Seasonal Synchronization Research Articles

Melatonin and Seasonal Synchrony in Mammals.

In mammals, seasonal opportunities and challenges are anticipated through programmed changes in physiology and behavior. Appropriate anticipatory timing depends on synchronization to the external solar year, achieved through the use of day length (photoperiod) as a synchronizing signal. In mammals, nocturnal production of melatonin by the pineal gland is the key hormonal mediator of photoperiodic change, exerting its effects via the hypothalamopituitary axis. In this review/perspective, we consider the key developments during the history of research into the seasonal synchronizer effect of melatonin, highlighting the role that the pars tuberalis-tanycyte module plays in this process. We go on to consider downstream pathways, which include discrete hypothalamic neuronal populations. Neurons that express the neuropeptides kisspeptin and (Arg)(Phe)-related peptide-3 (RFRP-3) govern seasonal reproductive function while neurons that express somatostatin may be involved in seasonal metabolic adaptations. Finally, we identify several outstanding questions, which need to be addressed to provide a much thorough understanding of the deep impact of melatonin upon seasonal synchronization.

Local feedback and ENSO govern decadal changes in variability and seasonal synchronization of the Indian Ocean Dipole

The Indian Ocean Dipole (IOD), characterized by an interannual fluctuation in zonal dipole pattern of sea surface temperature anomalies along the tropical Indian Ocean, has a large socioeconomic impact on neighboring countries. Here, we investigate the decadal modulations of IOD variability over the last 123 years (1900–2022), by analyzing the observational reanalysis data in conjunction with a low-order IOD model that accounts for both stochastic forcing and the remote impact of ENSO. The observed decadal changes in IOD variability are primarily attributed to the local air–sea coupled feedback, and secondarily to ENSO. The local feedback during the late winter has intensified since the late-1970s due to the Indian Ocean warming, the suppressed westerly winter monsoon in the southeastern Indian Ocean, the shallowing of the mean thermocline in the southeastern Indian Ocean, and the decrease in mean upwelling in the western Indian Ocean. Each of these enhances the convective instability, anomalous evaporative cooling, and oceanic vertical thermal advections, respectively. Intensified local feedback increases the likelihood of the early onset of IOD events in the late winter. Additionally, ENSO, which has strengthened since the mid-twentieth century, has extended the peak phase of IOD into the late fall in recent decades.

Asynchronous contributions of decapod life history stages to the zooplankton of tropical estuarine, coastal and shelf ecosystems - new insights from semi-automatic image analysis

Decapod crustaceans include many species of socioeconomic importance and are key components of pelagic ecosystems, both as adults and as larval forms. Knowledge on seasonal and spatial synchronicity of planktonic larvae in coastal tropical ecosystems is fundamental to understand the dynamics of these complex ecosystems. The objective of the present study was to quantify the contributions of decapods to the zooplankton in adjacent tropical estuarine, coastal and shelf ecosystems, while considering their seasonal life cycles and probable dispersal strategies. We evaluated the contributions of decapod biomass and biovolume in three distinct ecosystems: Rio Formoso estuary, Tamandaré bay, and Pernambuco continental shelf off Tamandaré, northeastern Brazil. Zooplankton samples were taken bimonthly from June 2013 to May 2015, with a 300 μm mesh net, and analyzed using a ZooScan equipment. Decapods were the second most important organisms (after copepods), in abundance, biomass and biovolume, in all sampling areas. Total decapods contributed on average with 33.6%, 4.4% and 7.1% relative abundance and 30.9%, 30.9%, and 15.2% relative biovolume in estuary, bay, and shelf areas, respectively. Overall, the most relevant decapod taxa and stages found in the three sampling areas were brachyuran crab zoeae and megalopae, penaeid shrimp postlarvae (mostly Penaeus spp.), holoplanktonic luciferids (adults, protozoeae and mysis), anomuran zoeae (mostly Paguridae and Diogenidae hermit crabs), pistol shrimp zoeae (Alpheidae), and porcelain crab zoeae (Porcellanidae). Brachyuran zoeae contributed with up to 81.3% abundance and up to 69% biovolume, in the estuary. Penaeid postlarvae comprised up to 28.1% of total abundance and up to 94.7% of total biovolume, on the shelf. These postlarvae were transported shorewards from the offshore shelf. Decapod contributions were especially relevant during massive larval release events of crab zoeae and during shoreward migration of pre-settlement stages. Seasonal peaks were clearly asynchronous between taxa and areas. Possible functional relationships between copepods and key decapod groups are discussed, as well as the processes triggering and regulating the input of larvae. Our results show the importance of quantitative, semi-automatic approaches and the relevance of decapod larvae for pelagic food webs in tropical coastal areas.

Destabilization of a seasonal synchronization in a population model with a seasonally varying Allee effect

Climate change causing large seasonal fluctuations is likely to lead to an increase in the average threshold of the Allee effect as well as an increase in its seasonal variability. In this paper, we show that a seasonally synchronized predator-prey system can be strongly destabilized by these changes in the threshold of the Allee effect. The typical result first leads to two-year and multiyear cycles by the principle of period doubling on a folded Möbius strip, up to the emergence of a chaotic and hyper-chaotic attractor living close to the trivial equilibrium corresponding to the extinction of populations. Moreover, this instability of the ecosystem can be hidden for a long time and the transition to its basin of attraction can occur by external perturbation in a random and irreversible manner. We also reveal a double folding of the 1:1 synchronized cycle manifold inside the corresponding Arnold tongue and hysteresis similar to well-known Duffing oscillator.

Quasi-biennial modulation of total ozone distribution from equator to polar regions based on observations

The modulation of total ozone (TOZ) by the quasi-biennial oscillation (QBO) not only at the equator, but also at subtropics, middle and high latitudes has long been known. As well, a large number of studies have shown seasonal synchronization and interhemispheric asymmetry of QBO effects in the TOZ in extratropical regions. However, the proposed mechanisms of seasonality and asymmetry as a consequence of the interaction of the quasi-biennial and annual cycles are not well understood. A great problem in comparing model simulations with observations and, hence, in verifying theoretical assumptions about the mechanism of extratropical ozone QBO, is the continually changing phase relationship between the annual and quasi-biennial cycles. This issue is exacerbated by the fact that, as is commonly believed, the wind QBO period is not constant, but varies irregularly from one cycle to another. In this study the influence of the QBO of equatorial stratospheric wind on the global distribution of the TOZ has been analyzed using the SBUV Merged Ozone Data Set (MOD). The investigation of the QBO effects in the TOZ in the subtropics, middle and high latitudes of both hemispheres is based on accounting for the seasonal regularities of the wind QBO, which leads to a limited number of only certain combinations of the quasi-biennial and annual cycles that can be realized. The smaller variability serves to clarify the nature of changes in extratropical ozone. A detailed analysis of the TOZ data for 1970–2021 showed that the interannual TOZ variability at subtropics, middle and high latitudes depends on the alternation of wind QBO cycles of different scenarios. The key moments of the TOZ variations are clearly associated with certain points in time during the downward propagation of the easterly and westerly QBO wind regimes and the seasonally dependent QBO circulation produced by them. These results contradict the general view that it is difficult to isolate the effect of QBO on the TOZ in extratropics because of the irregularly varying QBO period, and can be used in comparing simulated and observed extratropical ozone QBO, as well as in long-term forecast of variations in the TOZ distribution.

Seasonally Modulated El Niño Precipitation Response in the Eastern Pacific and Its Dependence on El Niño Flavors

Abstract Many previous studies have shown that El Niño exhibits a strong seasonality in its teleconnections and regional climate impacts. Aside from the seasonal synchronization of El Niño anomalous sea surface temperature (SST) itself, seasonal differences in its associated climate impacts could also stem from the local background seasonal cycle. During the El Niño developing boreal autumn (August–October) and decaying boreal spring (February–April), the El Niño–associated precipitation anomalies display remarkably different patterns over the eastern tropical Pacific despite similar SST anomaly amplitudes. This strong seasonality can be largely attributed to the seasonal cycle of the eastern tropical Pacific SST background state with the cold tongue being strongest in autumn and weakest in spring. Therefore, the El Niño–associated SST in spring is likely to exceed the convection threshold on both sides of the equator, leading to an approximately symmetric precipitation response about the equator. In contrast, this symmetric precipitation response is absent in autumn since the SST near and south of the equator remains below the threshold and pronounced eastern tropical precipitation anomalies can only be observed in the warm Northern Hemisphere. This seasonality is mainly embodied in eastern Pacific (EP) El Niño events rather than central Pacific (CP) El Niño events since the westward-shifted warm SST anomalies for the latter cannot establish an effective cooperation with the cold tongue SST annual cycle. This study has important implications for regional climate prediction by involving the different local precipitation responses over the tropical eastern Pacific.

Positive effect of spring advance on the diet quality of an alpine herbivore.

Changes in vegetation phenology related to global warming are having alarming effects on the life history traits of many herbivore species. Such changes are particularly critical in alpine ecosystems, where strong climate limitations on plant growth make seasonal synchronization imperative for the growth, reproduction and survival of herbivores. However, despite the pivotal role of resource-use strategies on the performances of such species, few studies have explicitly assessed the mechanistic impact of climate change on their diets. We aimed to fill this gap by studying the effect of spring onset on the dietary composition and quality of a medium-size alpine herbivore while considering density-dependent processes and age- and sex-specific differences in foraging behavior. Using an exceptional, long-term (24 years) direct individual-based dietary monitoring of a Pyrenean chamois population (Rupicapra pyrenaica pyrenaica), we showed that ongoing earlier onsets of spring are leading to an earlier access to high-quality forage and therefore a higher diet quality at a fixed date, without apparent changes in diet composition. We also showed that at high densities, intraspecific competition reduced diet quality by driving animals to feed more on woody plants and less on nutritious forbs and graminoids. By assessing the mechanistic effects of global warming on the dietary patterns of species at the center of trophic networks, this study is an essential step for predictive models aiming at understanding the ongoing ecosystem consequences of the global climatic crisis.

Development of the Extratropical Response to the Stratospheric Quasi-Biennial Oscillation

AbstractUsing the Model of an Idealized Moist Atmosphere (MiMA) capable of spontaneously generating a Quasi-Biennial Oscillation (QBO), the gradual establishment of the extratropical response to the QBO is explored. The period and magnitude of the QBO and the magnitude of the polar Holton-Tan (HT) relationship is simulated in a free-running configuration of MiMA, comparable to that in state-of-the-art climate models. In order to isolate mechanisms whereby the QBO influences variability outside of the tropical atmosphere, a series of branch experiments are performed with nudged QBO winds. When easterly QBO winds maximized around 30 hPa are relaxed, an Eliassen-Palm (E-P) flux divergence dipole quickly forms in the extratropical middle stratosphere as a direct response to the tropical meridional circulation, in contrast to the HT mechanism which is associated with wave propagation near the zero wind line. This meridional circulation response to the relaxed QBO winds develops within the first 10 days in seasonally-varying and fixed-seasonal experiments. No detectable changes in upward propagation of waves in the midlatitude lowermost stratosphere are evident for at least 20 days after branching, with the first changes only evident after 20 days in perpetual midwinter and season-varying runs, but after 40 days in perpetual November runs. The polar vortex begins to respond around the 20th day, and subsequently a near-surface response in the Atlantic sector forms in mid-to-late winter runs. These results suggest that the maximum near-surface response observed in mid-to-late winter is not simply due to a random seasonal synchronization of the QBO phase, but also due to the long (short) lag of the surface response to a QBO relaxation in early (mid-to-late) winter.

Seasonal Associations Between Foodborne Campylobacter Infections and Ambient Temperature in US, 2010–2019

Abstract Objectives In order to effectively mitigate the effects of climate change on human health, spatiotemporal relationships between Campylobacter infections and environmental drivers have to be systematically examined to determine whether common seasonal summer peaks observed in Campylobacter infections are well aligned with peaks in raising ambient temperatures. This study aims to evaluate the seasonal relationship between monthly ambient temperature and the monthly Campylobacter infections routinely collected by the CDC Foodborne Diseases Active Surveillance Network (FoodNet) in the United States in 2010–2019. Methods We created time series of monthly Campylobacter infection rates from the FoodNet Fast platform for ten participating states from January 2010 to December 2019 (120 months). We estimated average monthly temperatures for the ten states for the study period using the National Climate and Data Center's Global Summary of the Day database. To assess the seasonal synchronization and determine the lag effect, we used serial cross-correlation analysis. To examine the associations between Campylobacter rates with ambient temperature and adjust for seasonality and trend, we applied a harmonic negative binomial mixed-effects regression model. We also estimated peak timing and amplitude for infections and temperature using the δ-method. Results Serial synchronization between monthly Campylobacter infection rates and ambient temperature was observed in all FoodNet Surveillance states except for California. A one-month delay in peak infection after the peak in temperature was detected in Colorado, Connecticut, Maryland, Minnesota, New Mexico, New York, and Oregon. After adjusting for seasonality and trend across ten states, the relative risk of infection rates increased by 5% with the increase in monthly average temperature by 5.45°C equivalent to a shift from 75th to 95th percentile (95%CI: 1.02–1.09, p < 0.002). Conclusions An increase in monthly average temperature is associated with an increased risk of Campylobacter infection after adjusting for common summer seasonal patterns. Knowledge of the relationship will potentially improve the reliability and accuracy of integrated early warning outbreak forecasts and could guide climate mitigation strategies. Funding Sources None.

Evidence for circadian-based photoperiodic timekeeping in Svalbard ptarmigan, the northernmost resident bird

The high Arctic archipelago of Svalbard (74°-81° north) experiences extended periods of uninterrupted daylight in summer and uninterrupted night in winter, apparently relaxing the major driver for the evolution of circadian rhythmicity. Svalbard ptarmigan (Lagopus muta hyperborea) is the only year-round resident terrestrial bird species endemic to the high Arctic and is remarkably adapted to the extreme annual variation in environmental conditions.1 Here, we demonstrate that, although circadian control of behavior disappears rapidly upon transfer to constant light conditions, consistent with the loss of daily activity patterns observed during the polar summer and polar night, Svalbard ptarmigans nonetheless employ a circadian-based mechanism for photoperiodic timekeeping. First, we show the persistence of rhythmic clock gene expression under constant light within the mediobasal hypothalamus and pars tuberalis, the key tissues in the seasonal neuroendocrine cascade. We then employ a "sliding skeleton photoperiod" protocol, revealing that the driving force behind seasonal biology of the Svalbard ptarmigan is rhythmic sensitivity to light, a feature that depends on a functioning circadian rhythm. Hence, the unusual selective pressures of life in the high Arctic have favored decoupling of the circadian clock from organization of daily activity patterns, while preserving its importance for seasonal synchronization.

Seasonal synchronization of foodborne outbreaks in the United States, 1996\u20132017

Modern food systems represent complex dynamic networks vulnerable to foodborne infectious outbreaks difficult to track and control. Seasonal co-occurrences (alignment of seasonal peaks) and synchronization (similarity of seasonal patterns) of infections are noted, yet rarely explored due to their complexity and methodological limitations. We proposed a systematic approach to evaluate the co-occurrence of seasonal peaks using a combination of L-moments, seasonality characteristics such as the timing (phase) and intensity (amplitude) of peaks, and three metrics of serial, phase-phase, and phase-amplitude synchronization. We used public records on counts of nine foodborne infections abstracted from CDC’s FoodNet Fast online platform for the US and ten representative states from 1996 to 2017 (264 months). Based on annualized and trend-adjusted Negative Binomial Harmonic Regression (NBHR) models augmented with the δ-method, we determined that seasonal peaks of Campylobacter, Salmonella, and Shiga toxin-producing Escherichia Coli (STEC) were tightly clustered in late-July at the national and state levels. Phase-phase synchronization was observed between Cryptosporidium and Shigella, Listeria, and Salmonella (ρ = 0.51, 0.51, 0.46; p < 0.04). Later peak timing of STEC was associated with greater amplitude nationally (ρ = 0.50, p = 0.02) indicating phase-amplitude synchronization. Understanding of disease seasonal synchronization is essential for developing reliable outbreak forecasts and informing stakeholders on mitigation and preventive measures.

Quasi-biennial oscillation of the equatorial total ozone: A seasonal dependence and forecast for 2019–2021

The interannual variability of the total ozone (TOZ) in the equatorial region (5°S – 5°N) has been studied using the satellite daily and monthly data in 1978–2018. The coupling of the equatorial TOZ changes to the quasi-biennial oscillation (QBO) of the zonal wind in the equatorial stratosphere has long been known. However, the detailed analysis of the daily deseasonalized TOZ data over the course of 15 complete wind QBO cycles convincingly showed some new important features of the ozone QBO (ΔTOZ). The key points of the equatorial ΔTOZ variations are clearly linked with the certain time moments during the downward propagation from ~10 to ~70 hPa of the easterly and westerly regimes of the wind QBO. The equatorial ΔTOZ distinctly maximizes when the westerly regime reaches ~70 hPa and the easterly regime appears at ~10 hPa, which occur simultaneously. The times of minima of the equatorial ΔTOZ are less obvious due to the westerly regime appearance at ~10 hPa on the background of the unfinished descent of the easterly regime. Furthermore, the seasonal regularities of the wind QBO causes the seasonal dependence of the ozone QBO in the equatorial region. Maxima of the equatorial ΔTOZ are definitely observed near solstice months (June or December). This result contradicts to the general belief about lack of the seasonal synchronization of the equatorial ozone QBO in contrast to the seasonally synchronized extratropical ozone. However, the coincidence of the equatorial ΔTOZ maxima with solstices and, consequently, their recurrence every 2 or 2.5 years allow a prediction of the equatorial TOZ, based on the long-term forecast of the wind QBO. The ozone QBO forecast for subsequent about two years (2019–2021) is presented.

INCIDENCE OF HYDROMETRA IN GOATS AND THERAPEUTIC EFFECTS

The presence of hydrometra was analyzed on five dairy goat farms (one Saanen and four Alpine) in a period of one to three years, from 2013 to 2016. Total of 3,355 goats were scanned by ultrasound for pregnancy diagnosis after breeding season or out-of-season upon hormonal synchronization. Overall incidence of hydrometra was 1.37%. One farm of Saanen goats demonstrated statistically higher incidence of hydro/pyometra as compared to other four Alpine farms (3.25% vs. 0.56%; p &lt;0.001). Seasonal synchronization of anestric goats and occasional outof-season synchronization in nulliparous Saanen goats probably contributed to higher incidence of this pathological condition (7/67; 10.45%), thus leaving unclear if this results can be attributed to breed affinity and/or to intensive reproductive management. Treatment with double prostaglandin injections and antibiotic treatment of hydrometra/pyometra resulted in relatively good conception rate of 64% (16/25). In conclusion, regular ultrasonography 40-70 days after mating or insemination is of crucial importance for intensive farm reproductive management on large dairy goat farms. After the treatment, significant percentage of goats with hydrometra can be successfully rebred.

Diagnosing the representation and causes of the ENSO persistence barrier in CMIP5 simulations

In this study, the persistence barrier (PB) of the El Nino–Southern Oscillation (ENSO) phenomenon is investigated using reanalysis data and historical simulations of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Both the timing and intensity of the ENSO PB can be quantified using the maximum gradient of autocorrelation decline of Nino sea surface temperature (SST) anomaly indices. Most of the CMIP5 models were found to reasonably reproduce the observed timing of the ENSO PB that typically occurs during the boreal late spring to early summer, and underestimated the PB intensity compared to observations. Furthermore, the PB properties of the Eastern Pacific (EP) ENSO indices were much better represented by the models than those of the Central Pacific (CP) ENSO indices, probably because CP ENSO events are more challenging to simulate than their counterparts. Approximately half of the models can satisfyingly reflect the intensity and timing of PB for indices of EP ENSO and their distinctions from those of the CP ENSO, with a larger uncertainty for the modeled PB timing than intensity. Further diagnosis has revealed the relationship between the ENSO PB intensity and the factors associated with the tropical Pacific background state. The PB intensity exhibits a stronger relationship with the seasonality of the SST amplitude in CP, compared to the SST amplitude, and the strength of seasonal synchronization of EP SST anomalies is highly correlated with the PB intensity. These results suggest that the seasonality of tropical SST variability may fundamentally contribute to the ENSO PB.

Seasonal synchronization of sleep timing in industrial and pre-industrial societies

Artificial light has reshaped human sleep/wake cycle in industrial societies and raised concern on the misalignment of this cycle relative to the light and dark cycle. This manuscript contrasts sleep timing in extratropical, industrial societies (data from eight national time use surveys in countries with Daylight Saving Time —DST— regulations) and Subtropical, pre-industrial societies with and without access to artificial light (data from nine locations coming from seven previous reports) against the cycle of light and dark. Within the two process model of sleep, results show sleep onset and sleep offset keep bound to each other by the homeostatic process. In winter, the photoreceptive process aligns the phase of the sleep/wake cycle to sunrise. As a result the phase increasingly lags with increasing latitude up to a delay of 120 min at 55° latitude. In summer, the homeostatic process still binds sleep onset to speep offset but DST rules in industrialized societies reduce the lag by one third to 40 min at 55° latitude. Sleep timing is then stationary with latitude. The phase of the sleep/wake cycle is then governed by natural trends and no clues of misalignment are revealed.

Size frequency, dispersal distances and variable growth rates of young sharks in a multi-species aggregation.

During a mark-recapture survey from November 2014 until April 2017, 333 neonatal and juvenile blacktip reef sharks Carcharhinus melanopterus and 302 neonatal and juvenile sicklefin lemon sharks Negaprion acutidens were tagged and measured at the uninhabited and isolated St. Joseph Atoll (Republic of Seychelles). Both species demonstrated seasonal reproductive synchronicity and relatively large sizes at birth. Despite the extended times at liberty > 2.5 years, the majority of recaptures were found in close proximity to the initial tagging location (< 500 m). Annual growth rates of C. melanopterus (n = 24) and N. acutidens (n = 62) ranged from 6.6 to 31.7 cm year-1 (mean ± SE; 16.2 ± 1.2 cm year-1 ) and 0.2 to 32.2 cm year-1 (11.8 ± 1 cm year-1 ), respectively and are to date the most variable ever recorded in wild juvenile sharks. High abundances of both species coupled with long-term and repeated recaptures are indicative of a habitat where juveniles can reside for their first years of life. However, large variability in annual growth rates in both species may suggest high intra and interspecific competition induced by a possibly resource limited, isolated habitat.

Nearly identical cycles of the quasi‐biennial oscillation in the equatorial lower stratosphere

AbstractAs a nonlinear dynamical system with limit cycles but subject to periodic forcings associated with the seasonal cycle, the quasi‐biennial oscillation (QBO) displays seasonal modulation such that phase transitions are more likely to occur in certain months than in others. Modulation is distinct from seasonal synchronization, defined as quantized QBO periods and identical cycles. Instead, nearly identical QBO cycles can be identified in the data having similar period, internal structure, and (optionally) timing with respect to the calendar year. Four such categories are found using a spectral phase method based on the 2‐D phase space of the leading rotated principal components (RPCs) of near‐equatorial monthly mean zonal wind in the layer 70–10 hPa. The most prominent category, containing as many as 15 cycles of the 28 observed thus far, is “nearly biennial” with period slightly greater than 24 months. All results, prior to the recent QBO anomaly in Cycle 28, are demonstrated to be statistically stationary in the sense that the RPCs are temporally invariant and insensitive to the inclusion of data to 100 hPa and with higher vertical resolution. Inclusion of Cycle 28 has no effect on the rotated empirical orthogonal functions but a microscopic change in the long‐term average, since strong easterlies are missing in the anomalous cycle. For objective definition of QBO cycles in physical space‐time, westerly onsets in the 40–53 hPa layer are least likely to stall and provide unambiguous starting times. Half of these onsets cluster in April–May, consistent with the seasonal modulation obtained with the spectral phase method.

Analysis of the Southward Wind Shift of ENSO in CMIP5 Models

During the mature phase of El Niño–Southern Oscillation (ENSO) events there is a southward shift of anomalous zonal winds (SWS), which has been suggested to play a role in the seasonal phase locking of ENSO. Motivated by the fact that coupled climate models tend to underestimate this feature, this study examines the representation of the SWS in phase 5 of the Coupled Model Intercomparison Project (CMIP5). It is found that most models successfully reproduce the observed SWS, although the magnitude of the zonal wind stress anomaly is underestimated. Several significant differences between the models with and without the SWS are identified including biases in the magnitude and spatial distribution of precipitation and sea surface temperature (SST) anomalies during ENSO. Multiple-linear regression analysis suggests that the climatological meridional SST gradient as well as anomalous ENSO-driven convective activity over the northwest Pacific both might play a role in controlling the SWS. While the models that capture the SWS also simulate many more strong El Niño and La Niña events peaking at the correct time of year, the overall seasonal synchronization is still underestimated in these models. This is attributed to underestimated changes in warm water volume (WWV) during moderate El Niño events so that these events display relatively poor seasonal synchronization. Thus, while the SWS is an important metric, it is ultimately the magnitude and zonal extent of the wind changes that accompany this SWS that drive the changes in WWV and prime the system for termination.

Seasonal variation and synchronization of sexual behaviors in free-ranging male Tibetan macaques (Macaca thibetana) at Huangshan, China.

Although seasonal breeding has been documented in many non-human primates, it is not clear whether sexual behaviors show seasonal variation among male individuals. To test this hypothesis, the focal animal sampling method and continuous recording were used to investigate seasonal variation and synchronization of sexual behaviors in five male Tibetan macaques (Macaca thibetana) at Mt. Huangshan from Oct 2005 to Sept 2006. Both copulatory and sexually motivated behaviors (i.e., sexual chase, grimace, and sexual-inspection), which were significantly higher in the mating season than non-mating season. Furthermore, seasonal variations of sexual behaviors, including copulatory and sexually motivated behaviors, were synchronized among males. The results shed light on sexual competition and tactics for reproductive success of male M. thibetana and other non-human primates with seasonal breeding.

Simulating the QBO in an Atmospheric General Circulation Model: Sensitivity to Resolved and Parameterized Forcing

Abstract The quasi-biennial oscillation (QBO) of tropical stratospheric zonal winds is simulated in an atmospheric general circulation model and its sensitivity to model parameters is explored. Vertical resolution in the lower tropical stratosphere finer than ≈1 km and sufficiently strong forcing by parameterized nonorographic gravity wave drag are both required for the model to exhibit a QBO-like oscillation. Coarser vertical resolution yields oscillations that are seasonally synchronized and driven mainly by gravity wave drag. As vertical resolution increases, wave forcing in the tropical lower stratosphere increases and seasonal synchronization is disrupted, allowing quasi-biennial periodicity to emerge. Seasonal synchronization could result from the form of wave dissipation assumed in the gravity wave parameterization, which allows downward influence by semiannual oscillation (SAO) winds, whereas dissipation of resolved waves is consistent with radiative damping and no downward influence. Parameterized wave drag is nevertheless required to generate a realistic QBO, effectively acting to amplify the relatively weaker mean-flow forcing by resolved waves.