Seasonal Long-term Trends Research Articles

Complexities of urban impacts on long-term seasonal trends in a mid-sized arid city

The variability of surface air temperature is of great importance for both society and the environment, is impacted by global warming and local-scale changes. In the arid eastern part of Washington state of USA, substantial urbanization has transformed the Tri-cities into the state’s third-largest urban cluster. This study utilizes a combination of in situ observations and reanalysis datasets to investigate the influence of land use changes on the region’s 2-meter temperature, revealing local effects that compensate for the background global warming. Within the urban fabric, distinct microclimates have emerged due to varying land use, establishing unique relationships between greenness and temperature alterations caused by land use transitions. Notably, our findings demonstrate that the observed compensating signal in the temperature of farmland locations is primarily attributed to local vegetation increases. Through these observations, this research highlights the urban impacts on local climate, offering valuable insights into the complexities surrounding land use and its consequences on the environment.

The in situ and satellite data blended for reconstruction of the surface salinity of the Sea of Azov

ABSTRACT In this paper, we propose a method for retrieving salinity in the Sea of Azov. The method is based on combining in situ and remote sensing measurements. The operational results of the salinity reconstruction are necessary for the assimilation of thermohaline fields, which is used to set initial conditions to the hydrodynamic model and achieve higher accuracy of its results. The proposed method consists of implementing a general regression between historical in situ measurements and L2 MODIS optical measurements. We used properly calibrated and validated satellite data taken from open internet services. The results show different approaches to obtain the linear regression in spring and summer. Particular emphasis is made on analysing the precision of the reconstructed salinity fields relative to in situ measurements. These estimates are based on the comparison of reconstructed salinity with the long-term seasonal trends on in situ data for the periods of 1990–2018 and 2000–2018. The final reconstructed salinity fields are computed from linear regressions for spring and summer. These reconstructed fields are stored as data sets on a regular grid of the Sea of Azov and they are ready for visualization and use as input data for the ocean circulation models.

Complexities of urban impacts on long-term seasonal trends in a mid-sized arid city

Complexities of urban impacts on long-term seasonal trends in a mid-sized arid city

Assessment of Indian Ocean upwelling changes and its relationship with the Indian monsoon

Present study aims to assess the Indian Ocean upwelling zones and its relationship with the Indian monsoon. Assessment of upwelling zones are examined by using fine resolution satellite sea surface temperature (SST), chlorophyll-a concentration and reanalysis nitrate (NO 3 ), surface wind speed, mean sea level pressure (MSLP) and precipitation products. This study uses the high-resolution (12 km) satellite era reanalysis Indian Monsoon Data Assimilation and Analysis (IMDAA) data for the evaluation of upwelling and summer monsoon relationship. Long-term and decadal trends of SST, chlorophyll-a and NO 3 are estimated by employing the non-parametric Mann–Kendall test and Sen's slope method for the summer monsoon (June–September) and winter monsoon (October–December) season. Long-term seasonal trends suggest the significant warming and weakening of upwelling over western tropical Indian Ocean, however, decadal trends reveals that signal is more prominent during the period 1999–2008. In the northern Bay of Bengal, the NO 3 trend shows significant seasonality. A zonal SST gradient-based index (upwelling index (UI)) is adopted to identify the upwelling zones, results are presented for the prominent upwelling zones of Somalia and Oman. The UI is used to understand the long-term and decadal variation of Somalia and Oman upwelling intensity with the Indian summer monsoon MSLP, surface wind and rainfall variations. Results suggest that Oman upwelling intensity is highly correlated with the monsoon heat low over the northwest India and Pakistan and Indian summer monsoon rainfall over the core region. However, MSLP over the Indian subcontinent and rainfall over the west coast of India is correlated with the Somalia upwelling intensity. Here, we show that surface wind over the central Arabian Sea (monsoon trough) region are correlated with the intensity of UI of Oman (Somalia). The decadal study provides compelling evidence that the relationship between MSLP, near surface wind, upwelling and ISMR weakens over time in Somalia coast but in the Oman coast this relationship strengthens with recent decades. • Long-term and decadal trends of SST, chlorophyll-a and NO 3 are investigated over the Indian Ocean. • Significant warming and decline of chlorophyll-a is depicted in the western and North Indian Ocean. • Recovery of upwelling zones in the western Indian Ocean is evident in the recent decade (2009-2018). • Strong correlation between the Oman upwelling intensity and Indian summer monsoon rainfall is found in the recent decades.

Impact of interventions on the incidence of natural focal diseases during the outbreak of COVID-19 in Jiangsu Province, China

BackgroundDuring the period of the coronavirus disease 2019 (COVID-19) outbreak, strong intervention measures, such as lockdown, travel restriction, and suspension of work and production, may have curbed the spread of other infectious diseases, including natural focal diseases. In this study, we aimed to study the impact of COVID-19 prevention and control measures on the reported incidence of natural focal diseases (brucellosis, malaria, hemorrhagic fever with renal syndrome [HFRS], dengue, severe fever with thrombocytopenia syndrome [SFTS], rabies, tsutsugamushi and Japanese encephalitis [JE]).MethodsThe data on daily COVID-19 confirmed cases and natural focal disease cases were collected from Jiangsu Provincial Center for Disease Control and Prevention (Jiangsu Provincial CDC). We described and compared the difference between the incidence in 2020 and the incidence in 2015–2019 in four aspects: trend in reported incidence, age, sex, and urban and rural distribution. An autoregressive integrated moving average (ARIMA) (p, d, q) × (P, D, Q)s model was adopted for natural focal diseases, malaria and severe fever with thrombocytopenia syndrome (SFTS), and an ARIMA (p, d, q) model was adopted for dengue. Nonparametric tests were used to compare the reported and the predicted incidence in 2020, the incidence in 2020 and the previous 4 years, and the difference between the duration from illness onset date to diagnosed date (DID) in 2020 and in the previous 4 years. The determination coefficient (R2) was used to evaluate the goodness of fit of the model simulation.ResultsNatural focal diseases in Jiangsu Province showed a long-term seasonal trend. The reported incidence of natural focal diseases, malaria and dengue in 2020 was lower than the predicted incidence, and the difference was statistically significant (P < 0.05). The reported incidence of brucellosis in July, August, October and November 2020, and SFTS in May to November 2020 was higher than that in the same period in the previous 4 years (P < 0.05). The reported incidence of malaria in April to December 2020, HFRS in March, May and December 2020, and dengue in July to November 2020 was lower than that in the same period in the previous 4 years (P < 0.05). In males, the reported incidence of malaria in 2020 was lower than that in the previous 4 years, and the reported incidence of dengue in 2020 was lower than that in 2017–2019. The reported incidence of malaria in the 20–60-year age group was lower than that in the previous 4 years; the reported incidence of dengue in the 40–60-year age group was lower than that in 2016–2018. The reported cases of malaria in both urban and rural areas were lower than in the previous 4 years. The DID of brucellosis and SFTS in 2020 was shorter than that in 2015–2018; the DID of tsutsugamushi in 2020 was shorter than that in the previous 4 years.ConclusionsInterventions for COVID-19 may help control the epidemics of natural focal diseases in Jiangsu Province. The reported incidence of natural focal diseases, especially malaria and dengue, decreased during the outbreak of COVID-19 in 2020. COVID-19 prevention and control measures had the greatest impact on the reported incidence of natural focal diseases in males and people in the 20–60-year age group.Graphical

Examining the characteristics of planetary boundary layer height and its relationship with atmospheric parameters over Indian sub-continent

Planetary boundary layer plays a critical role in the monsoon circulation studies at regional scales through exchange of land surface fluxes (heat and moisture) with atmosphere. The objective of the present study is to identify the spatial variability of long-term seasonal trends of planetary boundary layer height (PBLH) over Indian subcontinent and its association with atmospheri parameters. Monthly atmospheric boundary layer height data obtained from European centre for medium range weather forecast ERA-5 reanalysis has been used for the study during 1980–2018. Statistically robust non-parametric Mann Kendall test is used to investigate the significance of trend at 95% confidence interval. From the results it has been observed that decreasing trend for PBLH is noticed during pre-monsoon and monsoon seasons over Indian region. PBLH over central and north-west India is deeper (1600–1800 m) during pre-monsoon season whereas PBLH is shallow during other seasons. Seasonal variation of PBLH shows a strong negative association with the relative humidity (r more than −0.8) whereas it shows strong positive association with surface temperature (r > 0.7) and surface zonal winds (r > 0.5) over Indian subcontinent. Evaporative fraction which acts as a dominant controlling factor for the variation in PBLH is positively associated (r > 0.7) with the PBLH during monsoon season. Decreasing trend of PBLH during monsoon season may be attributed to the decrease in latent heat flux and increase in relative humidity that results in entrap of moisture at lower levels and may enhance the formation of extreme events. Inter annual variability of PBLH over Indian subcontinent demonstrates in-phase relationship with the deficit and excess monsoon years. Further to this, PBLH is found to be strongly negatively correlated with PM2.5 (r more than −0.5) during pre-monsoon and monsoon seasons suggesting an opposite phase relationship between the two parameters.

Long-term trends in rainfall and temperature using high-resolution climate datasets in East Africa

Detecting changes in climate is a prerequisite for a better understanding of the climate and developing adaptation and mitigation measures at a regional and local scale. In this study long-term trends in rainfall and maximum and minimum temperature (T-max and T-min) were analysed on seasonal and annual time scales for East Africa. High resolution gridded rainfall (1981–2016) and temperature (1979–2010) data from international databases like the Climate Hazards Group are used. Long-term seasonal trend analysis shows a non-significant (except for small areas), decreasing (increasing) trend in rainfall in eastern (western) parts of Ethiopia and Kenya and a decreasing trend in large parts of Tanzania during the long rainy season. On the other hand, a non-significant increasing trend in large parts of the region is observed during the short rain season. With regard to annual trends, results largely confirm seasonal analyses: only a few significant trends in rainfall, but significant increasing trends in T-max (up to 1.9 °C) and T-min (up to 1.2 °C) for virtually the whole region. Our results demonstrate the need and added value of analysing climate trends based on data with high spatial resolution allowing sustainable adaptation measures at local scales.

Analyzing the uncertainty of ensemble-based gridded observations in land surface simulations and drought assessment

Hydrologic modeling is one of the primary tools utilized for drought monitoring and drought early warning systems. Several sources of uncertainty in hydrologic modeling have been addressed in the literature. However, few studies have assessed the uncertainty of gridded observation datasets from a drought monitoring perspective. This study provides a hydrologic modeling oriented analysis of the gridded observation data uncertainties over the Pacific Northwest (PNW) and its implications on drought assessment. We utilized a recently developed 100-member ensemble-based observed forcing data to simulate hydrologic fluxes at 1/8° spatial resolution using Variable Infiltration Capacity (VIC) model, and compared the results with a deterministic observation. Meteorological and hydrological droughts are studied at multiple timescales over the basin, and seasonal long-term trends and variations of drought extent is investigated for each case. Results reveal large uncertainty of observed datasets at monthly timescale, with systematic differences for temperature records, mainly due to different lapse rates. The uncertainty eventuates in large disparities of drought characteristics. In general, an increasing trend is found for winter drought extent across the PNW. Furthermore, a ∼3% decrease per decade is detected for snow water equivalent (SWE) over the PNW, with the region being more susceptible to SWE variations of the northern Rockies than the western Cascades. The agricultural areas of southern Idaho demonstrate decreasing trend of natural soil moisture as a result of precipitation decline, which implies higher appeal for anthropogenic water storage and irrigation systems.

Stormwater Runoff Characteristics and Effective Management of Nonpoint Source Pollutants from a Highland Agricultural Region in the Lake Soyang Watershed

The dense highland field area in the upstream region of the Lake Soyang watershed is subject to excessive soil erosion during the wet season. In this study, stormwater runoff from the Lake Soyang watershed was monitored during four rainfall events at 10 locations throughout 2016. The maximum SS concentration at Naedongcheon, which is located in the upper part of the Soyang River, reached 4598 mg/L. The event mean concentration (EMC) of SS loads in Naedongcheon ranged from 82.2 mg/L to 926.3 mg/L. We found that, although the first flush events were usually concentrated in highly paved urban areas, a first flush occurred in the agricultural area of the dense highland field region. The first flush phenomenon was identified by a dimensionless cumulative runoff mass and volume curve (M(V) curve), and the intensity of the first flush was analyzed by the coefficient of the nonlinear regression model and the FF30 and FF25 values (the fraction of pollution load transported by the first 30% and 25% of runoff, respectively). Nonlinear regression models using the power function were applied to fit the M(V) curve, the FF30 values were inversely proportional to the coefficient a of the regression model. A long-term seasonal trend decomposition for monthly turbidity and precipitation was performed for the Lake Soyang. Long-term turbidity trend was approximately coincident with the trend in long-term precipitation. In addition, the present status of the best management practices (BMPs) in the upper part of the Soyang River basin was investigated, and a survey of the management and operation of the BMPs was conducted for selected farmers.

Short-term effects of ambient air pollutants on asthma-related emergency department visits in Indianapolis, Indiana, 2007–2011

Objective: We estimate the short-term associations between daily changes in ambient air pollutants and daily asthma-related emergency department (ED) visits in Indianapolis, IN. Methods: We identified asthma-related ED visits among Indianapolis residents aged ≥5 years. We used Poisson regression in a time-series framework to estimate the increased risk for asthma-related ED visits from exposure to ambient SO2, PM2.5 and ozone during the warm season (April–September) and SO2 and PM2.5 during the cold (October–March) season, from 2007 to 2011. Our models controlled for measured confounders, including weather and respiratory infections, as well as unmeasured confounders using a natural cubic spline to account for long-term seasonal trends. Results: During 2007–2011 in Indianapolis, 165 056 asthma-related ED visits occurred. We found statistically significant positive associations (p < 0.05) between ambient air pollutants and ED visits during the warm season for persons aged 5–44 years. Interquartile range increases in daily ozone concentrations with same day, 2-day lagged, and 3-day moving average were associated with increased risks for ED visits of 3.2% (95% CI: 0.2%, 6.3%), 4.4% (0.1%, 8.9%) and 4.8% (0.2%, 9.6%), respectively. Interquartile range increases in 3-day moving averages for SO2 were associated with an increased risk of 3.3% (95% CI: 0.2%, 6.5%). We identified statistically significant associations (p < 0.05) between increased SO2 and PM2.5 levels and decreased ED visits among some age groups, primarily during the cold season, and no significant positive associations between changes in PM2.5 concentration and asthma-related ED visits. Conclusions: During the warm season, increases in ozone and SO2 concentrations were associated with increased asthma morbidity in children and young adults in Indianapolis. These results will enable reliable estimation of the health impacts of increases in these pollutants on asthma-related ED visits in Indianapolis and similar communities.

Long-term seasonal trends of nitrogen, phosphorus, and suspended sediment load from the non-tidal Susquehanna River Basin to Chesapeake Bay

Reduction of nitrogen (N), phosphorus (P), and suspended sediment (SS) load has been a principal focus of Chesapeake Bay Watershed management for decades. To evaluate the progress of management actions in the Bay's largest tributary, the Susquehanna River, we analyzed the long-term seasonal trends of flow-normalized N, P, and SS load over the last two to three decades, both above and below the Lower Susquehanna River Reservoir System. Our results indicate that annual and decadal-scale trends of nutrient and sediment load generally followed similar patterns in all four seasons, implying that changes in watershed function and land use had similar impacts on nutrient and sediment load at all times of the year. Above the reservoir system, the combined loads from the Marietta and Conestoga Stations indicate general trends of N, P, and SS reduction in the Susquehanna River Basin, which can most likely be attributed to a suite of management actions on point, agricultural, and stormwater sources. In contrast, upward trends of SS and particulate-associated P and N were generally observed below the Conowingo Reservoir since the mid-1990s. Our analyses suggest that (1) the reservoirs' capacity to trap these materials has been diminishing over the past two to three decades, and especially so for SS and P since the mid-1990s, and that (2) the Conowingo Reservoir has already neared its sediment storage capacity. These changes in reservoir performance will pose significant new kinds of challenges to attainment of total maximum daily load goals for the Susquehanna River Basin, and particularly if also accompanied by increases in storm frequency and intensity due to climate change. Accordingly, the reservoir issue may need to be factored into the proper establishment of regulatory load requirements and the development of watershed implementation plans.

Strategies to Enhance the Interpretation of Single-Particle Ambient Aerosol Data

New instruments are beginning to reveal the chemical complexity of atmospheric aerosol particles. Exploitation of the plethora of information being made accessible through aerosol particle spectrometry and other techniques requires new strategies for data interpretation. This paper demonstrates and evaluates several analysis methods used to exploit this single-particle high-time-resolution data. In the first part of this study, Standard Reference Material (SRM) particulate matter samples were analyzed by an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) in order to evaluate the use of a modified, logarithm based, method of clustering mass spectra using the Adaptive Resonance Theory (ART-2a) algorithm. In the second part of this study, data obtained from the ATOFMS during the four seasons of 2007 were interpreted using a variety of approaches so as to elucidate the nature and sources of particles influencing the great lakes region of North America. This dataset is believed to represent the longest time-span of single-particle data ever analyzed in a study of this nature. These mass spectra were clustered into 21 different particle types using the supervised log-transformed ART-2a algorithm. Both long-term seasonal trends and high-time-resolution temporal patterns of particle type concentrations were examined. Source identification was supported by comparison with known source samples. Potential source contribution functions were used to identify source regions. This paper describes and evaluates these approaches to data interpretation using examples from the ambient air study to illustrate the methodology and highlight the findings. Furthermore, these ambient examples demonstrate how the application of these strategies enhances the interpretation of single-particle ambient aerosol data. Copyright 2012 American Association for Aerosol Research

A Quasi-Global Evaluation System for Satellite-Based Surface Soil Moisture Retrievals

A recently developed data assimilation technique offers the potential to greatly expand the geographic domain over which remotely sensed surface soil moisture retrievals can be evaluated by effectively substituting (relatively plentiful) rain-gauge observations for (less commonly available) ground-based soil moisture measurements. The technique is based on calculating the Pearson correlation coefficient (Rvalue) between rainfall errors and Kalman filter analysis increments realized during the assimilation of a remotely sensed soil moisture product into the antecedent precipitation index (API). Here, the existing Rvalue approach is modified by reformulating it to run on an anomaly basis where long-term seasonal trends are explicitly removed and by calculating API analysis increments using a Rauch-Tung-Striebel smoother instead of a Kalman filter. This reformulated approach is then applied to a number of Advanced Microwave Scanning Radiometer soil moisture products acquired within three heavily instrumented watershed sites in the southern U.S. Rvalue -based evaluations of soil moisture products within these sites are verified based on comparisons with available ground-based soil moisture measurements. Results demonstrate that, without access to ground-based soil moisture measurements, the Rvalue methodology can accurately mimic anomaly correlation coefficients calculated between remotely sensed soil moisture products and soil moisture observations obtained from dense ground-based networks. Sensitivity results also indicate that the predictive skill of the Rvalue metric is enhanced by both proposed modifications to its methodology. Finally, Rvalue calculations are expanded to a quasi-global (50? S-50? N) domain using rainfall measurements derived from the Tropical Rainfall Measurement Mission Precipitation Analysis. Spatial patterns in calculated Rvalue fields are compared to regions of strong land-atmosphere coupling and used to refine expectations concerning the global distribution of land areas in which remotely sensed surface soil moisture retrievals will contribute to atmospheric forecasting applications.

Pediatric patient asthma-related emergency department visits and admissions in Washington, DC, from 2001–2004, and associations with air quality, socio-economic status and age group

BackgroundThe District of Columbia (DC) Department of Health, under a grant from the US Centers for Disease Control and Prevention, established an Environmental Public Health Tracking Program. As part of this program, the goals of this contextual pilot study are to quantify short-term associations between daily pediatric emergency department (ED) visits and admissions for asthma exacerbations with ozone and particulate concentrations, and broader associations with socio-economic status and age group.MethodsData included daily counts of de-identified asthma-related pediatric ED visits for DC residents and daily ozone and particulate concentrations during 2001–2004. Daily temperature, mold, and pollen measurements were also obtained. After a cubic spline was applied to control for long-term seasonal trends in the ED data, a Poisson regression analysis was applied to the time series of daily counts for selected age groups.ResultsAssociations between pediatric asthma ED visits and outdoor ozone concentrations were significant and strongest for the 5–12 year-old age group, for which a 0.01-ppm increase in ozone concentration indicated a mean 3.2% increase in daily ED visits and a mean 8.3% increase in daily ED admissions. However, the 1–4 yr old age group had the highest rate of asthma-related ED visits. For 1–17 yr olds, the rates of both asthma-related ED visits and admissions increased logarithmically with the percentage of children living below the poverty threshold, slowing when this percentage exceeded 30%.ConclusionSignificant associations were found between ozone concentrations and asthma-related ED visits, especially for 5–12 year olds. The result that the most significant ozone associations were not seen in the age group (1–4 yrs) with the highest rate of asthma-related ED visits may be related to the clinical difficulty in accurately diagnosing asthma among this age group. We observed real increases in relative risk of asthma ED visits for children living in higher poverty zip codes versus other zip codes, as well as similar logarithmic relationships for visits and admissions, which implies ED over-utilization may not be a factor. These results could suggest designs for future epidemiological studies that include more information on individual exposures and other risk factors.

The impact of water resources development projects on water vapor pressure trends in a semi-arid region, Turkey

The aim of this study was to investigate long-term seasonal trends and decadal change patterns of monthly mean water vapor pressure (WVP) observation series at 16 meteorological stations scattered point-wisely over the Southeastern Anatolian Project (GAP) area in Turkey, where large-scale soil and water development projects have been put into practice since the 1970s. The record length of WVP observation series of each station varied between 31- and 41-years between 1962 and 2002. The monthly mean WVP observation series of each station was rearranged on seasonal basis. Sequential Mann–Kendall trend test, Sen’s slope estimator, and Spearman’s rank–order correlation tests were employed for detection of likely trends, and Kruskall–Wallis test was used to detect decadal variations in WVP series of each observation station. A possible area of representation for each meteorological station was determined by using the Thiessen polygons technique in a geographical information systems media. It was found that 15 seasonal WVP series have a positive trend covering 97% of the GAP area in the summer season; although one WVP series has a negative trend direction. However, in the spring season, 33% of the area had a positive trend, and a negative trend did not appear in any stations. WVP records in the winter season showed an increasing trend over 19% of the GAP area, whereas a decreasing trend prevailed in 9% of the area. The study results led us to conclude that the substantial increase of WVP observations in summer season could be attributed to both the shift from rain-fed agriculture to irrigated agriculture being made increasingly spacious year by year and building large water reservoirs in the GAP located in a semi-arid region. The results also indirectly suggested that the historical trends in the WVP parameters might be related to global climate change phenomenon.

Nitrogen and silicon limitation of phytoplankton communities across an urban estuary: The East River-Long Island Sound system

To understand how nutrient loading may impact phytoplankton community growth, structure, and photosynthetic efficiency in Long Island Sound (LIS), nutrient enrichment (N, P, or Si) experiments were conducted at stations along the longitudinal gradient of the East River-Long Island Sound system during high and low river flow conditions (spring and summer). During summer, East River (ER) phytoplankton showed no response to N, P, or Si additions. In contrast, N enrichment significantly increased growth rates of all algal size classes (pico- (<3 μm), nano- (3–20 μm) and microphytoplankton (>20 μm)) and most major groups (dinoflagellates, diatoms) beyond control treatments in all regions of LIS (western, WLIS, central, CLIS and eastern, ELIS). Nitrogen enrichment also increased particulate organic carbon production and the photosynthetic efficiency of the phytoplankton community. During spring, ER phytoplankton remained nutrient replete, while larger phytoplankton (nano- and microphytoplankton; diatoms, dinoflagellates) within WLIS and CLIS algal communities were stimulated by N and/or Si additions (1.5- to 7-fold increased growth rates). An absence of response in ELIS phytoplankton following nutrient enrichment during spring together with elevated dissolved inorganic nutrients concentrations and river discharge rates suggests that seasonal variation in river flow can impact the degree to which ELIS phytoplankton are nutrient-limited. A 14-year record of nutrient concentrations and ratios in LIS suggested that our experimental results were representative of long-term seasonal trends, with N-limitation most likely to occur during the spring, summer, and fall in CLIS, during summer and fall in ELIS, and during late spring and summer in WLIS. The existence of low silicate levels relative to inorganic nitrogen in WLIS during spring months suggested that anthropogenic nutrient loading in this region may promote the seasonal Si-limitation of diatoms at this time.

Contribution to F2 layer ionization due to the solar wind

It is now generally believed that, with the exception of auroral and higher latitudes, the F2 layer of the ionosphere is created solely by solar electromagnetic wave radiations in the UV/EUV range. This concept, however, does not appear to offer a logical explanation for the observed equinoctial maxima in planetary F2 layer ion density. It has also not been possible to produce a global-scale model of the critical frequency of the F2 layer covering a solar cycle on the basis of a single UV/EUV source. However, similar equinoctial maxima in the long-term averaged, seasonal trends of such diverse geophysical phenomena as geomagnetic activity, auroral activity, ring current intensity, planetary F2 layer ion density and the neutral thermospheric gas density are also found. The solar wind is now generally accepted to be the cause of geomagnetic activity, auroral activity and particle intensity variations within the radiation belts. Quantitative analysis of the long-term seasonal trends of these phenomena presented in this paper suggest that the solar wind may also be responsible for contributing part of the energy required for the production of the F2 layer ionization. Analysis shows that, while about 25% of the planetary ionization of the F2 layer during July may be caused by energy brought in by the solar wind, the yearly average contribution could be as high as 30% of the UV/EUV contribution, with the contribution in the equinoxes being nearly 38%. Since detailed understanding of the precise mechanism of solar wind entry into geospace is still lacking, no mechanism is suggested to show how solar wind energy is transported to the F2 layer (including low and equatorial latitudes). Magnetospheric electric fields, precipitation of energetic neutrals produced through charge exchange reactions with ions in the ring current and radiation belt particles, Joule heating, etc., may all be involved, but the energy for all such processes would still come ultimately from the solar wind. High quality F2 layer critical frequency data from all over the globe have now been available for more than half a century. Once the possibility of the impact of solar wind energy on the F2 layer ion density is recognized and established in precise quantitative terms, such a connection could become a valuable resource for advancing our understanding of solar-terrestrial relations.

Basis of an alternative method of utilizing low-resolution ovary-weight data for the assessment of seasonal spawning trends of the batch-spawning pilchardSardinops ocellatusin the northern Benguela system

The basis of a method for utilizing low-resolution ovary-weight data for the assessment of long-term seasonal trends in the spawning pattern of batch-spawning species is presented. In such species, assessment of changing trends in spawning from long-term catch data may present unique problems if fish with hydrated oocytes are seldom identified in the routine sampling of catches. A prerequisite for the method is to determine the interrelationship between ovary weight, the stages of oocyte development and fish size. For pilchard Sardinops ocellatus, the relationship between ovary weight in g (Y), oocyte volume in mm3 (X 1) and fish length in cm (X 2) was log Y = −1,97 + 0,52 log X 1 + 2,66 log X 2. The relationship was used to determine ovary-weight boundaries for a selected stage of oocyte development close to hydration for all length classes. These boundaries were then applied to low-resolution catch data from about 10 000 females collected between June 1972 and October 1974 to show the monthly percentages of fish close to spawning. For a species spawning batches at short intervals over a long period, the analysis revealed the beginning and end of spawning, as well as peaks during the spawning season, more clearly than did gonosomatic indices.