ABSTRACTSummer precipitation in the northern China monsoon region (NCMR; 35°–55°N, 108°–135°E) shows significant intraseasonal variability. The early-summer (June) and late-summer (July–August) precipitation patterns show clear differences in their formation mechanisms and the systems that affect them. We used empirical orthogonal function (EOF) analysis to investigate the two leading modes of July–August precipitation over the NCMR and their associated atmospheric circulation anomalies using linear regression. The results show that the first (EOF1) and second (EOF2) modes correspond to a pan-NCMR precipitation variation pattern and a precipitation oscillation pattern between North China (NC) and Northeast China (NEC), respectively. These two modes account for 22.1% and 10.1% of the total variance, respectively. The associated principal components (PCs) both have significant interannual variability with a period of 2–4 years. In addition, PC1 has significant interdecadal variability with a period of 20–30 years. Further analysis suggests that EOF1 and EOF2 clearly have a different relationship with the summer monsoon circulation system. In the positive phase of PC1, the East Asian subtropical westerly jet stream (EAWJS) shows a northward trend with higher intensity than normal the blocking high at mid- to high latitudes is inactive; and the western Pacific subtropical high (WPSH) is located to the north of its normal position. The NCMR is controlled by stronger southerly winds, which cause the convergence of water vapour, favouring more precipitation in this region and vice versa. In the positive phase of PC2, the EAWJS swings to the south of Lake Baikal. Significant positive height anomalies exist from western NC to NEC. Significant negative height anomalies occur to the subtropical northwestern Pacific. This indicates that the cold vortex in Northeast China is inactive, the WPSH tends to be weaker and located to the south of its normal position, and NEC (NC) is dominated by anomalous northeasterly (southeasterly) winds. The convergence (divergence) of water vapour in NC (NEC) favours more (less) precipitation in NC (NEC) and vice versa. Therefore, EOF1 is related to the large-scale circulation anomalies over East Asia and the northwest Pacific in July and August, whereas EOF2 is more closely related to the anomalies in the regional circulation over the NCMR and the subtropical northwestern Pacific.

This special issue is dedicated to the international project the Year of Tropics–Midlatitude Interactions and Teleconnections (YTMIT) fostered by the World Meteorological Organization through the S...

The developmental stages of Sargassum along with physicochemical factors affect the Sargassum biomass and, thus, affect the size of the habitat used by various fauna and flora. In this study, Sargassum spp. were collected from four stations in Kuwait coastal waters that are mainly distinguished by their levels of turbidity. Investigations revealed that the effects of season (i.e., temperature and sunlight) and turbidity on differences in Sargassum biomass were significant (chi-square = 6.1, degrees of freedom (df) = 2, p = 0.048), but the effects of Sargassum species (chi-square = 5.4, df = 2, p = 0.067) and their life stages (chi-square = 6.73, df = 4, p = 0.15) on Sargassum biomass were not significant. The lack of significant effects of Sargassum spp. on biomass could be because the majority of the collected Sargassum are of one species, S. angustifolium. As for the effect of life stages on Sargassum biomass, this could be because the majority of the stages encountered are juveniles or spent, which are found almost equally among all species. These stages were encountered particularly in spring and summer, mainly at the medium- and low-turbidity stations. The distribution of Sargassum spp. showed strong localization, in which the species inhabiting high-turbidity stations were different from those inhabiting clear waters. This study revealed that the effects of season and turbidity on Sargassum spp. and their life stages on Sargassum biomass represent a reference point for further monitoring studies in northwestern Arabian Gulf.

The Aquatic Climate Change Adaptation Services Program (ACCASP) was launched in 2011 by Fisheries and Oceans Canada (DFO). The initial five-year programme was renewed for a further two years in 201...

Three years of hourly traffic collision data and associated weather data for the city of Edmonton, Alberta, Canada, were analyzed. Using a matched-pair analysis to compare periods of adverse weather with similar periods without adverse weather, the effect of weather on traffic collisions in Edmonton was assessed. Adverse weather took the form of strong winds (>35 km h−1), precipitation (>0.10 mm h−1), or limited visibility (<1.0 km). Risk ratio (RR) values were calculated to determine the relative increase in accidents resulting from each type of weather, as well as for multiple types of concurrent weather. Analysis was performed for collisions that resulted in property damage only (PDO) and severe collisions that resulted in injuries. To determine whether specific types of collisions were more likely to occur during adverse weather, RR values were determined for multiple types of collisions, such as following too closely or failing to stop at a traffic signal. Our results show that adverse weather affects traffic collisions in a variety of ways. Horizontal visibility less than 200 m and strong winds above 45 km h−1, while relatively infrequent in Edmonton, typically resulted in an increase in overall collisions (RR = 3.40 and 1.17, respectively). Precipitation, which is far more common to Edmonton, posed an increased risk to drivers. The type of precipitation was also clearly a factor. The RR value for PDO collisions was higher during periods of snowfall (1.90) than during periods of rainfall (1.28), but the RR value for collisions resulting in injuries (1.37) was higher than the value for PDO collisions during periods of rainfall. Collisions during snowfall had a higher RR value (1.90) for PDO collisions than for collisions resulting in injuries (1.55), and both were higher than the RR values for either type of collision during rainfall, suggesting that snowfall is a greater threat to driving safety than rainfall. For both precipitation types, a higher rate of precipitation was associated with increased risk and a larger number of collisions. Some collision types were clearly affected by the type of precipitation. Vehicles left the road resulting in property damage at far higher RR values during snowfall (3.36) than during periods of rainfall (1.09). Furthermore, analysis of collision types identify that two collisions with nearly identical actions, stopping at a stop sign and stopping at a traffic signal, have very different risks during adverse weather. Stopping at stop signs appears to be far more difficult than stopping at traffic signals during precipitation events and has a higher associated risk. Lastly, we identify a puzzling concern: our results show that Edmonton drivers do not perceive periods of rainfall as presenting a hazard, resulting in a disproportionately high number of injuries during rainfall.

ABSTRACTThe response of the tropical Indian Ocean (TIO) to greenhouse gases (GHGs) and aerosols are investigated based on historical single-forcing and all-forcing simulations using the Geophysical Fluid Dynamics Laboratory Climate Model, version 3 (GFDL CM3). Results reveal a positive Indian Ocean Dipole (pIOD)-like pattern in GHG forcing but a negative Indian Ocean Dipole (nIOD)-like pattern in aerosol forcing. The GHG-induced pIOD-like pattern features less (more) sea surface temperature (SST) warming over the southeastern (western) TIO, accompanied by equatorial easterly anomalies, as well as a shallower thermocline off Sumatra. The aerosol-induced nIOD-like pattern displays the reverse features, characterized by less (more) SST cooling over the southeastern (western) TIO, anomalous equatorial westerlies, and a deeper thermocline off Sumatra. Although the aerosol-induced pattern appears to resemble a reversal of the GHG-induced pattern, there is a strong asymmetry in the SST changes over the southeastern TIO, where the cooling responding to aerosol forcing exceeds the warming in response to GHG forcing, and a negative SST residual is thus produced. A mixed-layer heat budget analysis suggests that the negative SST residual results mainly from asymmetric responses of shortwave radiation, zonal advection, and diffusion to GHGs and aerosols. For comparison, the formation processes for the negative SST skewness over the southeastern TIO between the internal pIOD and nIOD are also discussed.

ABSTRACTBased on a coupled physical-biogeochemical model of the Yellow and East China Seas (YECS), the influence of biological activity on the seasonal variation of the air–sea CO2 flux is evaluated. The solution of a sensitivity experiment that excludes biological activity is compared with that of a reference experiment that includes the full processes. The comparison reveals that biological activity results in a much stronger seasonal variation of surface dissolved inorganic carbon (DIC) and, hence, the ratio of total alkalinity to DIC in the northern parts of the YECS. The increased ratio resulting from biological DIC consumption contributes to the undersaturated partial pressure of CO2 at the sea surface with respect to the atmosphere, causing the central Yellow Sea in summer and autumn to shift from being a CO2 source to a sink; this same shift also occurs over the Changjiang Bank in summer. In the southern YECS, the biological effect is relatively weak. The comparison further reveals that low water temperature, instead of biological activity, is the dominant factor causing the YECS to become a carbon sink in spring. The biological effect on the variation of DIC (both at the surface and in the water column) differs greatly among the three representative regions of the YECS because of differences in primary production and hydrodynamic conditions. Particle-tracking simulations quantify the regional difference in horizontal advection. In the northern region, weaker horizontal advection causes the longer residence time of low DIC water induced by biological consumption. Over the entire YECS, biological activity contributes to about one-third of the total annual absorption of atmospheric CO2.

ABSTRACTThe Fraser River is the source of most particulate matter in the Strait of Georgia, and its dispersal is modulated by the Fraser’s plume. Here we examine the plume’s shape, location, and area, and the variation of these parameters with changes in wind and river forcing by examining a 13-year time series of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery for the concentration of suspended particulate matter (SPM). Plume shape and its variations are quantified by dividing the 904 images in this time series into subsets showing conditions under specified wind and river flow conditions and forming a composite image for each subset. Quantitative analysis of scalar quantities like plume area and mean plume SPM are based on calculated values for all individual images. The plume area increases linearly with river flow, changing by a factor of 10 between lowest and highest flows. Mean plume SPM also changes with flow but only by a factor of two. The surface area of the plume is almost completely unaffected by wind conditions. Plume location, however, is very sensitive to both wind speed and direction. It can reach across the Strait at highest river flows and is advected either northwest or southeast along the Strait in the same direction as winds on daily time scales. We also estimate the residence time of sediment in the plume to be only a few days, allowing the plume itself to reshape rapidly over short time scales in response to weather conditions.

ABSTRACTThe interdecadal change in the relationship between the El Niño–Southern Oscillation (ENSO) and atmospheric circulation over the North Pacific is investigated using both observational data and an atmospheric general circulation model. There are two prominent modes of winter mid-latitude atmospheric variability in the North Pacific: the West Pacific (WP) teleconnection and the Aleutian Low (AL). The relationship between ENSO and the WP-AL patterns changed notably around the late 1970s. From 1957 to 1975, during the mature phase of ENSO, significant sea surface temperature anomalies (SSTAs) occurred, mainly in the equatorial eastern Pacific Ocean; the associated atmospheric circulation anomaly pattern resembles the negative phase of a WP teleconnection pattern. In contrast, for the 1978–2011 period, significant negative SSTAs were observed in the western and extratropical Pacific in both hemispheres, with some significant positive SSTAs appearing over the eastern Pacific. This is in agreement with the defined regions of a mega-ENSO, the associated atmospheric circulation anomaly pattern resembles the AL mode. Further analysis suggests that a negative–positive anomaly pattern in the 500 hPa geopotential height throughout the entire North Pacific, possibly enhanced by the SSTAs in the extratropical North Pacific associated with the mature phase of ENSO, is responsible for modulating the relationship between ENSO and the North Pacific atmospheric circulation.

The fourth-generation Canadian Regional Climate Model’s (CRCM4) precipitable water is evaluated and compared with observational data and ERA-Interim reanalysis data over five Canadian basins with simulations driven by ERA-Interim (two) and global climate models (two). Considering the 22 years of data available in the observations, we analyze precipitable water’s behaviour through its annual cycle, its daily distribution, and its annual daily maxima. For the simulations driven by reanalyses, differences in annual daily maximum values and their correlations with observations are examined. In general, the values for precipitable water simulated by CRCM4 are similar to those observed, and the model reproduces both the interannual and inter-basin variabilities. The simulation at 15 km resolution produces higher extreme values than simulations performed at 45 km resolution and higher than the observations taken at coarser resolution (1°), without much influence on the mean behaviour. Some underestimation is found with the simulation driven by the Canadian Centre for Climate Modelling and Analysis Model, version 3, a sign of a cold and dry bias, whereas the run driven by the European Centre Hamburg Model, version 5, is much closer to the observations, pointing to the importance of closely considering the regional–global model combination. Overall, CRCM4's ability to reproduce the major characteristics of observed precipitable water makes it a possible tool for providing precipitable water data that could serve as a basis for probable maximum precipitation and probable maximum flood studies at the basin scale.