Climatological Period Research Articles

Climate and extrema of ocean waves in the East China Sea

Wave climate plays an important role in the air-sea interaction over marginal seas. Extreme wave height provides fundamental information for various ocean engineering practices, such as hazard mitigation, coastal structure design, and risk assessment. In this paper, we implement a third generation wave model and conduct a high-resolution wave hindcast over the East China Sea to reconstruct a 15-year wave field from 1988 to 2002 for derivation of monthly mean wave parameters and analysis of extreme wave conditions. The numerical results of the wave field are validated through comparison with satellite altimetry measurements, low-resolution reanalysis, and the ocean wave buoy record. The monthly averaged wave height and wave period show seasonal variation and refined spatial patterns of surface waves in the East China Sea. The climatological significant wave height and mean wave period decrease from the open ocean in the southeast toward the continental area in the northwest, with the pattern generally following the bathymetry. Extreme analysis on the significant wave height at the buoy station indicates the hindcast data underestimate the extreme values relative to the observations. The spatial pattern of extreme wave height shows single peak emerges at the southwest of Ryukyu Island although a wind forcing with multi-core structure at the extreme is applied.

Classification of Croatian winegrowing regions based on bioclimatic indices

The aim of this work was to classifie vine growing regions of Croatia using bioclimatic indices. For the analysis of climatic conditions, linear trends of bioclimatic indices were determined using meteorological observations for all avaliable climatological stations located in vine growing regions of Croatia. Analysis were performed for two different climatological periods: 1961-1990 and 1988-2017. Four commonly used bioclimatic indices were determined: the Winkler index, the Huglin index, Cool night index and Growing season average temperature.

Attribution of extreme precipitation in the lower reaches of the Yangtze River during May 2016

May 2016 was the third wettest May on record since 1961 over central eastern China based on station observations, with total monthly rainfall 40% more than the climatological mean for 1961–2013. Accompanying disasters such as waterlogging, landslides and debris flow struck part of the lower reaches of the Yangtze River. Causal influence of anthropogenic forcings on this event is investigated using the newly updated Met Office Hadley Centre system for attribution of extreme weather and climate events. Results indicate that there is a significant increase in May 2016 rainfall in model simulations relative to the climatological period, but this increase is largely attributable to natural variability. El Niño years have been found to be correlated with extreme rainfall in the Yangtze River region in previous studies—the strong El Niño of 2015–2016 may account for the extreme precipitation event in 2016. However, on smaller spatial scales we find that anthropogenic forcing has likely played a role in increasing the risk of extreme rainfall to the north of the Yangtze and decreasing it to the south.

СТІЙКІСТЬ ЦЕНТРІВ ВІДКЛАДЕНЬ ОЖЕЛЕДІ КАТЕГОРІЇ НЯ В УКРАЇНІ У ДРУГІЙ ПОЛОВИНІ ХХСТ.-ПОЧАТКУ ХХІСТ.

The article identified and studied meteorological station at which the maximum observed incidence of AEs category ice deposits on the territory of Ukraine for months and some cold months of the warm period of the year for a number of periods: climatological standard norms 1961-1990 biennium., And 1991-2000, 2001- 2010 and 2011-2015. It was established that in all regions of Ukraine during the period are meteorological stations with the highest number of cases of ice deposits category AEs that are repeated in most of the studied months. This indicates a resistance centers of deposits in time and space and show no chance of occurrence of these deposits. In the months warm period was not always meteorological stations of the maximum number of cases of ice deposits category of AEs consistent with other researched for months. In most areas studied during 4 periods set a number of meteorological stations with the maximum number of cases of ice deposits category AEs that are repeated from one period to another. The ferry is such that were recorded only in one of those periods and is not present in others. The study produced the following results: - For all 4 study period in most regions of Ukraine is a meteorological station on which there is the highest incidence of AEs category deposition of ice, that they form centers of deposits. - Most of the study period for the vast number of areas often one and the same center ice deposits category AEs observed in the months of cold period of the year - January, February, November, December, and sometimes March. However, in some areas they may be repeated in the months warm season (April to October). - The standard climatological period 1961-1990 standards. Most stable center ice deposits in the category of AEs observed areas: Rivne, Ivano-Frankivsk, Chernivtsi, Zakarpattia, Poltava, Zaporozhye, Lugansk, Donetsk, Mykolaiv, Kherson and Crimea. In Kyiv and Kirovohrad regions revealed the instability of center ice deposits category AEs in this period, considering all months of cold season and some warm months. - In 2000-2001 In most regions established centers category AEs ice deposits found that the stability of its positioning from month to month, namely Chernihiv, Sumy, Zakarpattia, Rivne, Lviv, Khmelnytsky, Poltava, Kharkiv, Luhansk, Kirovohrad, Dnipropetrovsk, Donetsk, Odessa, Zaporozhye and Kherson. With that, the most stable ice deposits were centers category of AEs of areas: Zakarpattia, Ternopil, Luhansk, Donetsk and Zaporizhia. For areas such as Ivano-Frankivsk, Ternopil, Chernivtsi, Zhytomyr, Kyiv, Vinnitsa, Mykolayiv and Crimea, sustainable centers of deposits is not established, though some of them, Zhytomyr, Kyiv, Mykolaiv, Kherson and Crimea establishes separate centers of deposits in which there are certain prerequisites for their probable sustainability. - 2001-2010. Resilience center ice deposits category of AEs was found in the areas of: Zakarpattya, Ivano-Frankivsk, Chernivtsi, Chernihiv, Poltava, Kharkiv, Luhansk, Donetsk, Dnipropetrovsk, Odessa, Zaporozhye. The most resistant were centers of such deposits in the areas: Zakarpattia, Ivano-Frankivsk, Poltava, Lugansk. Volatility center ice deposits category of AEs found in most regions: Volyn, Rivne, Sumy, Zhytomyr, Kyiv, Lviv, Khmelnytsky, Ternopil, Cherkasy, Vinnytsia, Kirovohrad, Mykolaiv, Kherson and Crimea. - During 2001-2015. In Zakarpattia, Rivne, Lviv, Ternopil, Ivano-Frankivsk, Luhansk, Kirovohrad, Dnipropetrovsk and Odessa regions were found stable ice deposits Centers category AEs not resistance centers ice deposits category AEs were installed in areas - Chernivtsi , Khmelnytsky, Zhytomyr, Kyiv, Sumy, Poltava, Kharkiv, Cherkassy, Vinnitsa, Donetsk, Zaporizhzhia and Crimea. However, in areas such as Chernivtsi, Poltava, Kharkiv, Poltava, Vinnitsa, Donetsk, Nikolaev was revealed station with the highest number of cases of ice deposits category AEs that further potential to be sustainable centers of deposits. - In general for the studied periods (1961-1990, 1991-2000, 2001-2010, 2011-2015.) Found that plants have the maximum number of cases of ice deposits category of AEs mostly repeated in periods of not less than 2 s of them, particularly including the base period. Some of these stations are even more stability and areavailable in more study period 3, or even all 4 periods: Play, Rivne, Chernivtsi, White Church, Fastow, Poltava, Kropivnitskiy, Volyn, Svitlovodsk, Sinelnikovo, Gift 'yivka, Debaltseve, Lyubashevka Ascania Nova, lower Sirogozy. - It was found that most of the stations with the maximum number of cases of categories AEs ice deposits that often repeated in the entire study period observed in Kharkiv, Vinnytsia, Kirovohrad and Crimea.

Decomposition and modelling of the annual cycle of meteorological variables in the Ukrainian Carpathians

Formulation of the problem. In this paper we consider some structural peculiarities of the seasonal cycle of a number of meteorological variables (air temperature, sum of precipitations, saturation deficit, relative humidity, water vapour pressure, station level and sea level pressure, wind speed) in the Ukrainian Carpathians, with the annual cycle being interpreted as a superposition of six harmonics with the period ranging from 2 months to 1 year. Data and methods. This research is based on the average monthly values of seven meteorological variables in the Ukrainian Carpathians within a standard climatological period of 1961-1990. Implicit frequencies in seasonal fluctuations were revealed and evaluated with the help of harmonic analysis method. Presentation of the main research material. A particular emphasis has been laid on the parameters of the first (annual) and second (semiannual) harmonics. It was found out that, on average, the annual harmonic explains some 87% of the total variance of the variables, while the semiannual harmonic accounts for more than 7%. It is shown that when considering seasonal fluctuations of air temperature, saturation deficit and water vapour pressure annual harmonic will suffice. Analyzing fluctuations of other meteorological variables requires a semiannual harmonic to be taken into account. Higher order harmonics (from third to fifth) are to be taken into consideration when analyzing relative humidity, sum of precipitations, station level pressure, and wind speed. The last harmonic (with a period of 2 months) does not play any significant role at all. It was found out that the seasonal cycle structure of these meteorological variables at mountain weather stations and at foothill ones differ noticeably. For some meteorological variables, namely saturation deficit, air temperature, water vapour pressure and atmospheric pressure, orographic effects that manifest in either delayed or early phase of the annual cycle with relation to altitude, have proved to be statistically significant. Phases of this harmonic are typical of meteorological variables that are directly interdependent, while variables that are inversely interdependent normally fluctuate in antiphase.

Timing of Deglacial AMOC Variability From a High‐Resolution Seawater Cadmium Reconstruction

AbstractA new, high‐resolution record of benthic seawater Cd (Cdw) was generated from a Florida Straits sediment core at 546 m water depth. The record provides additional evidence for Cdw below modern values in this channel during the Younger Dryas and Heinrich Stadial 1—climatological periods associated with ice sheet melt. Lower Cdw values are interpreted as a weakening of the Atlantic Meridional Overturning Circulation (AMOC), reflecting a decreased northward transport of southern sourced higher‐nutrient intermediate waters by the surface return flow of AMOC. Comparison of this new Cdw record with previously published neodymium isotope and δ18O records from the same core shows synchronous transitions, further illustrating the connection between Cdw levels and AMOC strength in the Florida Straits. An increase in Cdw near 16 ka bolsters existing evidence for a resumption of upper branch AMOC strength approximately midway through Heinrich Stadial 1.

Extreme rainfall statistics in the Marche region, Italy

A statistical analysis of the rainfalls is carried out for detecting a possible trend in the observed data. The rainfall dataset refers to the historical series collected in the hydrographic basins of the Marche region. On the one hand, the annual maximum daily, hourly and sub-hourly rainfalls have been analysed, on the other hand Climate Change Indices by Expert Team on Climate Change Detection and Indices (ETCCDI) (R1 mm, Rx1day, R20 mm, R95pTOT, PRCPTOT) have been computed to verify an eventual variation of the frequency of the rainfall regime in the Marche region. The time series, selected in the reference period 1951–2013, have been processed by using the non-parametric Mann–Kendall test. The results confirm that most of the series relating to the annual maximum rainfalls do not exhibit any trend. The absence of trend or the presence of negative trend prevail also in the analysis of the ETCCDI indices. The annual average anomalies of the same indices computed with respect to the climatological reference period 1961–1990 are negative since the mid-1980s, but they appear to show an increasing behaviour in the period 2009–2013.

Changes in Rainfall Characteristics in Wenchi and Saltpond Farming Areas of Ghana

Ghana’s economy heavily relies on agriculture, which is predominantly rainfed across its agro-ecological zones. As a result of this, it is vulnerable to rainfall variability, which tends to have a major impact on the industrial and agricultural production sectors of the country. This study investigates the variations occurring across two major farming areas (Wenchi and Saltpond) within the Transition and Coastal Savannah agro-ecological zones of Ghana respectively. Rainfall variations are studied with rainfall data from 1968-2011 from Ghana Meteorological Agency (GMet). The rainfall analysis is done over two Climatological Periods (CP), 1968-1989 as CP1 and 1990-2011 as CP2. This study uses two climatic extreme indices as well as rainfall amounts and onset over these two agro-ecological zones to investigate the changes that have occurred in rainfall. The study found that in the Coastal agro-ecological zone, CP1 had a decreasing rainfall trend as compared to CP2 with higher variations in Saltpond. In the Transition agro-ecological zone, Wenchi, CP1 also exhibited a decreasing trend as compared to CP2. In addition, onset of rains in Saltpond mostly occurred in May for CP1 but for CP2, it oscillated between April and May. For Wenchi, onset of rains was in March for CP1 and predominantly April for CP2. In going forward, farmers in these agro-ecological zones should be supported to practice effective adaptation and mitigation measures so as to improve their yields in this challenging climate.

On the opposite relation between extreme precipitation over west Amazon and southeastern Brazil: observations and model simulations

ABSTRACTDuring the austral summer of 2014 and 2015, a severe drought occurred in southeastern Brazil at the same time when flooding conditions were registered in the state of Acre in the western Amazonia of Brazil. This study aimed the identification of the atmospheric and oceanic large‐scale characteristics and regional features associated with these conditions, and verification of the Center of Weather Forecasting and Climate Studies/National Institute of Space Research (CPTEC/INPE) atmospheric global circulation model ability in reproducing the observed features. The state of Acre was chosen as a pilot area of the PULSE‐Brazil project – a web platform tool that contains climate, ecological and health data for Brazil. The observational data and model results were analysed for the climatological period of 1981–2010. Correlation analyses between precipitation over west Amazon and atmospheric and oceanic variables indicated the main patterns in both data sets. Extreme wet and dry Januaries over west Amazon were selected to explore the regional and large‐scale associated features. The general results of climate analyses indicated an opposite relation of precipitation between western Amazon and southeastern Brazil, in January, besides the typical precipitation dipole between the south Atlantic convergence zone and southeastern South America. This configuration is related to anomalous humidity flux at low levels and associated anomalous sea level pressure over southeastern South America induced by subsidence. The role of convection anomalies over the Pacific Ocean on South America anomalies is discussed. The wet and dry cases in Acre region display opposite atmospheric anomalies over South America that are linked to wavetrains over the Pacific Ocean, likely related to the opposite conditions of Indonesia‐Pacific tropical convection. Similar patterns of the dry cases were observed during January of 2014 and 2015. The model reproduced some observed atmospheric patterns related to precipitation extremes and the results are discussed in terms of regional and large‐scale climate variability.

ONDAS DE FRIO E ENFERMIDADES RESPIRATÓRIAS: ANÁLISE NA PERSPECTIVA DA VULNERABILIDADE CLIMÁTICA

As repercussões das dinâmicas dos elementos atmosféricos no território são deflagradas, fundamentalmente, pelas formas através das quais o espaço geográfico é produzido pelos grupos sociais. Nesse contexto, o artigo procurou abordar a relação entre o conceito de eventos extremos e vulnerabilidade a enfermidades respiratórias utilizando-se de estudo exploratório sobre ondas de frio em Piracicaba – São Paulo. Para a sua identificação, foram utilizados cinco índices climáticos diferentes aplicados aos dados de temperaturas mínimas, obtidos pelo INMET. As ondas de frio detectadas em cada um dos índices foram correlacionadas (comparativamente) com os dados de internação por doenças respiratórias obtidos no DataSUS, entre os anos de 1998 e 2014. Os resultados indicam a ocorrência de maior número de ondas de frio nos meses de inverno, ocorridas principalmente no período da normal climatológica (1961-1990) quando comparada ao período recente (1991-2014). Entre as técnicas comparadas, observou-se que a quantidade de ondas identificadas é díspar e varia de 72 (CSDI-OMM) a 329 ondas (IPCC) na mesma série histórica. Na análise da vulnerabilidade, foi identificado que a faixa etária mais afetada por enfermidades respiratórias é de 0 a 9 anos e acima de 80 anos, mais da metade do total de internações entre 1998 a 2014 (21.115 internações). De modo geral, os meses representativos do inverno, que havia apresentado maior ocorrência de ondas de frio, também apresentaram maior número de internações, principalmente o mês de julho, com uma média superior a 200 internações. Por fim, os resultados indicam que não é apenas a temperatura (onda de frio) a principal responsável pela deflagração de enfermidades respiratórias. Concluiu-se a necessidade de se abordar os conceitos de eventos extremos e vulnerabilidade para uma análise socioespacial da produção das doenças respiratórias, onde os elementos climáticos consistem em apenas um fator para a deflagração dessas doenças.

Climatic influence on corn sowing date in the Midwestern United States

ABSTRACTThis study investigated the climatic influence on the corn sowing date in the Midwestern United States by comparing the survey data of corn cultivation with meteorological records in nine states for the last 36 years (1979–2014). The results show that the year‐to‐year changes in the sowing date were significantly affected by springtime air temperature and precipitation in the nine states, although large state‐to‐state differences were found in the degree of sowing date–meteorology relationship. We determined that the 36‐year climatological warm period (CWP) with daily mean temperatures ≥10 °C plays an important role in the state‐to‐state differences. For the states with longer CWPs, the influence of air temperature (precipitation) was generally weaker (stronger). This observed counteractive relationship should be considered for crop modelling for more effective assessment of the impact of climate change on agriculture.

Wind-wave hindcast in the Yellow Sea and the Bohai Sea from the year 1988 to 2002

We performed long-term wind-wave hindcast in the Yellow Sea and the Bohai Sea from the year 1988 to 2002, and then analyzed the regional wave climate. Comparisons between model results and satellite data are generally consistent on monthly mean significant wave height. Then we discuss the temporal and spatial characteristics of the climatological monthly mean significant wave heights and mean wave periods. The climatologically spatial patterns are observed as increasing from northwest to southeast and from offshore to deep-water area for both significant wave height and mean wave period, and the patterns are highly related to the wind forcing and local topography. Seasonal variations of wave parameters are also significant. Furthermore, we compute the extreme values of wind and significant wave height using statistical methods. Results reveal the spatial patterns of N-year return significant wave height in the Yellow Sea and the Bohai Sea, and we discuss the relationship between extreme values of significant wave height and wind forcing.

Morphology-based functional groups as effective indicators of phytoplankton dynamics in a tropical cyanobacteria-dominated transitional river–reservoir system

Cyanobacteria dominance is often associated with economic, ecological and health problems. The potential production of toxic compounds calls for frequent monitoring of cyanobacteria and their toxin production in many aquatic systems. Methods to simplify this process and facilitate management responses to sudden environmental changes are needed to improve the capability of risk-assessment. We tested the effectiveness of two different functional approaches (Functional Groups – FG, Reynolds et al., 2002; and Morphology-Based Functional Groups – MBFG, Kruk et al., 2010) as well as single species and taxonomic classifications as the best proxy of spatio-temporal phytoplankton dynamics and dominance of toxic algae in an impacted transitional river–reservoir system in the tropics. The Paraíba do Sul River and Funil Reservoir are located in one of the most heavily impacted regions of Brazil, and the latter system has a history of intense, long-lasting toxic cyanobacteria blooms. Sampling was conducted over the two climatological periods of the region: warm-rainy (October/2011 and January/2012) and cold-dry (July/2011 and May/2012), with stations in the following areas: tributary, reservoir and river (downstream from the dam). Our results showed that the MBFG classification was the most effective approach, i.e., best explained the response of the phytoplankton community to environmental variations. Environmental factors including light, nutrients, water temperature and hydrology increased the occurrence of different MBFGs on both spatial and temporal scales. The lotic areas showed a more diverse composition of MBFGs, including species with high to moderate tolerance to light limitation and flushing conditions (MBFGs I, III, IV, V and VI). In Funil Reservoir, phytoplankton biovolume was dominated by bloom-forming cyanobacteria (MBFGs III and VII) and remained high throughout the study. This dominance was related to the overall eutrophic conditions, low light availability and increased water-column stability of the reservoir. The seasonal dynamics in the reservoir was mainly related to changes in temperature and hydrology. Our results show for the first time that morphology captures efficiently eco-strategies of bloom-forming cyanobacteria and the MBFG approach can be used to predict and monitor the development of cyanobacteria HABs in temporal and spatial scales.

Best Bet Technology Package Development to Improve Sorghum Yields in Ethiopia Using the Decision Support System for Agro-Technology Transfer (DSSAT) Model

Sorghum is grown mainly in the semi-arid areas. In spite of the fact that there was observed high climate variability in the last few decades, rain fed sorghum [Sorghum bicolor (L.) Moench] production is still an important source of food and feed in the semiarid regions of Ethiopia. Although sorghum is realized as crop tolerant to water deficit, compared with other semiarid crops in Ethiopia, climate variability and change has been challenging its production and no intensive crop simulation modeling was done as it was desired. In this study the CERES-Sorghum Model of Decision Support System for Agro-Technology Transfer (DSSAT) has been tested over the north Rift Valley of Ethiopia. We have checked what would be the best combination of management options under research and farmers’ practice conditions for each sites for the historical climatological periods (1980-2010) in which we have found that the model performs well in assimilating the real situation in our sentinel sites in both research and farmers’ management practices. The potential grain yield from the DSSAT model would go up to 2.5T/ha under best scenario rainfall seasons without applying the developed technology package application (which we call it farmer’s condition). The same sorghum variety has a potential yield of 6.2 T/ha if one can apply the recommended best bet technology packages (planting date, planting population, sowing data, fertilizer application rate and time) within the same season. Hereby we can assert that the application of the developed technology packages would make a difference of up to 3.7 T/ha of grain sorghum yield under the same season. Even though applying the technology packages according to the prevailing seasons would significantly matter the expected grain yield, the worst possible grain yield lose would be minimized by applying the best bet technology packages that fits the specific season. Moreover, the selected sentinel sites were few, the result can be extrapolated using the calibrated crop simulation modeling to larger areas to develop strategic plans to improve grain yield of sorghum in Ethiopia.

Оцінка сучасного стану вітрових ресурсів Українських Карпат та їх зміни відносно базового кліматичного періоду

Оцінка сучасного стану вітрових ресурсів Українських Карпат та їх зміни відносно базового кліматичного періоду

Possible Location of the Polar Front Over the Eastern European Plain in the Middle of the 21 Century

The location of the polar front and its possible change in European Russia during a summer season in the middle of the 21 century is investigated based on the results of climate modeling on a regional climate model of Main Geophysical Observatory. The simplest method to identify the location of the polar front on the map using the areas of high temperature gradients is examined. The polar front orientation will become more meridional according to model data in comparison with climatological polar front identifi ed by Khromov in the 20 century. The stability of the polar front during the various climatological periods is revealed. It is possible to expect a shift of the area of largest temperature gradients to the south in the middle of the 21 century on one degree of latitude compared with the last decade of the 20 century

The roles of environmental conditions and geographical distances on the species turnover of the whole phytoplankton and zooplankton communities and their subsets in tropical reservoirs

Understanding the patterns of biological diversity between different regions (beta diversity) and how diversity is generated and maintained is a central goal in ecology. The relative roles of niche differentiation and geographical distances in shaping the phytoplankton and zooplankton structures are not yet fully determined, especially considering the subsets of species that share particular traits. We evaluated whether dissimilarity in phytoplankton and zooplankton assemblages depends on environmental distances and geographical distances on the whole communities and for subsets. We sampled eight hydroelectric reservoirs over a large scale (1500 km) in central Brazil, during three climatological periods. Phytoplankton composition was correlated with niche differentiation; that is, environmental similarity would account for assemblage similarity, due to the high dispersal abilities and low turnover rates of these organisms. For zooplankton, geographical distances were more important, which resulted in a stronger spatial structure with a greater dispersal limitation. For phytoplankton, the Morphologically Based Functional Group formed by diatoms, and for zooplankton, the three major taxonomic groups appeared as spatially structured. Therefore, phytoplankton composition was mostly correlated to niche differentiation and zooplankton to geographical distances; the communities deconstructed into subsets of species with similar traits refined the responses of the community structures.

Projected changes in tropical cyclones over Vietnam and the South China Sea using a 25 km regional climate model perturbed physics ensemble

The regional climate modelling system PRECIS, was run at 25 km horizontal resolution for 150 years (1949–2099) using global driving data from a five member perturbed physics ensemble (based on the coupled global climate model HadCM3). Output from these simulations was used to investigate projected changes in tropical cyclones (TCs) over Vietnam and the South China Sea due to global warming (under SRES scenario A1B). Thirty year climatological mean periods were used to look at projected changes in future (2069–2098) TCs compared to a 1961–1990 baseline. Present day results were compared qualitatively with IBTrACS observations and found to be reasonably realistic. Future projections show a 20–44 % decrease in TC frequency, although the spatial patterns of change differ between the ensemble members, and an increase of 27–53 % in the amount of TC associated precipitation. No statistically significant changes in TC intensity were found, however, the occurrence of more intense TCs (defined as those with a maximum 10 m wind speed >35 m/s) was found to increase by 3–9 %. Projected increases in TC associated precipitation are likely caused by increased evaporation and availability of atmospheric water vapour, due to increased sea surface and atmospheric temperature. The mechanisms behind the projected changes in TC frequency are difficult to link explicitly; changes are most likely due to the combination of increased static stability, increased vertical wind shear and decreased upward motion, which suggest a decrease in the tropical overturning circulation.

The Impact of Time Difference between Satellite Overpass and Ground Observation on Cloud Cover Performance Statistics

Cloud property data sets derived from passive sensors onboard the polar orbiting satellites (such as the NOAA’s Advanced Very High Resolution Radiometer) have global coverage and now span a climatological time period. Synoptic surface observations (SYNOP) are often used to characterize the accuracy of satellite-based cloud cover. Infrequent overpasses of polar orbiting satellites combined with the 3- or 6-h SYNOP frequency lead to collocation time differences of up to 3 h. The associated collocation error degrades the cloud cover performance statistics such as the Hanssen-Kuiper’s discriminant (HK) by up to 45%. Limiting the time difference to 10 min, on the other hand, introduces a sampling error due to a lower number of corresponding satellite and SYNOP observations. This error depends on both the length of the validated time series and the SYNOP frequency. The trade-off between collocation and sampling error call for an optimum collocation time difference. It however depends on cloud cover characteristics and SYNOP frequency, and cannot be generalized. Instead, a method is presented to reconstruct the unbiased (true) HK from HK affected by the collocation differences, which significantly (t-test p < 0.01) improves the validation results.

Factors contributing to uncertainty in Pacific Decadal Oscillation index

AbstractPacific Decadal Oscillation (PDO) index is an important indicator of climate variability. However, large discrepancies are found among real‐time PDO monitoring indices maintained by several operational centers, with larger uncertainty exhibiting prior to 1950s and after late 1990s on seasonal to decadal time scales. Two historical sea surface temperature (SST) data sets are used to investigate causes for the uncertainty: the Extended Reconstructed Sea Surface Temperature version 3b (ERSST 3b) and the Hadley Center Sea Ice and SST data set (HadISST) version 1. It is found that choices of spatial structure of Empirical Orthogonal Function (EOF) vector and SST data set are important sources of uncertainty on seasonal to decadal time scales, while choice of climatological base period only contributes to uncertainty on seasonal time scale. Decadal variation of differences in PDO indices from ERSST and HadISST is associated with systematic differences between the two data sets in the central and the north‐eastern Pacific.