Explore the vast range of titles available.

A limited area convection permitting model (CPM) based on the Met Office Unified Model, with a 0.04° (4.4 km) horizontal grid spacing, is used to simulate an entire warm-season of the East Asian monsoon (from April to September 2009). The simulations are compared to rain gauge observations, reanalysis and to a lower resolution regional model with a 0.12° (13.2 km) grid spacing that has a parametrization of subgrid-scale convective clouds and precipitation. The 13.2 km simulation underestimates precipitation intensity, produces rainfall too frequently, and shows evident biases in reproducing the diurnal cycle of precipitation and low-level wind fields. In comparison, the CPM shows significant improvements in the spatial distribution of precipitation intensity, although it overestimates the intensity magnitude and has a wet bias over central eastern China. The diurnal cycle of precipitation over Mei-yu region, southern China and the eastern periphery of the Tibetan Plateau, as well as the diurnal cycle of low-level winds over both the Mei-yu region and southern China are better simulated by the CPM. Over the Mei-yu region, in both simulations and observations, the local atmospheric instability in the afternoon is favorable for upward motion and rainfall. The CPM receives more sensible heat flux from the surface, has a stronger upward motion, and overestimates water vapor convergence based on moisture budget diagnosis. All these processes help explain the excessive late afternoon rainfall over the Mei-yu region in the CPM simulation.

Projections for near-surface soil moisture content in Europe for the 21st century were derived from simulations performed with 26 CMIP5 global climate models (GCMs). Two Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered. Unlike in previous research in general, projections were calculated separately for all four calendar seasons. To make the moisture contents simulated by the various GCMs commensurate, the moisture data were normalized by the corresponding local maxima found in the output of each individual GCM. A majority of the GCMs proved to perform satisfactorily in simulating the geographical distribution of recent soil moisture in the warm season, the spatial correlation with an satellite-derived estimate varying between 0.4 and 0.8. In southern Europe, long-term mean soil moisture is projected to decline substantially in all seasons. In summer and autumn, pronounced soil drying also afflicts western and central Europe. In northern Europe, drying mainly occurs in spring, in correspondence with an earlier melt of snow and soil frost. The spatial pattern of drying is qualitatively similar for both RCP scenarios, but weaker in magnitude under RCP4.5. In general, those GCMs that simulate the largest decreases in precipitation and increases in temperature and solar radiation tend to produce the most severe soil drying. Concurrently with the reduction of time-mean soil moisture, episodes with an anomalously low soil moisture, occurring once in 10 years in the recent past simulations, become far more common. In southern Europe by the late 21st century under RCP8.5, such events would be experienced about every second year.

Convection-permitting regional climate models have been shown to improve precipitation simulation in many aspects, such as the diurnal cycle, precipitation frequency, intensity and extremes in many studies over several geographical regions of the world, but their skill in reproducing the warm-season precipitation characteristics over the East Asia has not been robustly tested yet. Motivated by recent advances in computing power, model physics and high-resolution reanalysis, we use the convection-permitting weather research and forecasting (WRF) model configured with 3 km grid spacing to simulate the warm-season precipitation in eastern China for 10 seasons (2008–2017). The hourly 31-km-resolution ERA5 reanalysis data are used to provide initial and boundary conditions for the simulations. The objectives are (1) to evaluate the model skill in simulating warm-season precipitation climatology in the East Asian monsoon region, (2) to identify the promises and problems of the convection-permitting simulation, and (3) to investigate solutions for the model deficiencies. Results demonstrate that the 3-km-resolution WRF model reasonably reproduces the spatial characteristics of seasonal and sub-seasonal precipitation, the seasonal meridional migration associated with the summer monsoon activity, the diurnal variation phase and amplitude, and the propagating convection east of the Tibetan Plateau. The major deficiency is that the model overestimates precipitation amount, especially in the afternoon. Analysis and sensitivity experiments suggest that improved treatment of sub-grid cloud fraction and the aerosol effects may help to suppress the oft-reported high precipitation bias. These results provide useful guidance for improving the model skill at simulating warm-season precipitation in East Asia.

Annual screenings of forage grasses and legumes for shade tolerance were conducted from 1996 to 2001 in the outdoor Shade Tolerance Screening Laboratory at the Horticulture and Agroforestry Research Center, University of Missouri. Forty-three forages were grown under non-shade (100% of full sunlight), moderate shade (45%), and dense shade (20%) without competition for water and nutrients. Annual forage yield (g pot−1) was equal to or higher under moderate shade for all 43 forages and under dense shade for 31 forages than the non-shade control. Relative distance plasticity index (RDPI), a measure of a species’ adaptability to different environments, ranged from 0.104 to 0.567. Cool season grasses had the lowest RDPI (0.183), followed by warm season grasses (0.252), warm season legumes (0.274), and cool season legumes (0.314), indicating grasses tend to be more shade tolerant than legumes in terms of forage yield. Overall, most grass and legume forages have the potential to produce equivalent or higher yields in agroforestry practices featuring light to moderate shade than forages in open pastures when competition from tree roots is minimized.

Mesoscale convective systems (MCSs) are important warm-season precipitation systems in eastern China. However, our knowledge of their climatology and capability in their simulation is still insufficient. This paper examines their characteristics over the 2008–2017 warm seasons using convection-permitting climate simulations (CPCSs) with a 3-km grid spacing that explicitly resolves MCSs, as well as a high-resolution gauge-satellite merged precipitation product. An object-based tracking algorithm is applied to identify MCSs. Results indicate that the MCS genesis and occurrence are closely related to the progression of the East Asian monsoon and are modulated by the underlying topography. On average, about 243 MCSs are observed each season and contribute 19% and 47% to total and extreme warm-season precipitation. The climatological attributes and variabilities are reasonably reproduced in the CPCS. The major model deficiencies are excessive small MCS occurrence and overmuch MCS rainfall, consequently overestimating the precipitation contributions, whereas observational uncertainties may play a role too. Both the observed and simulated MCS precipitation feature a nocturnal or morning maximum and an eastward delayed diurnal peak east of the Tibetan Plateau, in contrast to the dominant afternoon peak of non-MCS precipitation. The favorable comparison with observations demonstrates the capability of CPCSs in simulating MCSs in the Asian monsoon climate, and its usefulness in projecting the future changes of MCSs under global warming. The finding that non-MCS precipitation is responsible for the high biased afternoon precipitation provides helpful guidance for further model improvement.

The intraseasonal (IS) variability of the sea surface temperature (SST) in the Southwestern Atlantic Continental Shelf (SWACS, 45–33° S—70–50° W), and its relationship with that in the atmosphere, was studied for the austral warm season. SST satellite data (11-km resolution NOAA CoastWatch Program) and data of different atmospheric variables (Reanalysis1 NCEP/NCAR and ERA-Interim) were used. Data were filtered using a 10–90 day filter to isolate the IS variability. A Principal Component analysis was applied then to the filtered SST anomalies (SSTA) and the activity of the leading modes was described through the corresponding temporal series. The first three modes are significant. EOF1 (25.7% of variance) exhibits SSTA of opposite sign to the north/south of 42° S. EOF2 (9.0%) and EOF3 (5.1%) are related with centers of SSTA of opposite sign located off the Uruguayan coast and in the middle shelf. Composites of SSTA and of key atmospheric variables were made considering the days in which the main modes were active. They show that the SSTA described by the three modes are associated with distinctive regional sea level pressure anomalies that, in turn, seem to be related to atmospheric Rossby wave trains extending from the Australia area towards South America. The corresponding atmospheric wave sources vary depending on the mode. These results show, therefore, that the SSTA in the SWACS exhibit significant IS variability that is, in part, locally and remotely influenced by atmospheric anomalies oscillating on similar timescales. These ocean–atmosphere teleconnections could help to improve ocean predictability at those timescales in the future.

High-resolution hydroclimate proxy records are essential for distinguishing natural hydroclimate variability from possible anthropogenically-forced changes, since instrumental precipitation observations are too short to represent the whole spectrum of natural variability. In Northern Europe, progress in this field has been hampered by a relative lack of long and truly moisture-sensitive proxy records. In this study, we provide the first assessment of the dendroclimatic potential of Blue Intensity (BI) and partial ring-width measurements (latewood and earlywood width series) from a network of cold and drought-prone Pinus sylvestris L. sites in Sweden. Our results show that all tree-ring parameters and sites share a clear and strong sensitivity to warm-season precipitation. The ΔBI parameter, in particular, shows considerable potential for hydroclimate reconstructions, here permitting a cross-validated precipitation reconstruction capable of explaining 56% (1901–2010 period) of regional-scale warm-season high-frequency precipitation variance. Using ΔBI as an alternative to ring-width improves the predictive skill with nearly a 20 percentage points increase in explained variance, reduces signal instability over time as well as allows a broader seasonal window (May–July) to be reconstructed. Additionally, we found that earlywood BI also reflect a positive late winter through early summer temperature signal. These findings emphasize that tree-rings, and in particular wood density parameters such as from BI, are capable of providing fundamental information to advance our understanding of hydroclimate variability in regions with a cool and rather humid climate regime that traditionally has been overlooked in studies of past droughts. Increasing the spatio-temporal coverage of hydroclimate records in northern Europe, and taking full advantage of the opportunities offered by the wood densitometric properties should be considered a research priority.

Diurnal variations in precipitation, clouds and other related fields are of interest for many applications. Here I analyze surface and satellite observations and ERA5 data to quantify these variations and evaluate ERA5’s performance. Results show that ERA5 captures the observed seasonal climatology of precipitation and cloud amount remarkably well. Surface observations show that warm-season precipitation exhibits a robust diurnal cycle with an amplitude of ~ 20 to 50% of the daily mean and a peak around 14–18 local solar time (LST) over most land areas and 04–08 LST over most oceans. ERA5 approximately reproduces these features with a slightly earlier peak (by ~ 2 h) over both land and ocean and a stronger amplitude over land, mainly due to biases in its convective precipitation. The IMERG satellite product captures mainly the diurnal cycle of convective precipitation with a peak around 16–20 LST during the warm season. ERA5 oceanic precipitation shows robust diurnal variations that are comparable to observations despite its dampened marine surface diurnal cycle due to its use of daily-mean SST. This suggests a free-tropospheric control of oceanic precipitation diurnal cycle. Surface and satellite observations show more clouds (mainly from low clouds) during daytime (nighttime) over land (ocean). ERA5 total cloud diurnal anomalies are more comparable to surface observations than to ISCCP satellite product. Cloud base height shows a minimum in early afternoon and a maximum around midnight with a diurnal amplitude of ~ 150 m over warm-season land in surface observations; ERA5 approximately captures this diurnal cycle with a slightly stronger amplitude and earlier phase. Land planetary boundary layer height (PBLH) in ERA5 is around 250 m at night but increases after sunrise to a peak around 14–15 LST of about 1500–1900 m in the warm season and ~ 650 to 1100 m in the cold season, with largest diurnal amplitudes over summer drylands. ERA5 marine PBLH is higher in the cold season (~ 1000 m) than in the warm season (~ 530 m) in the extra-tropics, suggesting a dominant role by low-level wind-induced mixing. ERA5 CAPE shows out-of-phase diurnal variations over land and ocean, with near-noontime peak (minimum) and an early morning minimum (peak) over land (ocean). ERA5 CIN’s diurnal cycle is approximately out of phase with CAPE. ERA5 captures well the diurnal cycles and their land–ocean and seasonal differences in surface net shortwave and longwave (LWnet) radiation seen in CERES satellite product, with a near-noontime peak in land LWnet. A near-noontime peak is also seen in ERA surface sensible and latent heat fluxes over land, while oceanic PBLH, LWnet and heat fluxes show little diurnal variation in ERA5, which may be partly due to its use of daily-mean SST.

Southwest China frequently witnesses heavy precipitation during warm seasons (May-October) under the joint influence of complex topography and diverse circulation patterns. Based on the objective classification method of spectral clustering, this study identifies three dominant circulation backgrounds and investigates their pivotal roles in determining the warm-season precipitation around Cang Mountain, a complex terrain region in southwest China. Results show that the precipitation characteristics under the three typical circulation patterns are modulated by different dynamic and thermodynamic processes, and each of which has its own seasonality and diurnal variations. Cluster 1 reveals that the northeasterly winds generated by the low-level shear line and vortex on the east side of the Tibetan Plateau provide favorable dynamic conditions for the southwestward evolution of precipitation. As the zonal (meridional) components of northeasterly winds are intensified in the nighttime (daytime), the diurnal cycle of precipitation is manifested with a major (secondary) peak in the early morning (late afternoon). Cluster 2 is featured by the northward advance of the Western Pacific Subtropical High (WPSH) and the monsoon trough over the tropical region. Moreover, there is a high frequency of intense precipitation influenced by the relatively strong thermal instability. With the low-level southeasterly winds strengthening upstream of Cang Mountain at night, the diurnal cycle of precipitation exhibits a pronounced early-morning peak. In Cluster 3, southwesterly winds prevail around Cang Mountain under the configuration of the Indian-Myanmar trough and the strengthened WPSH. The precipitation shows a high percentage of weak intensity due to the relatively weak unstable stratification. These findings offer valuable insights into how circulation patterns impact the fine-scale precipitation processes over complex terrains.

Due to the complexity of built environment, urban design patterns considerably affect the microclimate and outdoor thermal comfort in a given urban morphology. Variables such as building heights and orientations, spaces between buildings, plot coverage alter solar access, wind speed and direction at street level. To improve microclimate and comfort conditions urban design elements including vegetation and shading devices can be used. In warm-humid Dar es Salaam, the climate consideration in urban design has received little attention although the urban planning authorities try to develop the quality of planning and design. The main aim of this study is to investigate the relationship between urban design, urban microclimate, and outdoor comfort in four built-up areas with different morphologies including low-, medium-, and high-rise buildings. The study mainly concentrates on the warm season but a comparison with the thermal comfort conditions in the cool season is made for one of the areas. Air temperature, wind speed, mean radiant temperature (MRT), and the physiologically equivalent temperature (PET) are simulated using ENVI-met to highlight the strengths and weaknesses of the existing urban design. An analysis of the distribution of MRT in the areas showed that the area with low-rise buildings had the highest frequency of high MRTs and the lowest frequency of low MRTs. The study illustrates that areas with low-rise buildings lead to more stressful urban spaces than areas with high-rise buildings. It is also shown that the use of dense trees helps to enhance the thermal comfort conditions, i.e., reduce heat stress. However, vegetation might negatively affect the wind ventilation. Nevertheless, a sensitivity analysis shows that the provision of shade is a more efficient way to reduce PET than increases in wind speed, given the prevailing sun and wind conditions in Dar es Salaam. To mitigate heat stress in Dar es Salaam, a set of recommendations and guidelines on how to develop the existing situation from microclimate and thermal comfort perspectives is outlined. Such recommendations will help architects and urban designers to increase the quality of the outdoor environment and demonstrate the need to create better urban spaces in harmony with microclimate and thermal comfort.