The Bise—Climatology of a regional wind north of the Alps

Summary The Bise is one of several regional winds in the Alpine area occuring in connection with postfrontal pressure rise and cold air advection. Like the Mistral, the Bise is also induced by a synoptiscale 850hPa pressure gradient (dp/dn _(NESW)1 hPa/100 km) and strongly determined by orographic effects.Apart from the classical postfrontal Bise in Spring, a deep Bise with strong cold air advection and sometimes rain appears during winter. A rough survey of the factors determining the wind profile during Bise, which is quite often characterized by a low-level jet structure, shows that dynamical effects induced by the topography like flow splitting, channeling and the formation of countercurrents may be very important.With 11 Figures     

Trends of seasonal maximum and minimum temperatures and precipitation in Southern Brazil for the 1913–2006 period

Long-term variations of monthly average maximum and minimum temperature (TMAX and TMIN) and precipitation records in southern Brazil are investigated for the 1913–2006 period. These variations are carefully analyzed for seasonal and annual indices, taken as regional averages. For this purpose, the serial correlation and trend of the indices are investigated using the run and Mann–Kendall tests. The significant trends are obtained from linear least-square fits. The annual and seasonal TMIN indices show significant warming trends with magnitudes (1.7°C per 100 years for annual index) comparable to those reported by the Intergovernmental Panel on Climate Change, but lower than those found for the southern Brazil in another previous work. Regarding the two other variables, the indices show significant trends only for summer, being a cooling trend of 0.6°C per 100 years for the TMAX and an increasing trend of 93 mm per 100 years over an average summer precipitation of 367 mm. Concerning the decadal analysis, the 1920s present the lowest annual, autumn, and spring TMIN and the 1990s, the highest ones. The 1970s is the decade with the lowest summer TMAX, and the 1940s the decade with the highest one. The driest decade is the 1940s and the wettest, the 1980s.     

Probabilistic model of maximum precipitation depths for Kraków (southern Poland, 1886-2002)

This study was designed to empirically determine what relationships existed between three characteristics of precipitation: maximum depth, duration, and probability of exceedance. Annual maximum series for intervals of between one and 120 h were identified using the 1886-2002 pluviographic record from Kraków. The Gumbel distribution was selected from a group of four of the most popular theoretical maximum value distributions and identified as the optimum solution. Its parameters were determined. Confidence intervals for quantiles were obtained using the bootstrap method. Formulae were derived for the relationships between the Gumbel distribution parameters, i.e., the α location and β scale, depending on precipitation duration. These take the form of a polynomial of the second degree. The model developed was subjected to a two-step validation with a positive result.     

Daily precipitation grids for Austria since 1961—development and evaluation of a spatial dataset for hydroclimatic monitoring and modelling

Theoretical and Applied Climatology - Spatial precipitation datasets that are long-term consistent, highly resolved and extend over several decades are an increasingly popular basis for modelling...     

Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region—and its quantification

Over the tropical oceans, higher sea surface temperatures (SST, above 26 °C) in summer are generally accompanied by increased precipitation. However, it has been argued for the last three decades that, any monotonic increase in precipitation with respect to SST is limited to an upper threshold of 28–29.5 °C, and beyond this, the relationship fails. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific) are mostly above the threshold, SST does not play an active role on the summer monsoon variability. It also implies that increasing SSTs due to a changing climate need not result in increasing monsoon precipitation. The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the results here show that enhanced convection occurs even up to the SST maxima of 31 °C averaged over these basins, challenging any claim of an upper threshold for the SST-convection variability. The study provides us with a novel method to quantify the SST-precipitation relationship. The rate of increase is similar across the basins, with precipitation increasing at ~2 mm day^?1 for an increase of 1 °C in SST. This means that even the high SSTs over the monsoon basins do play an active role on the monsoon variability, challenging previous assumptions. Since the response of precipitation to SST variability is visible in a few days, it would also imply that including realistic ocean–atmosphere coupling is crucial even for short term monsoon weather forecasts. Though recent studies suggest a weakening of the monsoon circulation over the last few decades, results here suggest an increased precipitation over the tropical monsoon regions, in a global warming environment with increased SSTs. Thus the signature of SST is found to be significant for the Asian summer monsoon, in a quantifiable manner, seamlessly through all the timescales—from short-term intraseasonal to long-term climate scales.     

Influence of traffic emissions on the composition of atmospheric particles of different sizes—Part 2: SEM–EDS characterization

In urban areas traffic is the major contributor to atmospheric particulate matter and exposure to these particles currently represents a serious risk to human health. The attention has been recently focused more on the particles of smaller sizes (PM_2.5) which penetrate deeper in respiratory system causing severe health effects. Therefore, more information on PM_2.5 should be provided, namely concerning morphological and chemical characterization. Aiming further evaluation of the impact of traffic emissions on public health, this work evaluated the influence of traffic on the chemical and morphological characteristics of PM₁₀ and PM_2.5, collected at one site influenced by traffic emissions and at one reference site. Chemical and morphological characteristics of 1,000 individual particles were determined by scanning electron microscopy combined with energy dispersive spectrometer (SEM–EDS). Cluster analysis (CA) was used to identify different types of particles that occurred in PM, aiming the identification of the respective emission sources. Traffic PM_2.5 were dominated by particles composed of Fe oxides and alloys (67%) which were related to traffic emissions (this percentage was 3.7 times higher than at the background site); in PM_2.5–10 the abundance of Fe oxides and alloys were 20% and 0% for the traffic and background sites, respectively. Background PM_2.5 were mainly constituted by aluminum silicates (63%) related to natural sources (this percentage was 2.5 times higher than at the traffic site); the abundances of aluminum silicates in PM_2.5–10 were 74% and 73% for traffic and background sites, respectively. It was concluded that traffic emissions were mainly present in PM_2.5 (the percentage of particles associated to these emissions was 3.4 times higher than in PM_2.5–10), while coarse particles were dominated by material of natural origin (the percentage of particles associated was 1.2 and 3.0 times higher than in PM_2.5 for traffic and background sites, respectively). Previous results obtained by proton induced X-ray emission (PIXE) were consistent with SEM–EDS analysis that showed to be very useful to complement elemental analysis of different PM_2.5 and PM_2.5–10.     

Parameterization of Sheared Entrainment in a Well-developed CBL.Part Ⅱ:A Simple Model for Predicting the Growth Rate of the CBL

Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model for predicting the growth rate of a well-developed and sheared CBL. The relative stratification, defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone, is found to be a function of entrainment flux ratio (A _e). This leads to a simple expression of the entrainment rate, in which A _e needs to be parameterized. According to the results in Liu et al. (2016), A _e can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL. The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations. Results indicate that the entrainment process is influenced by the dynamic effect, the interaction between mean shear and environmental stratification, and one other term that includes the Coriolis effect. These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL. This model is validated by outputs of LESs, and the results show that it performs satisfactorily. Compared with bulk models, this model does not need to solve a set of equations for the CBL. It is more convenient to apply in numerical models.     

Climatological assessment of desert targets over East Asia — Australian region for the solar channel calibration of geostationary satellites

Desert targets for solar channel calibration of geostationary satellites in the East Asia — Australian region were selected and their qualities were assessed with aid of Moderate Resolution Imaging Spectroradiometer data (i.e., white-sky surface albedo, aerosol optical thickness, and cloud fraction) from 2002 to 2008. The magnitude, spatial uniformity, and temporal stability of the white-sky surface albedo are examined in order to select bright and stable targets. Subsequently those selected targets over China, India, and Australia are further checked for their qualities in terms of data yielding ratio, aerosol optical thickness, cloud fraction, satellite viewing angle, and solar zenith angle. Results indicate that Chinese targets are found to be not adequate as calibration targets in spite of excellent surface conditions because of high percentage of cloud, possibly heavy aerosol loading, and lower solar elevation angle in particular during winter time. Indian site should be take care about relatively high temporal variation of surface condition and heavy aerosol loading. On the other hand, Australian desert targets are considered to be best when surface brightness, spatial and temporal stability, data yielding ratio, aerosol, and cloud are counted.     

High resolution regional climate model simulations for Germany: Part II—projected climate changes

The projected climate change signals of a five-member high resolution ensemble, based on two global climate models (GCMs: ECHAM5 and CCCma3) and two regional climate models (RCMs: CLM and WRF) are analysed in this paper (Part II of a two part paper). In Part I the performance of the models for the control period are presented. The RCMs use a two nest procedure over Europe and Germany with a final spatial resolution of 7 km to downscale the GCM simulations for the present (1971–2000) and future A1B scenario (2021–2050) time periods. The ensemble was extended by earlier simulations with the RCM REMO (driven by ECHAM5, two realisations) at a slightly coarser resolution. The climate change signals are evaluated and tested for significance for mean values and the seasonal cycles of temperature and precipitation, as well as for the intensity distribution of precipitation and the numbers of dry days and dry periods. All GCMs project a significant warming over Europe on seasonal and annual scales and the projected warming of the GCMs is retained in both nests of the RCMs, however, with added small variations. The mean warming over Germany of all ensemble members for the fine nest is in the range of 0.8 and 1.3 K with an average of 1.1 K. For mean annual precipitation the climate change signal varies in the range of ?2 to 9 % over Germany within the ensemble. Changes in the number of wet days are projected in the range of ±4 % on the annual scale for the future time period. For the probability distribution of precipitation intensity, a decrease of lower intensities and an increase of moderate and higher intensities is projected by most ensemble members. For the mean values, the results indicate that the projected temperature change signal is caused mainly by the GCM and its initial condition (realisation), with little impact from the RCM. For precipitation, in addition, the RCM affects the climate change signal significantly.     

Analysis of the climatic constraints to maize production in the current agricultural region of Argentina—a probabilistic approach

A simple method of analysis was proposed to characterize the impact of climatic conditions of a wide region of Argentina (from 27°05′S to 35°48′S, from 61°5′W to 64°21′W) on potential maize (Zea mays L.) grain yield, and the occurrence of various climatic constraints (low temperatures and low soil water content, frost, drought stress and heat stress) along the cycle. The analysis was based on previous studies of the eco-physiology of maize crops and the use of climatic records of six locations in the region under study. Results were analyzed using a probabilistic method, later organized as a checklist to consider when deciding on sowing date in a location of the region. Thus, for each production scenario (combination of location and sowing date), farmers would have a tool enabling them to pay particular attention to the restrictions more likely to occur, to include some cultural practices to avoid or mitigate the most severe climatic constraint to maize production.     

An Updated Coupled Model for Land-Atmosphere Interaction. Part Ⅰ: Simulations of Physical Processes

A new two-way land-atmosphere interaction model (R42_AVIM) is fulfilled by coupling the spectral at- mospheric model (SAMIL_R42L9) developed at the State Key Laboratory of Numerical Modeling for Atmo- spheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sci- ences (LASG/IAP/CAS) with the land surface model, Atmosphere-Vegetation-Interaction-Model (AVIM). In this coupled model, physical and biological components of AVIM are both included. Climate base state and land surface physical fluxes simulated by R42_AVIM are analyzed and compared with the results of R42_SSIB [which is coupled by SAMIL_R42L9 and Simplified Simple Biosphere (SSIB) models]. The results show the performance of the new model is closer to the observations. It can basically guarantee that the land surface energy budget is balanced, and can simulate June-July-August (JJA) and December-January- February (DJF) land surface air temperature, sensible heat flux, latent heat flux, precipitation, sea level pressure and other variables reasonably well. Compared with R42_SSIB, there are obvious improvements in the JJA simulations of surface air temperature and surface fluxes. Thus, this land-atmosphere coupled model will offer a good experiment platform for land-atmosphere interaction research.     

An Updated Coupled Model for Land-Atmosphere Interaction. Part Ⅱ: Simulations of Biological Processes

In Part Ⅰ, the authors succeeded in coupling the spectral atmospheric model (SAMIL_R42L9) developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP/CAS) with the land surface model, Atmosphere-Vegetation-Interaction-Model (AVIM) and analyzed the climate basic state and land surface physical fluxes simulated by R42_AVIM. In this Part Ⅱ, we further evaluate the simulated results of the biological processes, including leaf area index (LAI), biomass and net primary productivity (NPP) etc. Results indicate that R42_AVIM can simulate the global distribution of LAI and has good consistency with the monthly mean LAI provided by Max Planck Institute for Meteorology. The simulated biomass corresponds reasonably to the vegetation classifications. In addition, the simulated annual mean NPP has a consistent distribution with the data provided by IGBP and MODIS, and compares well with the work in literature. This land-atmosphere coupled model will offer a new experiment tool for the research on the two-way interaction between climate and biosphere, and the global terrestrial ecosystem carbon cycle.     

The sensitivity of the Indian summer monsoon to a global warming of 2��C with respect to pre-industrial times

In this study the potential future changes in different aspects of the Indian summer monsoon associated with a global warming of 2°C with respect to pre-industrial times are assessed, focussing on the role of the different mechanisms leading to these changes. In addition, these changes as well as the underlying mechanisms are compared to the corresponding changes associated with a markedly stronger global warming exceeding 4.5°C, associated with the widely used SRES A1B scenario. The study is based on two sets of four ensemble simulations with the ECHAM5/MPI-OM coupled climate model, each starting from different initial conditions. In one set of simulations (2020?C2200), greenhouse gas concentrations and sulphate aerosol load have been prescribed in such a way that the simulated global warming dioes not exceed 2°C with respect to pre-industrial times. In the other set of simulations (1860?C2200), greenhouse gas concentrations and sulphate aerosol load have been prescribed according to observations until 2000 and according to the SRES A1B scenario after 2000. The study reveals marked changes in the Indian summer monsoon associated with a global warming of 2°C with respect to pre-industrial conditions, namely an intensification of the summer monsoon precipitation despite a weakening of the large-scale monsoon circulation. The increase in the monsoon rainfall is related to a variety of different mechanisms, with the intensification of the atmospheric moisture transport into the Indian region as the most important one. The weakening of the large-scale monsoon circulation is mainly caused by changes in the Walker circulation with large-scale divergence (convergence) in the lower (uppper) troposphere over the Indian Ocean in response to enhanced convective activity over the Indian Ocean and the central and eastern Pacific and reduced convective activity over the western tropical Pacific. These changes in the Walker circulation induce westerly (easterly) wind anomalies at lower (upper) level in the Indian region. The comparison with the changes in the Indian summer monsoon associated with a global warming of 4.5°C reveals that both the intensification of the monsoon precipitation and the weakening of the large-scale monsoon circulation (particularly in the lower troposphere) are relatively strong (with respect to the magnitude of the projected global warming by the end of the twentieth century for the two scenarios) in the scenario with a global warming of 2°C. The relatively strong intensification of the monsoon rainfall is related to rather strong increases in evaporation over the Arabian Sea and the Bay of Bengal, while a rather weak amplification of the meridional temperature gradient between the Indian Ocean and the land areas to the north contributes to the relatively strong reduction of the large-scale monsoon flow.     

Documentation of a highly ENSO‐related sst region in the equatorial pacific: Research note

Abstract

A new ENSO SST index is documented that is strongly correlated to the core ENSO phenomenon. The SST anomaly in much of the east‐central and eastern tropical Pacific is closely related to ENSO. However, the anomaly from approximately the centre of the eastern half of the equatorial Pacific westward to near the date line is suggested to be most strongly ENSO‐related when data spanning the most recent several decades are used. This is the case both with respect to (1) strength of association with other oceanic/atmospheric ENSO‐related anomalies (both simultaneously and as a time‐delayed predictand), and (2) impact on remote worldwide climate anomalies. This observational insight was lacking in the early 1980s when the four “Niño” regions were developed. While a firmer dynamical foundation for this regional preference still needs to be established, the region straddling Niño 3 and Niño 4 may be regarded as an appropriate general SST index of the ENSO state by researchers, diagnosticians and forecasters. A dataset of this index, called “Niño 3.4” (5°N‐5°S, 120–170°W), is maintained on the Internet, shown in the Climate Diagnostics Bulletin, and provided in the Appendix of this note.     

Summertime land–sea thermal contrast and atmospheric circulation over East Asia in a warming climate—Part II: Importance of CO2-induced continental warming

In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land–sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land–sea SAT contrast in the transient warming simulations of coupled atmosphere–ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO₂ concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land–sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO₂-induced continental warming. The degree of strengthening of the land–sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO₂-induced positive and SST-induced negative contributions to the land–sea contrast. These results imply that changes of climate patterns over the land–ocean boundary regions are sensitive to future scenarios of CO₂ concentration pathways including extreme cases.     

Torneträsk tree-ring width and density ad 500–2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers

This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period ad 500–2004. By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved low-frequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April–August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63–64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around ad 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around ad 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on ad 1000 was significantly warmer than the late-twentieth century (p < 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this “Medieval Warm Period” in northern Fennoscandia was much warmer than previously recognized.     

Applications of AMSR-E Measurements for Tropical Cyclone Predictions Part Ⅰ: Retrieval of Sea Surface Temperature and Wind Speed

Existing satellite microwave algorithms for retrieving Sea Surface Temperature(Sst)and wind(SSW)are applicable primarily for non-raining cloudy conditions.With the launch of the Earth Observing System (EOS)Aqua satellite in 2002,the Advanced Microwave Scanning Radiometer(AMSR-E)onboard provides some unique measurements at lower frequencies which are sensitive to ocean surface parameters under ad-verse weather conditions.In this study,a new algorithm is developed to derive SST and SSW for hurricane predictions such as hurricane vortex analysis from the AMSR-E measurements at 6.925 and 10.65 GHz.In the algorithm,the effects of precipitation emission and scattering on the measurements are properly taken into account.The algorithm performances are evaluated with buoy measurements and aircraft dropsonde data.It is found that the root mean square (RMS) errors for SST and SSW are about 1.8K and 1.9m s(-1),respectively,when the results are compared with the buoy data over open oceans under precipitating clouds (e.g.,its liquid water path is larger than 0.5 mm),while they are 1.1 K for SST and 2.0 ms(-1)for SSW,respectively,when the retrievals are validated against the dropsonde measurements over warm oceans.These results indicate that our newly developed algorithm catl provide some critical surface information for trop-ical cycle predictions.Currently,this newly developed algorithm has been implemented into the hybrid variational scheme for the hurricane vortex analysis to provide predictions of SST and SSW fields.