Seasonal Temperature Cycle Research Articles

Seed germination traits in the rare sandstone rockhouse endemic Solidago albopilosa (Asteraceae)

Understanding how temperature and other environmental cues influence germination traits can aid in the conservation and management of rare plant species. We examined the germination niche of the narrow endemic Solidago albopilosa, a perennial herb restricted to sandstone rockhouses in the southeastern United States. We experimentally subjected seeds to varying lengths of cold stratification, incubation temperatures, photoperiods, and seasonal temperature cycles that simulated current ambient temperatures and a climate warming scenario. Seeds exhibited conditional physiological dormancy and germinated at greater proportions following chilling than when fresh in all temperatures and light regimes tested. In seasonal temperature cycles that simulate those after seed dispersal in late autumn, seeds began germinating after 9 wk in late-winter temperatures (February), with peak germination occurring in early spring (March). Germination timing shifted 1 wk earlier in the spring with climate warming, but germination proportions did not differ among treatments. Buried seeds did not persist to the second germination season (spring), suggesting minimal carryover among years. Seed viability declined in the smallest (< 50 stems) populations but varied less among sites with different levels of human disturbance. A germination niche defined by conditional physiological dormancy, a minimal chilling requirement, dark germination, seasonal germination cueing, and low persistence in the soil is consistent with the expectation of a perennial herb from a stable habitat, but diverges in some aspects from seed traits found in Solidago species of grasslands and open habitats. These results suggest that dormancy or germination do not limit seed regeneration in most natural populations nor contribute to S. albopilosa's rarity.

Climate Change, Temperature, and Homicide: A Tale of Two Cities, 1895–2015

AbstractIt has been argued that the temperature increase caused by anthropogenic climate change will produce a significant increase in violent crime. Support for that prediction is often based on statistical analyses of seasonal temperature and crime data cycles across days, months, and quarters and sometimes on large geographic areas. Within-year temperature changes are very large, however, relative to the 30-yr temperature increases employed to measure climate change. In addition, because temperature trends associated with climate change vary geographically, analyses should employ small geographic units for which temperature changes are measured over yearly intervals and for long periods of time. To address these conditions, this study examined the long-term temperature–crime association for homicides in New York and London for 1895–2015. Consistent with previous studies examining seasonal weather and crime patterns, we found a positive correlation between annual homicide rates and temperature, but only at the bivariate level. This relationship became statistically insignificant in both New York and London when gross domestic product is controlled. Moreover, the bivariate relationship between temperature and homicide is statistically insignificant when correcting for nonstationarity. Thus, it does not appear that climate change has led to higher rates of homicide in New York and London over the long term. These nonfindings are important because they suggest that studies of climate change and violence might do well to consider alternative mechanisms that mediate the relationship between climate change and violence.

Cyst-forming dinoflagellates in a warming climate

Many phytoplankton species, including many harmful algal bloom (HAB) species, survive long periods between blooms through formation of benthic resting stages. Because they are crucial to the persistence of these species and the initiation of new blooms, the physiology of benthic stages must be considered to accurately predict responses to climate warming and associated environmental changes. The benthic stages of dinoflagellates, called resting cysts, germinate in response to the combination of favorable temperature, oxygen-availability, and release from dormancy. The latter is a mechanism that prevents germination even when oxygen and temperature conditions are favorable. Here, evidence of temperature-mediated control of dormancy duration from the dinoflagellates Alexandrium catenella and Pyrodinium bahamense—two HAB species that cause paralytic shellfish poisoning (PSP)—is reviewed and presented alongside new evidence of complementary, temperature-based control of cyst quiescence (the state in which cysts germinate on exposure to favorable conditions). Interaction of the two temperature-based mechanisms with climate is explored through a simple model parameterized using results from recent experiments with A. catenella. Simulations demonstrate the importance of seasonal temperature cycles for the synchronization of cysts’ release from dormancy and are consistent with biogeography-based inferences that A. catenella is more tolerant of warming in habitats that experience a larger range of seasonal temperature variation (i.e., have higher temperature seasonality). Temperature seasonality is much greater in shallow, long-residence time habitats than in deep, open-water ones. As warming shifts species’ ranges, cyst beds may persist longer in more seasonally variable, shallow inshore habitats than in deep offshore ones, promoting HABs that are more localized and commence earlier each year. Recent field investigations of A. catenella also point to the importance of new cyst formation as a factor triggering bloom termination through mass sexual induction. In areas where temperature seasonality restricts the flux of new swimming cells (germlings) to narrow temporal windows, warming is unlikely to promote longer and more intense HAB impacts—even when water column conditions would otherwise promote prolonged bloom development. Many species likely have a strong drive to sexually differentiate and produce new cysts once concentrations reach levels that are conducive to new cyst formation. This phenomenon can impose a limit to bloom intensification and suggests an important role for cyst bed quiescence in determining the duration of HAB risk periods.

Seasonal controls on the diet, metabolic activity, tissue reserves and growth of the cold-water coral Lophelia pertusa

Vast cold-water coral (CWC) reefs occur in temperate regions, where strong seasonality in temperature and light leads to a short but highly productive spring period. How CWCs respond physiologically to this strong seasonal forcing remains unclear, due to the remoteness of their deep-sea habitats. In an in situ transplantation study at Nakken reef, Norway, we investigated a full seasonal cycle of (1) temperature and food availability, (2) diet, (3) biomass and tissue reserves, (4) oxygen consumption and (5) linear growth of the reef-building coral Lophelia pertusa. All investigated variables showed a distinct seasonality. An increase in the organic carbon and amino acid content, linear extension and budding rate from February to late May, at a simultaneous increase in phytoplankton and zooplankton fatty acid trophic markers (FATMs), and δ15N-derived trophic level, indicates an efficient exploitation of the spring phytoplankton and the subsequent zooplankton bloom. A pool of neutral-lipid-derived fatty acids, indicative of energy storage and gametogenesis, was formed from May to October, accompanied by increased oxygen consumption, i.e. metabolic activity. In late autumn and early winter (October–December), tissue reserves were maintained, in spite of low sPOM and zooplankton food availability, and the lower tissue δ13C and higher contribution of bacterial FATMs suggest increased reliance on more degraded material. The concurrent reduction in linear growth further suggests a lower energy availability at this time of the year. A large (> 50%) drop of all tissue pools between December and February coincided with the spawning season of L. pertusa and demonstrates a high energetic cost of reproduction. Our results show for the first time a strong seasonal control of critical life history traits such as growth patterns and timing of reproduction in this prominent deep-sea species.

Growth of Sphagnum is strongly rhythmic: contribution of the seasonal, circalunar and third components.

Among the bryophytes, biological growth rhythms have not yet been identified due to a lack of long‐term precision observations. Here, we carry out precision field monitoring of the growth of the peat moss Sphagnum riparium using the recent geotropic curvature method. For 4 years, using the observation intervals of 2–5 days, we measured 116 469 shoots and received 4493 estimates of growth rates. We found three rhythmic growth components. The seasonal rhythm of growth has a period of about 180 days, which coincides with the seasonal temperature cycle. The circalunar growth rhythm has a period of about 29.5 days and coincides with the synodic lunar cycle. There is an acceleration near the new moon, and a slowdown in growth near the full moon. The third rhythm has a period of 7–16 days and is always synchronized with the circalunar growth rhythm. From the models of the sums of sinusoids, we found that the total contribution of all three rhythms to the growth rate is R2 = 0.51–0.78, and without taking into account the seasonal rhythm, R2 = 0.36–0.42. Thus, our study provides the first data on the biological rhythms and the contribution of these rhythms to the growth process of bryophytes. We attribute the unexpectedly high contribution of rhythms to the synchronous growth of the Sphagnum mat, which is necessary to reduce the loss of moisture.

Coral-inferred monsoon and biologically driven fractionation of offshore seawater rare earth elements in Beibu Gulf, northern South China Sea

We present a monthly dataset (AD 2002–2005) of rare earth elements (REEs) recorded in Porites coral, which were obtained from the Weizhou Island (WZI), Beibu Gulf, northwest of South China Sea (SCS). This offshore coral shows a strong seasonal cycle in REE/Ca ratios, with enriched REEs (total REEs, 100~140 ppb) in winter and depleted REEs (40~60 ppb) in summer. Since the influence of the river discharge is limited to the river mouth, its contribution to the dissolved REEs is negligible for the offshore area of WZI. Given the similar seasonal pattern of Ba/Ca, we suggest that the remobilization of REEs from river-transported sediments on the shelf of SCS through winter monsoon-driven mixing is the major source of REEs to WZI. Moreover, the peak time of the Nd/Yb ratio (occurred in spring) is not coupled with the occurrence of the maximum REEs, which could mainly be attributed to the degradation of biogenic particles that causes more light REE released in comparison to heavy REE. The Ce anomaly also displays a distinct seasonality (i.e., enhanced anomaly in winter and summer and diminished anomaly in spring), likely reflecting the microbial oxidation activities driven by seasonal temperature and nutrient cycles. Large Gd anomaly (Gd/Gd* up to 1.7) recorded in coral skeletons is unlikely originated from the natural sources, but reflects anthropogenic activities through the recent excessive use of Gd complexes by magnetic resonance imaging of medical examination in this region.

Analysis of the changing patterns of seasonal flooding along the U.S. East Coast

Sea level rise (SLR) is causing acceleration in the frequency and duration of minor tidal flooding (often called “sunny-day” or “nuisance” flooding) along the U.S. East Coast. Those floods have a seasonal pattern that often follows the monthly mean sea level anomaly which peaks in September–October for stations between New York and south Florida. However, there are large differences between coasts: for example, over 75% of the minor floods occur during the fall in Florida, but during the spring and winter in Boston. Various data and forcing, such as tide gauge records, surface temperatures, winds, long-term tidal cycles, and the Gulf Stream flow, were analyzed to examine potential drivers and mechanisms that can contribute to the seasonal pattern of floods. The seasonal water temperature cycle, with maximum temperatures in August, could not by itself explain the seasonal sea level pattern, but two mechanisms that significantly correlate with the seasonal sea level and flooding patterns are the annual and semi-annual tidal cycles (correlation of ~ 0.97) and changes in the Gulf Stream (GS) flow (correlation of − 0.6; the GS shows a maximum decline in September–October during the period of peak flooding). The combination of the seasonal pattern of tropical storms and high coastal sea level can explain the high frequency of fall flooding along the Southeastern U.S. coasts, while winter storms have more influence on the northeastern coasts. In recent decades however, the seasonal pattern seemed to have shifted so that increased flooding is seen on the northeastern coasts during spring and summer, while in the Mid-Atlantic and southeastern coasts, a dramatic increase in flooding is seen almost exclusively during the fall. A long-term change in the mean zonal wind pattern along the coast can contribute to the recent shift in the seasonal flooding pattern. The study can help regional adaptation and resilience planning for flood-prone coastal cities and communities.

Projected Changes in Daily Variability and Seasonal Cycle of Near-Surface Air Temperature over the Globe during the Twenty-First Century

AbstractIncreases in atmospheric greenhouse gases will not only raise Earth’s temperature but may also change its variability and seasonal cycle. Here CMIP5 model data are analyzed to quantify these changes in surface air temperature (Tas) and investigate the underlying processes. The models capture well the mean Tas seasonal cycle and variability and their changes in reanalysis, which shows decreasing Tas seasonal amplitudes and variability over the Arctic and Southern Ocean from 1979 to 2017. Daily Tas variability and seasonal amplitude are projected to decrease in the twenty-first century at high latitudes (except for boreal summer when Tas variability increases) but increase at low latitudes. The day of the maximum or minimum Tas shows large delays over high-latitude oceans, while it changes little at low latitudes. These Tas changes at high latitudes are linked to the polar amplification of warming and sea ice loss, which cause larger warming in winter than summer due to extra heating from the ocean during the cold season. Reduced sea ice cover also decreases its ability to cause Tas variations, contributing to the decreased Tas variability at high latitudes. Over low–midlatitude oceans, larger increases in surface evaporation in winter than summer (due to strong winter winds, strengthened winter winds in the Southern Hemisphere, and increased winter surface humidity gradients over the Northern Hemisphere low latitudes), coupled with strong ocean mixing in winter, lead to smaller surface warming in winter than summer and thus increased seasonal amplitudes there. These changes result in narrower (wider) Tas distributions over the high (low) latitudes, which may have important implications for other related fields.

The Oxford 3D thermophysical model with application to PROSPECT/Luna 27 study landing sites

A 3D thermal model that includes a discrete subsurface exponential density profile, surface shadowing and scattering effects has been developed to simulate surface and subsurface temperatures across the Moon. Comparisons of the modelled surface temperatures with the Lunar Reconnaissance Orbiter’s Diviner Lunar Radiometer Experiment (“Diviner”) measured temperatures show significant improvements in model accuracy from the inclusion of shadowing and scattering effects, with model errors reduced from ~10 K to ~2 K for mid-latitude craters. The 3D thermal model is used to investigate ice stability at potential landing sites near the lunar south pole, studied for Roscosmos’ ‘Luna Resource’ (Luna 27) lander mission on which the ESA PROSPECT payload is planned to fly. Water ice is assumed to be stable for long periods of time (>1 Gyr) if temperatures remain below 112 K over diurnal and seasonal cycles. Simulations suggest ice can be stable at the surface in regions near to potential landing sites in permanently shaded regions and can be stable below the surface in partly shaded regions such as pole-facing slopes. The simulated minimum constant subsurface temperature (where the seasonal temperature cycle is attenuated) typically occurs at a depth of ~50 cm and therefore the minimum depth where ice can be stable is 0≤z≲50cm.

Evaluation of multi‐RCM high‐resolution hindcast over the CORDEX East Asia Phase II region: Mean, annual cycle and interannual variations

AbstractBased on the Coordinated Regional Downscaling Experiment‐East Asia second phase (CORDEX‐EA‐II) with higher resolution, model results driven by ERA‐Interim reanalysis using WRF, RegCM4 and CCLM are evaluated against the observational datasets including CN05.1, CRU and GPCP during the period of 1989–2009. The results show that the RCMs have the capability to simulate the annual and seasonal mean surface air temperature and precipitation, however, some biases are produced. The biases are highly dependent on the geophysical locations and the RCMs applied, and CCLM agrees better with the observed precipitation over ocean. CCLM also outperforms the other two RCMs in simulating the interannual variations of temperature and precipitation in most sub‐regions, which can be attributed to its better presentation of the interannual variation of large scale circulation. Generally, all the three RCMs can well reproduce the seasonal cycles of the surface air temperature in most sub‐regions, however, only in the northern regions of China can the RCMs well reproduce the seasonal cycles of precipitation.

Measurement of the cosmic ray muon flux seasonal variation with the OPERA detector

The OPERA experiment discovered muon neutrino into tau neutrino oscillations in appearance mode, detecting tau leptons by means of nuclear emulsion films. The apparatus was also endowed with electronic detectors with tracking capability, such as scintillator strips and resistive plate chambers. Because of its location in the underground Gran Sasso laboratory, under 3800 m.w.e., the OPERA detector has also been used as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the measurement of the single muon flux modulation and its correlation with the seasonal cycle of atmospheric temperature is reported.

Performance of SEACLID/CORDEX-SEA multi-model experiments in simulating temperature and rainfall in Vietnam

The study examined the performance of six regional climate experiments conducted under the framework of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment-Southeast Asia (SEACLID/CORDEX-SEA) project and their ensemble product (ENS) in simulating temperature at 2 m (T2m) and rainfall (R) in seven climatic sub-regions of Vietnam. The six experiments were named following the names of their driving Global Climate Models (GCMs), i.e., CNRM, CSIRO, ECEA, GFDL, HADG and MPI. The observation data for the period 1986–2005 from 66 stations in Vietnam were used to compare with the model outputs. Results showed that cold biases were prominent among the experiments and ENS well reproduced the seasonal cycle of temperature in the Northeast, Red River Delta, North Central and Central Highlands regions. For rainfall, all the experiments showed wet biases and CSIRO exhibited the best. A scoring system was elaborated to objectively rank the performance of the experiments and the ENS experiment was reported to be the best.

Relationship between air temperature and horizontal sand-dust flux observed in the Taklimakan Desert, China

Over the hinterland of the Taklimakan Desert (TD), the diurnal and seasonal cycles of the air temperature (AT) and horizontal sand-dust flux (HSDF) were investigated, based on in situ data including sand saltation counts and meteorological parameters in the period 2008–2010. In particular, the relationship between AT and HSDF was determined. It was found that 74.7% of HSDF was observed between 10:00 and 20:00, and HSDF in spring and summer accounted for 92.3% of the annual flux. Further, the diurnal and annual cycles of HSDF and AT presented an exponential distribution, with correlation coefficients (R) of 0.97 and 0.93, respectively. Additionally, when AT was 0 °C or lower, the frequency of sand saltation was only 4.3%. The maximum sand saltation frequency was 70.1%, which occurred at 33–34 °C, while 67.6% of the total HSDF occurred at 24–34 °C. Finally, a Gauss equation was established over the TD: Q = 250.2 + 1368.5e−2 × [(T−30.8)/7.3]^2, with R = 0.90. Results revealed a strong correlation between HSDF and AT, indicating that AT should be noticeable in HSDF parameterization schemes.

Mid-Holocene climate change over China: model–data discrepancy

Abstract. The mid-Holocene period (MH) has long been an ideal target for the validation of general circulation model (GCM) results against reconstructions gathered in global datasets. These studies aim to test GCM sensitivity, mainly to seasonal changes induced by the orbital parameters (longitude of the perihelion). Despite widespread agreement between model results and data on the MH climate, some important differences still exist. There is no consensus on the continental size (the area of the temperature anomaly) of the MH thermal climate response, which makes regional quantitative reconstruction critical to obtain a comprehensive understanding of the MH climate patterns. Here, we compare the annual and seasonal outputs from the most recent Paleoclimate Modelling Intercomparison Project Phase 3 (PMIP3) models with an updated synthesis of climate reconstruction over China, including, for the first time, a seasonal cycle of temperature and precipitation. Our results indicate that the main discrepancies between model and data for the MH climate are the annual and winter mean temperature. A warmer-than-present climate condition is derived from pollen data for both annual mean temperature (∼0.7 K on average) and winter mean temperature (∼1 K on average), while most of the models provide both colder-than-present annual and winter mean temperature and a relatively warmer summer, showing a linear response driven by the seasonal forcing. By conducting simulations in BIOME4 and CESM, we show that surface processes are the key factors creating the uncertainties between models and data. These results pinpoint the crucial importance of including the non-linear responses of the surface water and energy balance to vegetation changes.

Linking thermal adaptation and life-history theory explains latitudinal patterns of voltinism.

Insect life cycles are adapted to a seasonal climate by expressing alternative voltinism phenotypes-the number of generations in a year. Variation in voltinism phenotypes along latitudinal gradients may be generated by developmental traits at critical life stages, such as eggs. Both voltinism and egg development are thermally determined traits, yet independently derived models of voltinism and thermal adaptation refer to the evolution of dormancy and thermal sensitivity of development rate, respectively, as independent influences on life history. To reconcile these models and test their respective predictions, we characterized patterns of voltinism and thermal response of egg development rate along a latitudinal temperature gradient using the matchstick grasshopper genus Warramaba. We found remarkably strong variation in voltinism patterns, as well as corresponding egg dormancy patterns and thermal responses of egg development. Our results show that the switch in voltinism along the latitudinal gradient was explained by the combined predictions of the evolution of voltinism and of thermal adaptation. We suggest that latitudinal patterns in thermal responses and corresponding life histories need to consider the evolution of thermal response curves within the context of seasonal temperature cycles rather than based solely on optimality and trade-offs in performance. This article is part of the theme issue 'Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen'.

The surface temperature of Europa

Previous estimates of the annual mean surface temperature of Jupiter's moon, Europa, neglected the effect of the eccentricity of Jupiter's orbit around the Sun, the effect of the emissivity and heat capacity of Europa's ice, the effect of the eclipse of Europa (i.e., the relative time that Europa is within the shadow of Jupiter), the effect of Jupiter's radiation, and the effect of Europa's internal heating. Other studies concentrated on the diurnal cycle but neglected some of the above factors. In addition, to our knowledge, the seasonal cycle of the surface temperature of Europa was not estimated. Here we systematically estimate the diurnal, seasonal and annual mean surface temperature of Europa, when Europa's obliquity, emissivity, heat capacity, and eclipse, as well as Jupiter's radiation, internal heating, and eccentricity, are all taken into account. For a typical internal heating rate of 0.05Wm−2, the equator, pole, and the global and mean annual mean surface temperatures are 96 K, 46 K, and 90 K, respectively. We found that the temperature at the high latitudes is significantly affected by the internal heating, especially during the winter solstice, suggesting that measurements of high latitude surface temperatures can be used to constrain the internal heating. We also estimate the incoming solar radiation to Enceladus, the moon of Saturn.

Production and uptake of dissolved carbon, nitrogen, and phosphorus in overlying water of aquaculture shrimp ponds in subtropical estuaries, China.

Water quality deterioration can adversely affect the long-term sustainability of aquaculture industry. Understanding the processes of nutrient regeneration and uptake is important for improving water quality and the overall ecosystem health of aquaculture system. In spite of the importance of dissolved nutrients (DOC, DIC, N-NOx-, N-NH4+, and P-PO43-) in governing water quality and ecosystem functioning, the spatiotemporal variations in the production and uptake of dissolved nutrients in aquaculture ponds is still poorly understood. In this study, the nutrient production and uptake rates in the overlying water were quantified among different shrimp growth stages in the aquaculture ponds in the Min River Estuary (MRE) and Jiulong River Estuary (JRE), southeast China. Significant differences in the nutrient production and uptake rates in the overlying water were observed among the three growth stages and two estuaries. The temporal variations of DOC and DIC production rates in both estuarine ponds closely followed the seasonal cycle of temperature, while the difference in DOC and DIC production rates between the two estuaries was likely caused by differences in water salinity. The changes in the production and uptake rates of dissolved inorganic nitrogen (N-NOx- and N-NH4+) and P-PO43- in the water column over time were partly related to the interactions between thermal conditions and phytoplankton biomass (e.g., chlorophyll a concentrations) in the ponds. Our results demonstrate the complex dynamics and environmental risk of dissolved nutrients in subtropical shrimp ponds, and call for a more effective management of nutrient-laden wastewater in safeguarding the long-term sustainability of aquaculture production.

Effect of Cascading Reservoirs on the Flow Variation and Thermal Regime in the Lower Reaches of the Jinsha River

We analyzed the alteration of discharge and water temperature caused by two newly established reservoirs in the lower reaches of the Jinsha River. In comparison to longer-term observations from the pre-impoundment period, the seasonal flow variability was significantly affected by the larger, upstream-located Xiluodu reservoir, with higher discharge in spring and reduced discharge in summer. The smaller, downstream located Xiangjiaba reservoir did not contribute significantly to the total hydrological alteration caused by the reservoir cascade. Thermal stratification occurred in spring and summer in the Xiluodu reservoir, but was not observed in the Xiangjiaba reservoir. The vertical structure and seasonal dynamics of thermal stratification were mainly governed by the water temperature of the inflow and the depth of the water outlet. Despite the different thermal structure, both reservoirs reduced the amplitude of annual temperature variations and delayed the seasonal temperature cycle in the downstream river water. In contrast to discharge variation, thermal effects were cumulative along the cascading reservoirs. Homogenization and delay effects can be expected to increase further with the completion of ongoing reservoir construction upstream of the two studied reservoirs. Based on our findings, we discuss the larger-scale impacts of cascading hydropower developments and emphasize the need for taking water temperature and its variation into account when developing optimized operation or mitigation strategies for these systems.

Upper ocean high resolution regional modeling of the Arabian Sea and Bay of Bengal

In this paper, effort is made to demonstrate the quality of high-resolution regional ocean circulation model in realistically simulating the circulation and variability properties of the northern Indian Ocean (10°S–25°N, 45°–100°E) covering the Arabian Sea (AS) and Bay of Bengal (BoB). The model run using the open boundary conditions is carried out at 10 km horizontal resolution and highest vertical resolution of 2 m in the upper ocean. The surface and sub-surface structure of hydrographic variables (temperature and salinity) and currents is compared against the observations during 1998–2014 (17 years). In particular, the seasonal variability of the sea surface temperature, sea surface salinity, and surface currents over the model domain is studied. The highresolution model’s ability in correct estimation of the spatio-temporal mixed layer depth (MLD) variability of the AS and BoB is also shown. The lowest MLD values are observed during spring (March-April-May) and highest during winter (December-January-February) seasons. The maximum MLD in the AS (BoB) during December to February reaches 150 m (67 m). On the other hand, the minimum MLD in these regions during March-April-May becomes as low as 11–12 m. The influence of wind stress, net heat flux and freshwater flux on the seasonal variability of the MLD is discussed. The physical processes controlling the seasonal cycle of sea surface temperature are investigated by carrying out mixed layer heat budget analysis. It is found that air-sea fluxes play a dominant role in the seasonal evolution of sea surface temperature of the northern Indian Ocean and the contribution of horizontal advection, vertical entrainment and diffusion processes is small. The upper ocean zonal and meridional volume transport across different sections in the AS and BoB is also computed. The seasonal variability of the transports is studied in the context of monsoonal currents.

The impact of radiation parameterization schemes on the regional climate simulations over the CORDEX-EA domain

This study evaluates the impact of radiation schemes on the regional climate simulations with the WRF (Weather Research and Forecasting) model over the CORDEX-EA (Coordinated Regional Climate Downscaling Experiment-East Asia) domain during 1989–2008. The model is driven by the ERA-Interim reanalysis at a horizontal resolution of 50 km, and the two radiation schemes of CAM (Community Atmosphere Model) and RRTMG (Rapid Radiative Transfer Model for Global Climate Models) are applied. The mean and extreme temperature is generally underestimated by the model over most areas, with the greatest bias reaching 8 °C over the Tibetan Plateau, which can be explained by the underestimation of the long wave radiation. The RRTMG scheme reduces the underestimation of long wave radiation by about 30 W/m2 in most regions, and thus reduces the root mean square error of annual mean temperature over the east Asia domain by about 0.77 °C. The simulations of precipitation show little dependence on the radiation schemes, with slight superiority in the CAM-driven experiment. The model's performance of producing the interannual variation of the temperature can be partly attributed to that of the long wave radiation, and the CAM scheme works slightly better in producing the interannual feature of both temperature and precipitation. The seasonal cycles of both temperature and precipitation are reasonably produced by the model. The cold bias of temperature is found to mainly occur in the cold months through the year, which is probably associated with the greater underestimation of long wave radiation flux in the cold months.