European Centre Hamburg Research Articles

ECHAM5-Simulated Impacts of Two Types of El Niño on the Winter Precipitation Anomalies in South China

AbstractThe authors used an atmospheric general circulation model (AGCM) of European Centre Hamburg Model (ECHAM5.4) and investigated the possible impacts of eastern Pacific (EP) and central Pacific (CP) El Nino on the winter precipitation anomalies in South China. A composite analysis suggested much more rainfall during the mature phase of EP El Nino than in the case of CP El Nino, and their corresponding observed wet centers to be located in the southeast coast and the region to the south of the Yangtze River, respectively. Results obtained on the basis of model-sensitive run imply that the modelsimulated rainfall anomalies agree well with the observation, and the magnitude of simulated rainfall anomalies were found to be reduced when the amplitude of sea surface temperature anomaly (SSTA) forcing of EP and CP El Nino was cut down. These results imply that the rainfall anomaly in South China is very sensitive not only to the type of El Nino but also to its intensity.

Impact of climate change and carbon dioxide fertilization effect on irrigation water demand and yield of soybean in Serbia

SUMMARYThe Decision Support System for Agrotechnology Transfer (DSSAT) v. 4·2 crop model was used to estimate climate change impacts on soybean yield in Serbia in simulations for 2030 and 2050 integration periods using three global climate change models (GCMs): the European Centre Hamburg Model (ECHAM), The Hadley Centre Coupled Model (HadCM) and the National Center for Atmospheric Research Parallel Climate Model (NCAR-PCM) under two scenarios from the IPCC Special Report on Emissions Scenarios (IPCC 2001): A1B SRES and A2 SRES. Input data included weather data from a 1971–2000 baseline period from ten weather stations assimilated from the Republic Hydrometeorological Service of Serbia. Output results from the three GCMs under the two scenarios for 2030 and 2050 were statistically downscaled with the ‘Met & Roll’ weather generator for predicted climate conditions. Mechanical and chemical soil properties were collected in the vicinity of weather stations and analysed by the Agency for Environmental Safety in Belgrade. Genetic coefficients, for the soybean maturity group II variety, were slightly modified using the DSSAT-SOYGRO model ones. The results showed a considerable benefit of carbon dioxide fertilization on soybean yield and yield increases at all locations. The greatest estimated yield increases obtained using outputs the HadCM model for 2030 both scenarios; in 2050, however, the A2 scenario resulted in smaller increase in yield at some locations. The highest increase in yield was in the central and eastern parts of Serbia. Analyses of the climate change impacts on irrigation demand showed a great increase in the irrigation demand amount per growing season. The average irrigation demand reached the highest values in the southern and eastern parts of Serbia. Water productivity reached highest values in eastern and central locations, while the minimum is expected in the most southern and northern location. According to all results it can be concluded that soybean will benefit greatly under climate change conditions and that soybean cropping, currently most concentrated in the Vojvodina region in northern Serbia, expanding in the central part and one location in eastern Serbia.

Major modes of short-term climate variability in the newly developed NUIST Earth System Model (NESM)

Abstract A coupled earth system model (ESM) has been developed at the Nanjing University of Information Science and Technology (NUIST) by using version 5.3 of the European Centre Hamburg Model (ECHAM), version 3.4 of the Nucleus for European Modelling of the Ocean (NEMO), and version 4.1 of the Los Alamos sea ice model (CICE). The model is referred to as NUIST ESM1 (NESM1). Comprehensive and quantitative metrics are used to assess the model’s major modes of climate variability most relevant to subseasonal-to-interannual climate prediction. The model’s assessment is placed in a multi-model framework. The model yields a realistic annual mean and annual cycle of equatorial SST, and a reasonably realistic precipitation climatology, but has difficulty in capturing the spring-fall asymmetry and monsoon precipitation domains. The ENSO mode is reproduced well with respect to its spatial structure, power spectrum, phase locking to the annual cycle, and spatial structures of the central Pacific (CP)-ENSO and eastern Pacific (EP)-ENSO; however, the equatorial SST variability, biennial component of ENSO, and the amplitude of CP-ENSO are overestimated. The model captures realistic intraseasonal variability patterns, the vertical-zonal structures of the first two leading predictable modes of Madden-Julian Oscillation (MJO), and its eastward propagation; but the simulated MJO speed is significantly slower than observed. Compared with the T42 version, the high resolution version (T159) demonstrates improved simulation with respect to the climatology, interannual variance, monsoon-ENSO lead-lag correlation, spatial structures of the leading mode of the Asian-Australian monsoon rainfall variability, and the eastward propagation of the MJO.

Global-scale remote sensing of water isotopologues in the troposphere: representation of first-order isotope effects

Abstract. Over the last decade, global-scale data sets of atmospheric water vapor isotopologues (HDO) have become available from different remote sensing instruments. Due to the observational geometry and the spectral ranges that are used, few satellites sample water isotopologues in the lower troposphere, where the bulk of hydrological processes within the atmosphere take place. Here, we compare three satellite HDO data sets, two from the Tropospheric Emission Spectrometer (TES retrieval version 4 and 5) and one from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), with results from the atmospheric global circulation model ECHAM4 (European Centre HAMburg 4). We examine a list of known isotopologue effects to qualitatively benchmark the various observational data sets. TES version 5 (TESV5), TES version 4 (TESV4), SCIAMACHY, ECHAM, and ECHAM convolved with averaging kernels of TES version 5 (ECHAMAK5) successfully reproduced a number of established isotopologue effects such as the latitude effect, the amount effect, and the continental effect. The improvement of TESV5 over TESV4 is confirmed by the steeper latitudinal gradient at higher latitudes in agreement with SCIAMACHY. Also the representation of other features of the water isotopologue cycle, such as the seasonally varying signal in the tropics due to the movement of the Intertropical Convergence Zone (ITCZ), is improved in TESV5 and SCIAMACHY compared to TESV4. A known humidity bias due to the cross correlation of H2O and HDO measurements, which is of particular importance for instruments with low sensitivity close to the surface, was analyzed by applying either a humidity bias correction or a suitable a posteriori analysis. We suggest that the qualitative and quantitative tests carried out in this study could become benchmark tests for evaluation of future satellite isotopologue data sets.

Trends and projections of temperature, precipitation, and snow cover during snow cover-observed period over southwestern Iran

In the present study, tendencies in temperature, precipitation, and snow cover area over the southwestern part of Iran have been assessed. The research mainly focused on snow cover-observed period which included the months of December, January, February, March, and April in the area. This research has been divided into two parts. First part consists of an analysis of the trends in temperature, precipitation, and snow cover area during the above months. Trends in these parameters were tested by linear regression, and significance was determined by t test. Mann-Kendall rank test (MK test) was also employed to confirm the results of linear regression. Sequential Mann-Kendall test (SQ-MK test) was applied for change point detection in the series. For snow cover analysis, remote sensing images from National Oceanic and Atmospheric Administration (NOAA) satellite with advanced very high resolution radiometer (AVHRR) sensor for the period 1987–2007 were used. The second part of the research involved future projections based on four models under B1 and A1B emission scenarios. The models used were centre national de recherches meteorologiques (CNRM), European Center Hamburg model (ECHAM), Model for Interdisciplinary Research on Climate (MIROCH) and United Kingdom Meteorological Office (UKMOC) under the Intergovernmental Panel on Climate Change (IPCC) AR4. The analysis of temperature trends revealed a significant increase during February and April. Temperature projections showed that temperature may increase between 1.12 to 7.87 °C by 2100 in the study area. The results of precipitation series indicated that majority of the stations registered insignificant trends during the twentieth century. However, precipitation may decrease according to most of the models under both scenarios, but the decrease may not be large, except according to MIROCH model. The results of trend analysis of snow cover area indicated that no significant trends were detected by any statistical tests at 95 % confidence level during the twentieth century. Snow cover projection showed that snow cover area may decrease as indicated by all the models under both scenarios at the end of twenty-first century consistent with the projected increase in temperature.

Model-simulated trend of surface carbon monoxide for the 2001–2010 decade

Abstract. We present decadal trend estimates of surface carbon monoxide (CO) simulated using the atmospheric chemistry general circulation model ECHAM5/MESSy (EMAC; ECHAM5 and MESSy stand for fifth-generation European Centre Hamburg general circulation model and Modular Earth Submodel System, respectively) based on the emission scenarios Representative Concentration Pathways (RCP) 8.5 for anthropogenic activity and Global Fire Emissions Database (GFED) v3.1 for biomass burning from 2001 through 2010. The spatial distribution of the modeled surface CO is evaluated with monthly data from the Measurements Of Pollution In The Troposphere (MOPITT) thermal infrared product. The global means of correlation coefficient and relative bias for the decade 2001–2010 are 0.95 and −4.29%, respectively. We also find a reasonable correlation (R = 0.78) between the trends of EMAC surface CO and full 10-year monthly records from ground-based observation (World Data Centre for Greenhouse Gases, WDCGG). Over western Europe, eastern USA, and northern Australia, the significant decreases in EMAC surface CO are estimated at −35.5 ± 5.8, −59.6 ± 9.1, and −13.7 ± 9.5 ppbv decade−1, respectively. In contrast, the surface CO increases by +8.9 ± 4.8 ppbv decade−1 over southern Asia. A high correlation (R = 0.92) between the changes in EMAC-simulated surface CO and total emission flux shows that the significant regional trends are attributed to the changes in primary and direct emissions from both anthropogenic activity and biomass burning.

Hydrologic landscape classification evaluates streamflow vulnerability to climate change in Oregon, USA

Abstract. Classification can allow for evaluations of the hydrologic functions of landscapes and their responses to stressors. Here we demonstrate the use of a hydrologic landscape (HL) approach to evaluate vulnerability to potential future climate change at statewide and basin scales in the state of Oregon. The HL classification has five components: climate, seasonality, aquifer permeability, terrain, and soil permeability. We evaluate changes when the 1971–2000 HL climate indices are recalculated using 2041–2070 simulation results from the ECHAM (European Centre HAMburg) and PCM (Parallel Climate Model) climate models with the A2, A1b, and B1 emission scenarios. Changes in climate class were modest (4–18%) statewide. However, there were major changes in seasonality class for five of the six realizations (excluding PCM_B1): Oregon shifts from being 13% snow-dominated to 4–6% snow-dominated under these five realizations, representing a 56–68% reduction in snowmelt-dominated area. At the basin scale, simulated changes for the Siletz Basin, in Oregon's Coast Range, include a small switch from very wet to wet climate, with no change in seasonality. However, there is a modest increase in fall and winter water due to increased precipitation. For the Sandy Basin, on the western slope of the Cascades, HL climate class does not change, but there are major changes in seasonality, especially for areas with low aquifer permeability, which experiences a 100% loss of spring seasonality. This would reduce summer baseflow, but effects could potentially be mitigated by streamflow buffering effects provided by groundwater in the high aquifer permeability portions of the upper Sandy. The Middle Fork John Day Basin (MFJD), in northeastern Oregon, is snowmelt-dominated. The basin experiences a net loss of wet and moist climate area, along with an increase in dry climate area. The MFJD also experiences major shifts from spring to winter seasonality, representing a 20–60% reduction in snowmelt-dominated area. Altered seasonality and/or magnitude of seasonal streamflows could potentially affect survival, growth and reproduction of salmonids in these watersheds, with the greatest effects projected for the MFJD. A major strength of the HL approach is that results can be applied to similarly classified, ungaged basins. Information resulting from such evaluations can help inform management responses to climate change at regional and basin scales without requiring detailed modeling efforts.

Precipitation analysis over southwest Iran: trends and projections

Analysis of trends and projection of precipitation are of significance for the future development and management of water resource in southwest Iran. This research has been divided into two parts. The first part consists of an analysis of the precipitation over 50 stations in the study region for the period 1950–2007. The trends in this parameter were detected by linear regression and significance was tested by t test. Mann–Kendall rank test was also employed to confirm the results. The second part of the research involved future projection of precipitation based on four models. The models used were Centre National de Recherches Meteorologiques (CNRM), European Center Hamburg Model (ECHAM), Model for Interdisciplinary Research on Climate (MIROCH) and United Kingdom Meteorological Office (UKMOC). Precipitation projections were done under B1 and A1B emissions scenarios. The results of precipitation series indicated that most stations showed insignificant trend in annual and seasonal series. The highest numbers of stations with significant trends occurred in winter while no significant trends were detected by statistical tests in summer precipitation. No decreasing significant trends were detected by statistical tests in annual and seasonal precipitation series. The result of projections showed that precipitation may decrease according to majority of the models under both scenarios but the decrease may not be large, except according to MIROCH model. Autumn precipitation may increase with higher rates than other seasons at the end of this century.

Atmospheric Circulation Changes in Response to an Observed Stratospheric Zonal Ozone Anomaly

In a sensitivity study, the influence of an observed stratospheric zonal ozone anomaly on the atmospheric circulation was investigated using the Fifth Generation European Centre Hamburg Model (ECHAM5) which is a general circulation model. The model was run from 1960 to 1999 (40 years) with a mean seasonal cycle of zonally symmetric ozone. In order to isolate the induced dynamical influence of the observed zonally asymmetric part of the three-dimensional stratospheric ozone, a second run was performed for the boreal extratropics using prescribed monthly means from the 40-year reanalysis dataset from the European Centre for Medium-range Weather Forecasts (ERA-40). The main findings are the interdecadal westward shift of the polar vortex at about 65°N and a significant increase in the number of stratospheric sudden warmings during the 1980–99 period. Under the action of zonally asymmetric ozone a decrease in the Arctic Oscillation was identified between the mid-1980s and the mid-1990s. The lag correlation between the mean Arctic Oscillation at the surface and the daily stratospheric northern annular mode increased in mid-winter. Furthermore, we examined the influence of the stratospheric zonal ozone anomaly on Rossby wave breaking in the upper troposphere and found a significant westward shift of poleward Rossby wave breaking events over western Europe in the winter. By this we show that the stratospheric zonal ozone anomaly has a strong influence on the tropospheric circulation as a result of enhanced dynamical coupling processes.

Serial clustering of extratropical cyclones over the North Atlantic and Europe under recent and future climate conditions

Under particular large‐scale atmospheric conditions, several windstorms may affect Europe within a short time period. The occurrence of such cyclone families leads to large socioeconomic impacts and cumulative losses. The serial clustering of windstorms is analyzed for the North Atlantic/western Europe. Clustering is quantified as the dispersion (ratio variance/mean) of cyclone passages over a certain area. Dispersion statistics are derived for three reanalysis data sets and a 20‐run European Centre Hamburg Version 5 /Max Planck Institute Version–Ocean Model Version 1 global climate model (ECHAM5/MPI‐OM1 GCM) ensemble. The dependence of the seriality on cyclone intensity is analyzed. Confirming previous studies, serial clustering is identified in reanalysis data sets primarily on both flanks and downstream regions of the North Atlantic storm track. This pattern is a robust feature in the reanalysis data sets. For the whole area, extreme cyclones cluster more than nonextreme cyclones. The ECHAM5/MPI‐OM1 GCM is generally able to reproduce the spatial patterns of clustering under recent climate conditions, but some biases are identified. Under future climate conditions (A1B scenario), the GCM ensemble indicates that serial clustering may decrease over the North Atlantic storm track area and parts of western Europe. This decrease is associated with an extension of the polar jet toward Europe, which implies a tendency to a more regular occurrence of cyclones over parts of the North Atlantic Basin poleward of 50°N and western Europe. An increase of clustering of cyclones is projected south of Newfoundland. The detected shifts imply a change in the risk of occurrence of cumulative events over Europe under future climate conditions.

Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise

We assess the effect of enhanced basal sliding on the flow and mass budget of the Greenland ice sheet, using a newly developed parameterization of the relation between meltwater runoff and ice flow. A wide range of observations suggest that water generated by melt at the surface of the ice sheet reaches its bed by both fracture and drainage through moulins. Once at the bed, this water is likely to affect lubrication, although current observations are insufficient to determine whether changes in subglacial hydraulics will limit the potential for the speedup of flow. An uncertainty analysis based on our best-fit parameterization admits both possibilities: continuously increasing or bounded lubrication. We apply the parameterization to four higher-order ice-sheet models in a series of experiments forced by changes in both lubrication and surface mass budget and determine the additional mass loss brought about by lubrication in comparison with experiments forced only by changes in surface mass balance. We use forcing from a regional climate model, itself forced by output from the European Centre Hamburg Model (ECHAM5) global climate model run under scenario A1B. Although changes in lubrication generate widespread effects on the flow and form of the ice sheet, they do not affect substantial net mass loss; increase in the ice sheet's contribution to sea-level rise from basal lubrication is projected by all models to be no more than 5% of the contribution from surface mass budget forcing alone.

The Changing Length of the Warming Period of the Annual Temperature Cycle in the High Latitudes Under Global Warming

The mechanism of climate change involves not only an increase in surface temperature but also an adjustment of the global seasons through changes in the timing of the annual temperature cycle. By locating the temperature extrema in monthly temperature records using Lagrangian interpolation in regions where a single maximum and minimum occurs, we define the warming period as the interval between the dates of the temperature minimum and the temperature maximum. The length and mid-point of the warming period are objective measures which can be computed from reanalysis data and from climate model predictions. We have used the 40-year reanalysis dataset from the European Centre for Medium-range Weather Forecasts (ERA40) and the European Centre Hamburg Model (ECHAM5) simulations to investigate the global distribution of the length and mid-point of the warming period for the present climate (1958–2001) and under global warming (Intergovernmental Panel on Climate Change, Fourth Assessment Report, Special Report on Emissions Scenarios; IPCC AR4 SRES A1B scenario) for the period 2157–2200. The results show that the warming period is remarkably uniform in the extratropical temperate latitudes, where it is about 22 days shorter than the cooling period in the ocean and of similar length on land. In the polar region, sharp geographical differences in the length and mid-point of the warming period occur over the ocean and over land which we attribute to the presence of sea ice. Under global warming, these differences are eroded and the temperate regime is extended poleward by about 10° in both hemispheres. This regime change is of particular importance to Canada, on which the discussion on global warming in high latitudes is focused. RÉSUMÉ [Traduit par la rédaction] Le mécanisme du changement climatique implique non seulement une augmentation de la température de surface mais aussi un ajustement des saisons dans leur ensemble par suite de changements dans le cycle annuel des températures. En repérant les extrêmes de température dans les registres météorologiques mensuels au moyen de l'interpolation lagrangienne dans les régions où se produisent un maximum et un minimum uniques, nous définissons la période de réchauffement comme l'intervalle entre la date du minimum et celle du maximum de température. La durée et le point médian de la période de réchauffement sont des mesures objectives pouvant être établies à partir de données de réanalyse et de prévisions de modèle climatique. Nous avons utilisé l'ensemble de données de réanalyse de 40 ans (ERA40) du Centre européen pour les prévisions météorologiques à moyen terme et les simulations du modèle de Hambourg (ECHAM5) du Centre européen pour étudier la distribution planétaire de la durée et du point médian de la période de réchauffement pour le climat présent (1958–2001) et suite au réchauffement planétaire (Groupe d'experts intergouvernemental sur l'évolution du climat, Quatrième Rapport d’évaluation, Rapport spécial sur les scénarios d’émissions; scénario IPCC AR4 SRES A1B) pour la période 2157–2200. Les résultats montrent que la période de réchauffement est remarquablement uniforme dans les latitudes de température extratropicale, où elle est d'environ 22 jours plus courte que la période de refroidissement sur l'océan et d'une durée similaire sur la terre. Dans la région polaire, des différences géographiques marquées sur la durée et le point médian de la période de réchauffement se produisent dans l'océan et sur la terre, différences que l'on attribue à la présence de glace de mer. Avec le réchauffement planétaire, ces différences s'érodent et le régime tempéré s'étend vers le pôle par environ 10° dans les deux hémisphères. Ce changement de régime est particulièrement important pour le Canada, auquel se rapporte la discussion sur le réchauffement planétaire dans les hautes latitudes.

Temperature analysis over southwest Iran: trends and projections

The present study intends to show the effect of climate change on trends and patterns of temperature over the southwestern part of Iran. The research has been divided into two parts. The first part consists of an analysis of the temperature trends of mean temperature (TM), maximum temperature (TMAX), and minimum temperature (TMIN) over 39 stations in the study region for the period 1950–2007. The trends in these parameters were detected by linear regression, and significance was tested by t test. Mann–Kendall rank test (MK test) was also employed to confirm the results. The second part of the research involved future projection of temperature based on four models. The models used were Centre National de Recherches Meteorologiques, European Center Hamburg Model, Model for Interdisciplinary Research on Climate, and UK Meteorological Office. Temperature projections were done under B1 and A1B emissions scenarios. The analysis of temperature trends revealed a significant increase during summer and spring seasons. TMAX was stable than TMIN and TM, and winter was stable as compared with summer, spring, and autumn seasons. Results of modeling showed that temperature may increase between 1.69 and 6.88 °C by 2100 in the study area. Summer temperatures may increase with higher rates than spring, winter, and autumn temperatures.

A global climatology of upper-tropospheric ice supersaturation occurrence inferred from the Atmospheric Infrared Sounder calibrated by MOZAIC

Abstract. Ice supersaturation in the upper troposphere is a complex and important issue for the understanding of cirrus cloud formation. On one hand, infrared sounders have the ability to provide cloud properties and atmospheric profiles of temperature and humidity. On the other hand, they suffer from coarse vertical resolution, especially in the upper troposphere and therefore are unable to detect shallow ice supersaturated layers. We have used data from the Measurements of OZone and water vapour by AIrbus in-service airCraft experiment (MOZAIC) in combination with Atmospheric InfraRed Sounder (AIRS) relative humidity measurements and cloud properties to develop a calibration method for an estimation of occurrence frequencies of ice supersaturation. This method first determines the occurrence probability of ice supersaturation, detected by MOZAIC, as a function of the relative humidity determined by AIRS. The occurrence probability function is then applied to AIRS data, independently of the MOZAIC data, to provide a global climatology of upper-tropospheric ice supersaturation occurrence. Our climatology is then compared to ice supersaturation occurrence statistics from MOZAIC alone and related to high cloud occurrence from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). As an example of application it is compared to model climatologies of ice supersaturation from the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) and from the European Centre HAmburg Model (ECHAM4). This study highlights the benefits of multi-instrumental synergies for the investigation of upper tropospheric ice supersaturation.

Influence of Tropical Indian Ocean Warming and ENSO on Tropical Cyclone Activity over the Western North Pacific

In this study, we have investigated contributions of tropical Indian Ocean (IO) sea surface temperature (SST) warming and El Nino—Southern Oscillation (ENSO) to the interannual variability of tropical cyclone (TC) genesis frequency over the western North Pacific (WNP) between 1948 and 2010 and the involved physical mechanisms. Both ENSO and tropical IO Basin Mode (IOBM) warming are found to play important roles in modulating the WNP TC genesis frequency, but their effects are significantly different. The time series of seasonal empirical orthogonal function of tropical IO and tropical Pacific SST with trend and multi-decadal variability removed are defined as the IOBM index and ENSO index, respectively. The results show that the IO warming year is usually the El Nino decaying year. The number of total TCs, especially weak TCs, decreases during the tropical IO warming year when an anomalous anticyclonic circulation is observed over the tropical Northwest Pacific off the equator. On the other hand, the number of intense TCs increases in the El Nino developing year because of the eastward shifts of both the western Pacific monsoon trough and the cyclonic shear of the equatorial westerlies, and thus the eastward shift of the main TC genesis region. It is also found that the relationship between ENSO and the frequency of intense TCs has a decadal variation. During 1968–1987, the number of intense TCs was not related to ENSO with a correlation coefficient of only 0.19, while the correlation coefficient is 0.63 and 0.73 during 1948–1967 and 1988–2007, respectively. The extent to which the WNP anomalous anticyclone is forced by IO warming is investigated by using the global climate model (European Centre Hamburg Model, ECHAM) with imposed SST anomalies over the tropical IO. The results suggest that the WNP anomalous anticyclone that develops from June to September results mainly from the northward shift of the tropical IO warming from boreal spring to boreal summer.

Effects of ice nuclei on cirrus clouds in a global climate model

[1] A multiple-mode ice microphysical scheme is applied in the European Centre/Hamburg (ECHAM) general circulation model to simulate effects of aerosol-ice interactions on global cirrus properties. The different ice modes represent cirrus ice formed by homogeneous freezing of liquid aerosols and heterogeneous nucleation on mineral dust or black carbon particles. A fourth ice mode represents ice from other sources. The competition of these modes for available water is realized in a physical parameterization scheme considering also the effect of preexisting ice on the ice nucleation process. The model is applied to analyze the global characteristics of ice formed by the different aerosol types and to study potential global effects of mineral dust and black carbon particles on cirrus microphysical parameters. The simulations reveal that, on average, ice from heterogeneous nucleation shows fewer but larger crystals and has a smaller contribution to the mean cirrus ice water content than ice from homogeneous freezing. However, heterogeneous ice nuclei may have important effects on the overall cirrus properties. Reductions in zonal mean annual average cirrus ice particle number concentrations induced by heterogeneous nucleation of up to 20% in the tropics and 1%–10% in the midlatitudes are simulated. The effect is further amplified by ice formation on aircraft-generated soot. Significant reductions in the mean ice water content are modeled, which likely result from efficient sedimentation and precipitation of large ice particles generated by heterogeneous nucleation. This leads to reductions in the zonal mean annual average water vapor mixing ratio of up to 5% at cirrus levels.

Simulating climate change and its effects on the wind energy resource of Ireland

ABSTRACTWe consider the impact of climate change on the wind energy resource of Ireland using an ensemble of Regional Climate Model (RCM) simulations. The RCM dynamically downscales the coarse information provided by the Global Climate Models (GCMs) and provides high resolution information, on a subdomain covering Ireland. The RCM used in this work is the Rossby Center's RCM (RCA3).The RCA3 model is evaluated by performing simulations of the past Irish climate, driven by European Center for Medium‐Range Weather Forecasts ERA‐40 data, and by comparing the output to observations. Results confirm that the output of the RCA3 model exhibits reasonable and realistic features as documented in the historical wind data record. For the investigation of the influence of the future climate under different climate scenarios, the Max Plank Institute's GCM, European Center Hamburg Model, is used to drive the RCA3 model. Simulations are run for a control period 1961‐2000 and future period 2021‐2060. The future climate was simulated using the four Intergovernmental Panel on Climate Change emission scenarios A1B, A2, B1 and B2. The results for the downscaled simulations show a substantial overall increase in the energy content of the wind for the future winter months and a decrease during the summer months. The projected changes for summer and winter were found to be statistically significant over most of Ireland. However, the projected changes should be viewed with caution since the climate change signal is of similar magnitude to the variability of the evaluation and control simulations. Copyright © 2011 John Wiley & Sons, Ltd.

The Sensitivity of Northern Groundwater Recharge to Climate Change: A Case Study in Northwest Alaska1

Clilverd, Hannah M., Daniel M. White, Amy C. Tidwell, and Michael A. Rawlins, 2011. The Sensitivity of Northern Groundwater Recharge to Climate Change: A Case Study in Northwest Alaska. Journal of the American Water Resources Association (JAWRA) 47(6):1228–1240. DOI: 10.1111/j.1752-1688.2011.00569.x Abstract: The potential impacts of climate change on northern groundwater supplies were examined at a fractured-marble mountain aquifer near Nome, Alaska. Well water surface elevations (WSE) were monitored from 2004-2009 and analyzed with local meteorological data. Future aquifer response was simulated with the Pan-Arctic Water Balance Model (PWBM) using forcings (air temperature and precipitation) derived from fifth-generation European Centre Hamburg Model (ECHAM5) global circulation model climate scenarios for extreme and modest increases in greenhouse gases. We observed changes in WSE due to the onset of spring snowmelt, low intensity and high intensity rainfall events, and aquifer head recession during the winter freeze period. Observed WSE and snow depth compared well with PWBM-simulated groundwater recharge and snow storage. Using ECHAM5-simulated increases in mean annual temperature of 4-8°C by 2099, the PWBM predicted that by 2099 later freeze-up and earlier snowmelt will decrease seasonal snow cover by one to two months. Annual evapotranspiration and precipitation are predicted to increase 27-40% (55-81 mm) and 33-42% (81-102 mm), respectively, with the proportion of snowfall in annual precipitation decreasing on average 9-25% (p < 0.05). The amount of snowmelt is not predicted to change significantly by 2099; however, a decreasing trend is evident from 2060 in the extreme ECHAM5 greenhouse gas scenario. Increases in effective precipitation were predicted to be great enough to sustain sufficient groundwater recharge.

Temperature, Relative Humidity, and Divergence Response to High Rainfall Events in the Tropics: Observations and Models

AbstractRadiosonde measurements and Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall are used to construct composite anomaly patterns of temperature, relative humidity, and divergence about high rainfall events in the western Pacific. The observed anomaly patterns are compared with anomaly patterns from four general circulation models [Third and Fourth Generation Atmospheric General Circulation Model (AGCM3 and AGCM4), Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (GFDL CM2.1), and European Center Hamburg Model version 5 (ECHAM5)] and two reanalysis products [40-yr ECMWF Re-Analysis (ERA-40) and ERA-Interim]. In general, the models and reanalyses do not fully represent the timing, strength, or altitude of the midlevel congestus divergence that precedes peak rainfall or the midlevel stratiform convergence that occurs after peak rainfall. The surface cold pools that develop in response to high rainfall events are also either not present or somewhat weaker than observations. Surface cold pools originate from the downward transport within mesoscale downdrafts of midtropospheric air with low moist static energy into the boundary layer. Differences between the modeled and observed response to high rainfall events suggest that the convective parameterizations used by the models and reanalyses discussed here may underrepresent the strength of the mesoscale downdraft circulation.

Forcing mechanism of the seasonally asymmetric quasi‐biennial oscillation secondary circulation in ERA‐40 and MAECHAM5

The seasonality of the quasi‐biennial oscillation (QBO) and its secondary circulation is analyzed in the European Reanalysis (ERA‐40) and Middle Atmosphere European Centre Hamburg Model (MAECHAM5) general circulation model data sets through the multitaper method‐singular value decomposition (MTM‐SVD). In agreement with previous studies, the results reveal a strong seasonal dependence of the QBO secondary circulation. This is characterized by a two‐cell structure symmetric about the equator during autumn and spring. However, anomalies strongly weaken in the summer hemisphere and strengthen in the winter hemisphere, leading to an asymmetric QBO secondary circulation characterized by a single‐cell structure displaced into the winter hemisphere during the solstices. In ERA‐40, this asymmetry is more pronounced during the northern than during the southern winter. These results provide the first observation of the QBO secondary circulation asymmetries in the ERA‐40 reanalysis data set across the full stratosphere and the lower mesosphere, up to 0.1 hPa. The MTM‐SVD reconstruction of the seasonal QBO signals in the residual circulation and the QBO signals in Eliassen Palm (EP) flux divergences suggest a particular mechanism for the seasonal asymmetries of the QBO secondary circulation and its extension across the midlatitudes. The analysis shows that the QBO modulates the EP flux in the winter hemispheric surf zone poleward of the QBO jets. The zonal wind forcing by EP flux divergence is transformed by the Coriolis effect into a meridional wind signal. The seasonality in the stratospheric EP flux and the hemispheric differences in planetary wave forcing cause the observed seasonality in the QBO secondary circulation and its hemispheric differences.