower and 1.6 degrees C higher than those recorded by the temperature sensors at the soil surface, depending on the position along the gradients. The monthly mean temperatures were up to 10 degrees C warmer or 5 degrees C colder at the soil surface. The within-site variation in accumulated temperature was as high as would be expected from a 300 m change in altitude or from a 4 degrees change in latitude or a climate change scenario corresponding to warming of 1.63.8 degrees C. Thus, these differences introduced by the decoupling are significant from a climate change perspective, and the results demonstrate the need for incorporating microclimatic variation when conducting studies along altitudinal or latitudinal gradients. We emphasize the need for using relevant temperature data in climate impact studies and further call for more studies describing the soil surface microclimate, which is crucial for much of the biota.

The Tibetan Plateau (TP) has the largest area of snow in the mid-latitude regions, and is strongly affected by the climate change. We examine the temporal variability of winter snow depth and number of days of snow cover at 69 Chinese Meteorological Administration stations above 2000 m a.s.l. in the eastern and central TP during 1961–2005. Snow depth is positively correlated with the number of snow days (R = 0.89, p < 0.0001). Regional mean winter (DJF) depth and days of snow cover increase at rates of 0.32 mm decade–1 and 0.40 d decade–1 from 1961 to 1990, but at rates of –1.80 mm decade–1 and –1.59 d decade–1 (i.e. decrease) between 1991 and 2005. The long term trends are weakly positive, but unrepresentative of shorter time periods. Thus snow depth and cover change depends on the timescale examined and cannot be attributed solely to increased greenhouse gas forcing. The decreasing snow depth in recent years will influence hydrological processes and water resources on the plateau and downstream. Both snow depth and duration have positive correlations with the winter Arctic Oscillation/North Atlantic Oscillation (AO/NAO) index and Nino-3 region (5°N–5° S, 150°–90° W) sea surface temperature (SST). During high AO/NAO index years, both a deeper India–Burma trough and an intensified cyclonic circulation near Lake Baikal bring more snowfall to the TP, consistent with a higher water vapor flux. The opposite is true in low AO/NAO years. Thus secular changes of snow depth and duration in the TP are not independent of changes in the macro-scale atmospheric circulation.

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

The Tibetan Plateau, with an average elevation of over 4000 m above sea level, is the highest and most extensive highland in the world. Between 1980 and 2005, the annual mean tempera- ture has warmed at the rate of 0.38°C decade -1 . However, little attention has been paid to the variation of wind speed, the most important factor controlling evapotranspiration in the Tibetan Plateau. Here we used monthly mean wind speed from the Chinese Meteorological Administration data set to exa- mine the spatial and temporal variability of wind speed at 71 stations (with elevations above 2000 m above sea level) in the eastern and central Tibetan Plateau during 1980-2005, and compared wind speed climatology and their trends with NCEP and ERA-40 reanalyses in the same domain. Compared with surface stations, NCEP overestimates wind speed and ERA-40 underestimates it, with mean annual biases of 0.93 m s -1 for NCEP and -0.75 m s -1 for ERA-40. Both surface stations and NCEP reanalysis show significant decreasing trends, at rates of -0.24 and -0.13 m s -1 decade -1 , respectively, mainly evident in spring and summer. ERA-40 fails to capture any decrease. The above results indicate that NCEP captures wind speed better than ERA-40. We speculate that the most likely cause of dimin- ishing wind speed are the asymmetrically decreasing latitudinal surface temperature and pressure gradients over the Tibetan Plateau, which may be part of a large-scale atmospheric circulation shift.

Based on the China Meteorological Administration homogenized dataset, the spatial and temporal variations of monthly mean temperature at 71 stations with elevations above 2000 m a.s.l. in the eastern and central Tibetan Plateau (TP) during 1961–2004 are examined. Using principal component analysis (PCA) in S-Mode, four main subregions of temperature variability in the TP are identified. Trend analyses are then carried out on mean series calculated for each subregion and for the eastern and central TP as a whole at annual, seasonal and monthly resolutions. The NE subregion has the most significant warming trends especially in winter and autumn. The PCA method is also applied to sea level pressure (SLP) over the domain of 20°–60°N and 60°–130°E. Different atmospheric circulation patterns are classified in summer and winter. Moreover, temperature series in the TP are often correlated with SLP and associated with different atmospheric circulation patterns. There are more water vapor flux and total cloud cover in the warmer summers and winters. Therefore, we suggest that change in atmospheric circulation is one of the important factors contributing to the recent climate warming of the TP.

Temperature trend magnitudes at 71 homogenized surface stations with elevations above 2000 m asl in the eastern and central Tibetan Plateau (TP) and 56 grid points from surface NCEP and ERA-40 reanalyses in the TP's vicinity are examined. Both the surface meteorological stations and ERA-40 show general warming trends at the majority of locations, especially in winter. NCEP fails to identify this. Compared with the surface stations, both NCEP and ERA-40 reanalysis data underestimate air temperature trends in the TP, but ERA-40 is better than NCEP. There are no simple linear relationships between elevation and temperature trend magnitudes on an annual or seasonal basis in the surface data or ERA-40, and in NCEP this relationship is inconsistent. Instead there are significant correlations between mean annual and seasonal temperatures and temperature trend magnitudes in the surface dataset and NCEP data (but not ERA-40). We suggest this is due to cryospheric feedback since trends are enhanced when mean annual temperatures are near freezing. The absence of any simple elevation dependency in temperature trends suggests that the rapid warming rate derived from high elevation ice-cores in this region should be interpreted with caution. In addition, more attention should be given to the selection of reanalysis to represent surface climate in the TP, since topographical differences between grid points and stations, and other reanalysis model differences such as surface land schemes, cause differences in trend identification and patterns in this critical region.

Based on daily maximum and minimum surface air temperature and precipitation records at 303 meteorological stations in China, the spatial and temporal distributions of indices of climate extremes are analyzed during 1961–2003. Twelve indices of extreme temperature and six of extreme precipitation are studied. Temperature extremes have high correlations with the annual mean temperature, which shows a significant warming of 0.27°C/decade, indicating that changes in temperature extremes reflect the consistent warming. Stations in northeastern, northern, northwestern China have larger trend magnitudes, which are accordance with the more rapid mean warming in these regions. Countrywide, the mean trends for cold days and cold nights have decreased by −0.47 and −2.06 days/decade respectively, and warm days and warm nights have increased by 0.62 and 1.75 days/decade, respectively. Over the same period, the number of frost days shows a statistically significant decreasing trend of −3.37 days/decade. The length of the growing season and the number of summer days exhibit significant increasing trends at rates of 3.04 and 1.18 days/decade, respectively. The diurnal temperature range has decreased by −0.18°C/decade. Both the annual extreme lowest and highest temperatures exhibit significant warming trends, the former warming faster than the latter. For precipitation indices, regional annual total precipitation shows an increasing trend and most other precipitation indices are strongly correlated with annual total precipitation. Average wet day precipitation, maximum 1-day and 5-day precipitation, and heavy precipitation days show increasing trends, but only the last is statistically significant. A decreasing trend is found for consecutive dry days. For all precipitation indices, stations in the Yangtze River basin, southeastern and northwestern China have the largest positive trend magnitudes, while stations in the Yellow River basin and in northern China have the largest negative magnitudes. This is inconsistent with changes of water vapor flux calculated from NCEP/NCAR reanalysis. Large scale atmospheric circulation changes derived from NCEP/NCAR reanalysis grids show that a strengthening anticyclonic circulation, increasing geopotential height and rapid warming over the Eurasian continent have contributed to the changes in climate extremes in China.

The ponding of cold air at low elevations is a major feature of the high-latitude climates of the Arctic, wherever low solar angles combine with incised topography. In Finnish Lapland this cold-air accumulation is critical for flora and fauna (Tenow and Nilssen, 1990; Virtanen et al., 1998) since absolute minimum temperatures control the survival of the eggs of the autumnal moth Epirrita autumnata. This moth is responsible for outbreaks of defoliation of the mountain birch Betula pubescens. Without cold-air accumulation there would be far more destructive outbreaks in the main inhabited areas. Added to the above concern is that of global warming. Warming is expected to be greater than the global average in the high latitudes (IPCC, 2007) and the temperature rise in winter in Finland over the twenty-first century is expected to be particularly large (Jylha et al., 2004). Current predictions made by the Intergovernmental Panel on Climate Change (IPCC) (2007) indicate a best estimate annual warming of around +5 degC for northern Finland by 2099 (~+7 degC in winter), as opposed to +3.2 degC for Europe as a whole (A1B scenario). If the enhancement of greenhouse gases in the atmosphere also alters the propensity for cold-pool formation, local increases in winter temperatures could be even more dramatic than the regional mean, with large consequences for forest damage, local ecology, and the formation/destruction of lake ice in autumn and spring. The cold pool is transient and its formation and destruction are controlled by synoptic conditions (atmospheric gradient winds and cloud cover/radiation balance) as well as the interaction with local topography. The research summarized in this paper comes from a pilot study which aimed to quantify the existence, temporal and spatial extent of the cold pool in Kevo Valley, northern Finland, through operation of an elevationaltransect of automatic temperature loggers.Future research is mapping the spatial extent of this cold pool in more detail, and examining the mechanisms behind its formation and destruction.

A homogenous climate record (1968-2006) is created for Widdybank Fell (515 m) in the Upper Teesdale National Nature Reserve in northern England, one of the longest high-elevation records in the U.K. Separate time series from Widdybank Fell (1968-1995) and nearby Hunt Hall (1996-2006) are combined using a single mobile automatic weather station (AWS) to calibrate between locations based on 5 years of measurements (2000-2005). After instrumental differences are eradicated, transfer functions are developed based on monthly temperature differences, median monthly ratios of wind speed and mean monthly precipitation totals. The resultant monthly time series show limited trends, although minimum temperatures have increased by 0.38°C/decade. There are no secular trends in mean wind speed or monthly precipitation anomalies, in agreement with other studies which suggest northern England is in a transition area between predicted wetting in northern Europe and drying further south.

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...

Previous research has illustrated differences in temperature trends as measured by high elevation surface stations versus free-air temperatures interpolated to the same locations from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research's (NCAR) Re-analysis R1. This paper examines the extent to which the decision to use R1 rather than radiosonde data influenced these results. Temperatures at selected high elevation surface sites (1948–998) are paired with nearby homogeneity adjusted radiosonde data from Lanzante, Klein and Seidel (LKS). For each station pair, four mean monthly temperature anomaly time series are examined, consisting of (1) surface Global Historical Climate Network (GHCNv2)/Climate Research Unit (CRUv2) station anomalies (SF), (2) LKS radiosonde anomalies, and R1 anomalies interpolated to (3) the surface (RNSF) and (4) radiosonde (RNLKS) locations respectively. Analyses demonstrate the extent of common variance, the mean climatology of each of the four series, and differences or similarities in trends. The surface record is decoupled from the other three series especially in locations of incised topography. In 15 out of 18 pairs RNSF shows greater affinity with LKS than with SF and there is a high degree of common variance between LKS and RNSF. There is a high degree of correlation between secular trends in the two R1 series, both of which are much more similar to radiosonde than to surface trends. Trends in raw temperature and in ΔT (the surface/free-air temperature difference) both therefore show limited sensitivity to the choice of LKS radiosonde versus R1 (RNSF), apart from in a few locations in the Eurasian continent. Copyright © 2007 Royal Meteorological Society

There is growing evidence that the rate of warming is amplified with elevation, such that high-mountain environments experience more rapid changes in temperature than environments at lower elevations. Elevation-dependent warming (EDW) can accelerate the rate of change in mountain ecosystems, cryospheric systems, hydrological regimes and biodiversity. Here we review important mechanisms that contribute towards EDW: snow albedo and surface-based feedbacks; water vapour changes and latent heat release; surface water vapour and radiative flux changes; surface heat loss and temperature change; and aerosols. All lead to enhanced warming with elevation (or at a critical elevation), and it is believed that combinations of these mechanisms may account for contrasting regional patterns of EDW. We discuss future needs to increase knowledge of mountain temperature trends and their controlling mechanisms through improved observations, satellite-based remote sensing and model simulations.

This paper outlines the variation in air temperature in the eastern Pyrenees (Pyrenees Orientales), in particular examining the role of topography. As part of a research programme investigating the relationship between the distribution of the Saddle-backed bushcricket (Ephippiger ephippiger) and climate, an extensive temperature database has been created. This allows us to examine the spatial and temporal variation in the temperature field. In particular this case-study illustrates the importance of the interaction between local scale aspect, synoptic conditions and coastal influences in controlling mountain temperatures.

This paper compares high-elevation surface temperatures based on the Global Historical Climate Network/Climatic Research Unit (GHCN/CRU) and snow telemetry (SNOTEL) datasets, with simultaneous free-air equivalent temperatures, interpolated from NCEP–NCAR reanalysis. Mean monthly temperature anomalies from 1982 to 1999 are examined for 60 SNOTEL and 296 GHCN/CRU sites at elevations over 500 m with relatively homogenous records. The surface/free-air temperature difference ΔT (Ts − Ta) is calculated for both the SNOTEL and GHCN/CRU datasets. Topography influences the correlation between surface and free-air temperature anomalies. Physically realistic diurnal and seasonal changes in ΔT\E are illustrated. Systematic secular trends in surface temperatures, free-air temperatures, and ΔT are revealed, but the sign and magnitude of change depends on location, meaning that regional signals are weak. The Ts trends are positive for most GHCN and CRU sites, and for SNOTEL sites at night. Daytime cooling in the SNOTEL network reduces the mean daily warming trend. The Ta trends are consistently positive for both networks and are often larger than Ts. Thus mean ΔT trends are negative for both datasets. The smaller sample size in the SNOTEL dataset means that error estimates for regional signals are much wider than for the GHCN/CRU dataset. Trend difference maps identify potentially anomalous SNOTEL records. Trends show no correlation with elevation and topography. Surface trends show higher variability and account for most of the uncertainty in ΔT trends. Sensitivity of trends to time period is also discussed. Such changes in the free-air/surface temperature difference may indicate change in the energy balance of mountain areas.

A high elevation data set of surface temperatures from the Front Range of the Rocky Mountains in Colorado, USA, is analysed for evidence of long-term change (1952–98). Sites range from the high plains of Colorado (1509 m) to the alpine tundra (3749 m). Systematic changes in surface-based lapse rates are uncovered, with absolute cooling at the highest elevations, but little temperature change on the high plains. There is lapse-rate steepening at the higher elevations (>3000 m). A synoptic analysis using gridded pressure data shows lapse rate changes to be largely independent of synoptic type. Radiosonde ascents from Denver (1956–98) and Grand Junction (1946–98) are used to derive air equivalent temperatures (AETs) at the same elevations as the surface records. AETs show a contrasting temporal trend, with absolute warming at all levels. Furthermore, free-air lapse rates are weakening at higher elevations, the warming becoming stronger with height. A comparison of the two data sets through derivation of free-air–surface temperature differences shows that the alpine tundra zone of the high Rockies is becoming a progressively stronger heat sink. Possible explanations include increased snow cover, enhanced air movement over the surface and decreased solar radiation input. The heat sink enhancement has led to rapid cooling in the alpine tundra that could not be predicted from the free-air record, casting doubt upon the strong dependence on free-air temperature changes in climate modelling when investigating the potential effects of global warming in mountainous regions. In addition, these local surface trends are of the opposite sign to global and other regional trends identified in many recent observational and modelling studies. Copyright © 2002 Royal Meteorological Society.

Most GCMs indicate distinct elevational signals in temperature response to global warming, both in the free-air and at the surface, although modelled changes are spatially variable, in magnitude and in sign. In this study, daily climate observations (1968–1995) from two sites in northern England, representative of upland and lowland environments, are used to derive a regionally representative lapse rate. The lapse rates of daily maximum and minimum temperatures show strong seasonal and diurnal patterns, and relationships with synoptic conditions, classified using the Lamb classification. Synoptic types with westerly components show the most rapid decrease of temperature with elevation. Lapse rates are also steeper when there is a strong altitudinal increase in cloud cover, decrease in sunshine duration, or strong wind shear.

The long-term climate records of the Mountain Research Station (MRS) at the University of Colorado cover a range of elevations from the lower montane forest zone (~2000–2400 m), through the upper m...

The acidity and conductivity of precipitation at two sites located east of the Continental Divide in the Front Range of Colorado is examined for temporal trends, differences, and relationships to atmospheric circulation patterns for a 14 yr period (1984–1997). The elevationally lower station, Sugarloaf, is about 20 km west of Boulder, CO, and closer to the Denver/Boulder urban corridor than the higher site, Niwot, which lies 11.4 km northwest of Sugarloaf, and 1000 m higher in elevation. Key findings of this study are that Sugarloaf precipitation has the higher pH (less acidic) and lower conductivity of the two sites, and that different circulation patterns are associated with different inter-site precipitation characteristics: chemistry, amount, occurrence, and seasonal differences. Circulation indices account for about one-fourth to one-third of the variability in precipitation chemistry, and synoptic scale circulation patterns are clearly different for extremely low versus extremely high pH conditions at these two sites.

The Pennine uplands of northern England have long been studied as a maritime environment extremely sensitive to small climatic fluctuations (Manley 1942, 1943; Pepin 1995, 1997). There is usually a rapid decrease in temperature with elevation associated with the frequently mobile circulation and particularly the instability of the prevailing polar maritime airmass (Harding 1978, 1979). However, in contrast to the usual decline in temperature and strong increase in wind speed, cloud cover and precipitation with elevation, there are occasional spells of more settled weather when in some cases temperatures experienced on the ground may increase with elevation (a temperature inversion). The relative frequency and characteristics of such conditions are examined in this article.

Recent high-resolution meteorological data from the Pennines of northern England are used to study temporal variation in surface temperature lapse rates. A regression approach uncovers significant ...

This paper analyses the geographical variation in changes in lighting conditions at opposite ends of the working day which would arise from the proposal to align UK clocks with those in Europe. Strong spatial contrasts are illustrated, the pattern of benefit and disadvantage depending on the threshold times used to define darkness. In most areas disadvantage outweighs benefit. In addition, comparisons are made with mainland Europe.

The author, on a recent visit to the mountain kingdom of Lesotho, had the opportunity to talk to villagers concerning their knowledge of weather and climate and this article seeks to describe and analyse some of the results obtained. Although the indigenous knowledge is compared with the insight given by meteorological science, this article does not seek to make valued judgements on the validity and usefulness of the indigenous knowledge, but attempts to develop a classification of so-called 'weather lore' using the Lesotho example.

This paper maps the likely changes in growing season strength in Northern England which would be associated with a variety of temperature change scenarios. Estimates of future temperature change, obtained through application of regression analysis and analytical theory, are converted into attendant changes in "thermal potential" (measured by annual accumulated temperatures above 6°C). The scenarios include warm and cold analogues, uni-directional airflow scenarios, arbitrary warming scenarios and two GCM simulations: UKHI (United Kingdom Meteorological Office High Resolution GCM Equilibrium Experiment) and GISS (Goddard Institute for Space Studies). Considerable changes in the thermal potential of Northern England result, especially at high altitudes, and there is great inter-scenario variation. The amount of cultivable land, defined as areas with an annual temperature accumulation of 1000 d°C and above, varies from 74.6% in the control model to over 99% in the two GCM scenarios (2 × CO2). This is to be expected in maritime upland areas such as the Pennines, where growing season strength is extremely sensitive to small changes in mean temperature. Problems in the interpretation of the results are discussed and outlines for future work are given.

[1] We analyzed temperature trends from 460 GHCNv2 weather stations in the western United States for 1948–2006 to determine whether the extent of decoupling of surface temperatures from the free atmosphere influences past change. At each location we derived monthly indices representative of anticyclonicity using NCEP/NCAR 700 hPa reanalysis pressure fields. The number of anticyclonic days minus cyclonic days (A–C) is positively correlated with temperature anomalies at exposed convex sites and in the north of the domain where the free atmosphere controls temperature, anticyclonic months being warmer. In topographic concavities, and in the south of the domain where the influence of upper air ridges and troughs is muted, the relationship is much weaker. We use the gradient of the A–C index–temperature relationship to represent a coupling index, highest at exposed free-air locations. On a mean annual basis there are no strong relationships between temperature trend magnitude, elevation, topographic incision, or coupling index. However, in winter, warming is weaker at decoupled locations, especially when snow cover is present. Where snow is absent in winter, and in fall, the relationship is reversed. Circulation changes (increased cyclonicity) can explain the disparity in warming between decoupled and exposed locations in fall and to a certain extent in winter (increased anticyclonicity), although winter results are also regionally sensitive. Thus, future climate change may be different (amplified or muted dependent on season and/or surface characteristics) in locations prone to surface decoupling, compared with locations exposed to the free atmosphere. Understanding such processes will aid downscaling of future climate change.

[1] In complex terrain, air in contact with the ground becomes cooled from radiative energy loss on a calm clear night and, being denser than the free atmosphere at the same elevation, sinks to valley bottoms. Cold-air pooling (CAP) occurs where this cooled air collects on the landscape. This article focuses on identifying locations on a landscape subject to considerably lower minimum temperatures than the regional average during conditions of clear skies and weak synoptic-scale winds, providing a simple automated method to map locations where cold air is likely to pool. Digital elevation models of regions of complex terrain were used to derive surfaces of local slope, curvature, and percentile elevation relative to surrounding terrain. Each pixel was classified as prone to CAP, not prone to CAP, or exhibiting no signal, based on the criterion that CAP occurs in regions with flat slopes in local depressions or valleys (negative curvature and low percentile). Along-valley changes in the topographic amplification factor (TAF) were then calculated to determine whether the cold air in the valley was likely to drain or pool. Results were checked against distributed temperature measurements in Loch Vale, Rocky Mountain National Park, Colorado; in the Eastern Pyrenees, France; and in Yosemite National Park, Sierra Nevada, California. Using CAP classification to interpolate temperatures across complex terrain resulted in improvements in root-mean-square errors compared to more basic interpolation techniques at most sites within the three areas examined, with average error reductions of up to 3°C at individual sites and about 1°C averaged over all sites in the study areas.

[1] Most climate models suggest amplification of global warming in high mountains, but observations are less clear. Using comprehensive, homogeneity-adjusted temperature records from over 1000 high elevation stations across the globe, we examine the causes of changing temperature trends with elevation, assessing the roles of free atmospheric change, topography (exposure and aspect), and cryospheric feedback. The data show that observed 20th century temperature trends are most rapid near the annual 0°C isotherm due to snow-ice feedback. Mountain summit and freely draining slope sites are dominated by free-air advection and thus have consistent trend magnitudes, with reduced inter-site variance in comparison with incised valley sites where local factors are more important. Thus, while there has been no simplistic elevational increase in warming rates, some generalizations can be made. Water resources and ecosystems near the 0°C isotherm in the extratropics are at increased risk from accelerated warming. The data also suggest that exposed mountain summits, away from the effects of urbanization and topographic sheltering, may provide a relatively unbiased record of the planet's climate.

[1] Trend magnitudes of 11 indices of temperature extremes at 71 stations with elevations above 2000 m a.s.l. in the eastern and central Tibetan Plateau (TP) during 1961–2005 are examined. Most trends in extremes are consistent with general warming in the TP. There are no significant correlations between elevation and trend magnitude of temperature extremes with the exception of TXn (coldest day temperature) and TX10 (cold day frequency). Thus an enhanced sensitivity of temperature extremes at higher elevations in the eastern and central TP is not apparent in the context of recent warming in this region. Although previous work showed a correlation between elevation and mean temperature trends in the TP, this analysis fails to substantiate this relationship for extremes. Analysis of trend magnitudes by topographic type and degree of urbanization show both factors to have a strong influence in this dataset, which overrides that of elevation.

[1] Surface and free-air temperature observations from the period 1948–2002 are compared for 1084 surface locations at high elevations (>500 m) on all continents. Mean monthly surface temperatures are obtained from two homogeneity adjusted data sets: Global Historical Climate Network (GHCN) and Climatic Research Unit (CRU). Free-air temperatures are interpolated both vertically and horizontally from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis R1 2.5° grids at given pressure levels. The compatibility of surface and free-air observations is assessed by examination of the interannual variability of both surface and free-air temperature anomalies and the surface/free-air temperature difference (ΔT). Correlations between monthly surface and free-air anomalies are high. The correlation is influenced by topography, valley bottom sites showing lower values, because of the influence of temporally sporadic boundary layer effects. The annual cycle of the derived surface/free-air temperature difference (ΔT) demonstrates physically realistic variability. Cluster analysis shows coherent ΔT regimes, which are spatially organized. Temporal trends in surface and free-air temperatures and ΔT are examined at each location for 1948–1998. Surface temperatures show stronger, more statistically robust and widespread warming than free-air temperatures. Thus ΔT is increasing significantly at the majority of sites (>70%). A sensitivity analysis of trend magnitudes shows some reliance on the time period used. ΔT trend variability is dominated by surface trend variability because free-air trends are weak, but it is possible that reanalysis trends are unrealistically small. Results are sensitive to topography, with mountaintop sites showing weaker ΔT increases than other sites (although still positive). There is no strong relationship between any trend magnitudes and elevation. Since ΔT change is dependent on location, it is clear that temperatures at mountain sites are changing in ways contrasting to free air.

[1] Contrasts in high-elevation surface and free-tropospheric temperatures between 1971 and 1996 are examined by comparing surface temperatures from a subset of 72 stations in the GHCN (Global Historical Climate Network) and CRU (Climatic Research Unit) homogeneity adjusted surface data sets with free-air temperatures interpolated to the same locations from NCEP/NCAR Reanalysis R1. The selected stations are above the mean elevation of the surrounding topography, often located on mountain summits. Surface temperatures, free-air temperatures, and their difference (ΔT) are found to be related to independent surface cloud observations from the NDP-026C archive, local wind speed, satellite records of snow cover (NSIDC), and reanalysis wind components. Significant correlations are observed at most stations, and correlation spatial patterns are consistent for different subperiods of the record (e.g., presatellite era versus satellite era). Stepwise regression models built to predict surface temperatures, free-air temperatures, and ΔT from the above meteorological parameters typically explain 20–40% of the temperature variability on an annual basis and more for individual seasons. The stationarity of relationships between temperature and snow/cloud/wind is examined by comparing the temporal trends in the original temperatures with predicted trends from the best fit regression model and trends in model residuals. This provides an assessment of how much of any ΔT trends can be accounted for by changes in meteorology. Significant daytime ΔT residual trends occur primarily in Turkey and eastern China, but significant nighttime ΔT residual trends are more geographically widespread. While daytime residual trends may be the result of surface radiative cooling by increasing anthropogenic aerosol, attribution of nighttime residual trends is uncertain.

The Tibetan Plateau (TP), with an average elevation of over 4000 m asl and an area of approximately 2.5 × 10 6 km 2 , is the highest and most extensive highland in the world and has been called the ‘Third Pole’. The TP exerts a huge influence on regional and global climate through thermal and mechanical forcing mechanisms. Because the TP has the largest cryospheric extent outside the polar region and is the source region of all the large rivers in Asia, it is widely recognized to be the driving force for both regional environmental change and amplification of environmental changes on a global scale. Within China it is recognized as the ‘Asian water tower’. In this letter, we summarize the recent changes observed in climate elements and cryospheric indicators on the plateau before discussing current unresolved issues concerning climate change in the TP, including the temporal and spatial components of this change, and the consistency of change as represented by different data sources. Based on meteorological station data, reanalyses and remote sensing, the TP has shown significant warming during the last decades and will continue to warm in the future. While the warming is predominantly caused by increased greenhouse gas emissions, changes in cloud amount, snow-albedo feedback, the Asian brown clouds and land use changes also partly contribute. The cryosphere in the TP is undergoing rapid change, including glacier retreat, inconsistent snow cover change, increasing permafrost temperatures and degradation, and thickening of the active layer. Hydrological processes impacted by glacial retreat have received much attention in recent years. Future attention should be paid to additional perspectives on climate change in the TP, such as the variations of climate extremes, the reliability of reanalyses and more detailed comparisons of reanalyses with surface observations. Spatial issues include the identification of whether an elevational dependency and weekend effect exist, and the identification of spatial contrasts in temperature change, along with their causes. These issues are uncertain because of a lack of reliable data above 5000 m asl.

Different types of land use (LU) have different physical properties which can change local energy balance and hence vertical fluxes of moisture, heat and momentum. This in turn leads to changes in near-surface temperature and moisture fields. Simulating atmospheric flow over complex terrain requires accurate local-scale energy balance and therefore model grid spacing must be sufficient to represent both topography and land-use. In this study we use both the Corine Land Cover (CLC) and United States Geological Survey (USGS) land use databases for use with the Weather Research and Forecasting (WRF) model and evaluate the importance of both land-use classification and horizontal resolution in contributing to successful modelling of surface temperatures and humidities observed from a network of 39 sensors over a 9 day period in summer 2013. We examine case studies of the effects of thermal inertia and soil moisture availability at individual locations. The scale at which the LU classification is observed influences the success of the model in reproducing observed patterns of temperature and moisture. Statistical validation of model output demonstrates model sensitivity to both the choice of LU database used and the horizontal resolution. In general, results show that on average, by a) using CLC instead of USGS and/or b) increasing horizontal resolution, model performance is improved. We also show that the sensitivity to these changes in the model performance shows a daily cycle.