NCEP Reanalysis Research Articles

Realization of global empirical model for mapping zenith wet delays onto precipitable water using NCEP re-analysis data

Realization of global empirical model for mapping zenith wet delays onto precipitable water using NCEP re-analysis data

Retrieval of Layer Averaged Relative Humidity Profiles from MHS Observations over Tropical Region

The present paper deals with the retrieval of the atmospheric layer averaged relative humidity profiles using data from the Microwave Humidity Sounder (MHS) onboard the MetOp satellite. The retrieval has been innovatively performed by firstly retrieving humidity for pairs of thick overlapping layers (TOLs) used subsequently to derive humidity for associated thin isolated layer (TIL). A water vapour dependent (WVD) algorithm has been developed and applied to infer the humidity of TOLs. Thus, the retrieved profiles have been finally compared with standard algorithm (NORM). These algorithms have been developed based on radiative transfer simulations and study of sensitivities of MHS channels on humidity of various types of layers (TOL, TIL). The algorithm has been tested with MHS data and validated using concurrent radiosonde as well as NCEP reanalysis data indicating profile errors of ~15% and ~19%, respectively.

On the Strengthened Relationship between the East Asian Winter Monsoon and Arctic Oscillation: A Comparison of 1950–70 and 1983–2012

In this paper, the authors use NCEP reanalysis and 40-yr ECMWF Re-Analysis (ERA-40) data to document the strengthened relationship between the East Asian winter monsoon (EAWM) and winter Arctic Oscillation (AO) on the interannual time scale with a comparison of 1950–70 and 1983–2012. Their connection was statistically insignificant during 1950–70, whereas it was statistically significant during 1983–2012. The latter significant connection might be attributed to the East Asian jet stream (EAJS) upstream extension: the EAJS signal is relatively confined to the western North Pacific before the 1970s, whereas it extends westward toward East Asia after the 1980s. This upstream extension leads to the rearrangement of eastward-propagating Rossby waves with a much wider horizontal structure, thereby bonding the EAWM and the AO. Furthermore, the authors present observational evidence and model simulations demonstrating that the reduction of autumn Arctic sea ice cover (ASIC) is responsible for the strengthened EAWM–AO relationship after the 1980s by producing the EAJS upstream extension. After the 1980s, a strong anticyclonic anomaly over the polar ocean and anomalous easterly advection over northern Eurasia are generated by the near-surface heating over the Barents–Kara (B–K) Seas caused by the reduction of ASIC. This further induces cold anomalies over northern Eurasia, altering the meridional temperature gradient between the midlatitude and tropical region and consequently leading to westward penetration of the EAJS.

Consistency of Temperature and Precipitation Extremes across Various Global Gridded In Situ and Reanalysis Datasets

Changes in climate extremes are often monitored using global gridded datasets of climate extremes based on in situ observations or reanalysis data. This study assesses the consistency of temperature and precipitation extremes between these datasets. Both the temporal evolution and spatial patterns of annual extremes of daily values are compared across multiple global gridded datasets of in situ observations and reanalyses to make inferences on the robustness of the obtained results. While normalized time series generally compare well, the actual values of annual extremes of daily data differ systematically across the different datasets. This is partly related to different computational approaches when calculating the gridded fields of climate extremes. There is strong agreement between extreme temperatures in the different in situ–based datasets. Larger differences are found for temperature extremes from the reanalyses, particularly during the presatellite era, indicating that reanalyses are most consistent with purely observational-based analyses of changes in climate extremes for the three most recent decades. In terms of both temporal and spatial correlations, the ECMWF reanalyses tend to show greater agreement with the gridded in situ–based datasets than the NCEP reanalyses and Japanese 25-year Reanalysis Project (JRA-25). Extreme precipitation is characterized by higher temporal and spatial variability than extreme temperatures, and there is less agreement between different datasets than for temperature. However, reasonable agreement between the gridded observational precipitation datasets remains. Extreme precipitation patterns and time series from reanalyses show lower agreement but generally still correlate significantly.

Climatology of the stability and humidity terms in the Haines Index to improve the estimate of forest fire risk in the Western Mediterranean Basin (Valencia region, Spain)

The stability and moisture content of the different atmospheric levels are commonly used to assess the risk index in the propagation and evolution of a hypothetical forest fire. The Haines Index (HI) combines these terms to determine the environmental potential for wildfire growth. In this paper the environmental stability and humidity associated with the lower atmospheric layers in the Western Mediterranean Basin are investigated by analysing HI calculations over a 29-year period. The HI climatology can be applied to the study of plume-dominated forest fires. These fires tend to present very erratic propagation behaviour and create highly dangerous situations for fire brigades. Thus the knowledge of the typical index values and the meteorological situations that generate them could be extremely useful for minimizing the fire risk and planning specific fire-fighting activities. In this study we carry out a spatial and temporal analysis of the Index and its terms in the Valencia region on the basis of NCEP/NCAR reanalysis data from 1980 to 2008, obtaining a detailed climatological analysis of the HI in the Valencia region for each variant of elevation, which can be used as a reference tool. Moreover, using NCEP reanalysis maps at 500 and 850 hPa, we also perform a daily synoptic analysis for the studied period which is finally associated to the different values that the Index can show in this area. As a result three dominant synoptic weather situations have been defined in this region: continental, maritime and convective. A direct proportionality has been found between increases in the HI and convective situations.

Effects of climate change on daily minimum and maximum temperatures and cloudiness in the Shikoku region: a statistical downscaling model approach

In this study, we present a detailed analysis of the effect of changes in cloudiness (CLD) between a future period (2071–2099) and the base period (1961–1990) on daily minimum temperature (TMIN) and maximum temperature (TMAX) in the same period for the Shikoku region, Japan. This analysis was performed using climate data obtained with the use of the Statistical DownScaling Model (SDSM). We calibrated the SDSM using the National Center for Environmental Prediction (NCEP) reanalysis dataset for the SDSM input and daily time series of temperature and CLD from 10 surface data points (SDP) in Shikoku. Subsequently, we validated the SDSM outputs, specifically, TMIN, TMAX, and CLD, obtained with the use of the NCEP reanalysis dataset and general circulation model (GCM) data against the SDP. The GCM data used in the validation procedure were those from the Hadley Centre Coupled Model, version 3 (HadCM3) for the Special Report on Emission Scenarios (SRES) A2 and B2 scenarios and from the third generation Coupled Global Climate Model (CGCM3) for the SRES A2 and A1B scenarios. Finally, the validated SDSM was run to study the effect of future changes in CLD on TMIN and TMAX. Our analysis showed that (1) the negative linear fit between changes in TMAX and those in CLD was statistically significant in winter while the relationship between the two changes was not evident in summer, (2) the dependency of future changes in TMAX and TMIN on future changes in CLD were more evident in winter than in other seasons with the present SDSM, (3) the diurnal temperature range (DTR) decreased in the southern part of Shikoku in summer in all the SDSM projections while DTR increased in the northern part of Shikoku in the same season in these projections, (4) the dependencies of changes in DTR on changes in CLD were unclear in summer and winter. Results of the SDSM simulations performed for climate change scenarios such as those from this study contribute to local-scale agricultural and hydrological simulations and development of agricultural and hydrological models.

De-aggregated hazard of freezing rain events

The objective of the work presented here is to improve estimates of atmospheric icing hazards, specifically for radial ice accumulation on electrical transmission lines, by clustering freezing rainstorms into different groups and using de-aggregate statistical analysis. In this paper, freezing rain storms were clustered based on anomaly maps constructed using NCEP reanalysis data of 1000hPa to 500hPa geopotential heights or SLP. The procedure is demonstrated with data from Montreal, as well as a superstation of Montreal, Quebec City, and Ottawa together. The physical meaning of the different clusters was also analyzed and discussed in terms of wind speed, total precipitation or ice accumulation, air mass positions, and compared with Rauber's archetypical patterns.The results presented indicate that the clusters have statistical and physical significance. Clustering based on either SLP or 1000hPa to 500hPa height anomalies produces clusters with different precipitation characteristics which can be explained on a physical basis. Clustering Montreal storms based on 1000hPa to 500hPa height anomalies produced one cluster containing the five worst ice storms that occurred in Montreal during that time period. This cluster was characterized by an expansive zone of 1000hPa to 500hPa height positive anomalies over Montreal that extend far north. It also shows significant SLP anomalies and cold air damming.The de-aggregated hazard analysis is able to demonstrate that the relative contribution of each cluster changes for more extreme events. The de-aggregated analysis produces optimal statistical fits for clusters and introduces robustness in the estimation of the return period over a range threshold. Finally, a small bias is suggested in the single population analysis where the return periods are consistently lower over a range of quantiles and thresholds.

Padrões de circulação em superfície e em 500 hPa na América do Sul e eventos de anomalias positivas de precipitação no estado de Minas Gerais durante o mês de dezembro de 2011

O presente trabalho apresenta uma classificação dos campos de circulação atmosférica em superfície e 500 hPa sobre a América do Sul durante o mês de dezembro, com o intuito de identificar os principais padrões sinóticos que influenciam o tempo na Região Sudeste do Brasil, principalmente no Estado de Minas Gerais (MG). A metodologia utilizada foi a técnica de Análise de Componentes Principais rotacionadas aplicada à série de reanálises do NCEP para o período 1986-2011. O intuito final desta classificação foi determinar os padrões de circulação predominantes durante o mês de dezembro de 2011, que estiveram relacionados com a ocorrência de precipitações anômalas no Estado de MG. Os resultados obtidos para o período 1986-2011 destacam seis padrões de sequências principais (PSP) de circulação em superfície e quatro padrões de altitude que representam 72,8% e 94% dos casos analisados, respectivamente. Em superfície houve três padrões de circulação principais associados com maior probabilidade de ocorrência de chuva sobre o Estado MG; um deles associado com uma frente fria no sul da Região Sudeste (PSP2-Sup), e outros dois (PSP3-Sup e PSP5-Sup) relacionados com uma configuração de bloqueio de tipo "dipolo" no oceano Atlântico determinado por um anticiclone localizado em torno de 50ºW, 45ºS e por uma baixa posicionado ao norte do anticiclone em torno de 25ºS. Em 500 hPa houve dois padrões de circulação associados com a ocorrência de chuva significativa sobre o Estado mineiro que se refletiram nos campos obtidos em superfície; um deles associado ao avanço de um sistema frontal frio (PSP2-500) e o outro relacionado com uma situação de bloqueio de tipo "dipolo" no oceano Atlântico (PSP4-500). As chuvas anômalas registradas durante dezembro de 2011 estiveram associadas diretamente com a atuação dos padrões de circulação PSP3-Sup e PSP4-500, sendo que ambos os modelos estiveram relacionados com a atuação de episódios de Zona de Convergência do Atlântico Sul (ZCAS).

An observational analysis of the oceanic and atmospheric structure of global-scale multi-decadal variability

The aim of the present study was to identify multi-decadal variability (MDV) relative to the current centennial global warming trend in available observation data. The centennial global warming trend was first identified in the global mean surface temperature (STgm) data. The MDV was identified based on three sets of climate variables, including sea surface temperature (SST), ocean temperature from the surface to 700 m, and the NCEP and ERA40 reanalysis datasets, respectively. All variables were detrended and low-pass filtered. Through three independent EOF analyses of the filtered variables, all results consistently showed two dominant modes, with their respective temporal variability resembling the Pacific Decadal Oscillation/Inter-decadal Pacific Oscillation (PDO/IPO) and the Atlantic Multi-decadal Oscillation (AMO). The spatial structure of the PDO-like oscillation is characterized by an ENSO-like structure and hemispheric symmetric features. The structure associated with the AMO-like oscillation exhibits hemispheric asymmetric features with anomalous warm air over Eurasia and warm SST in the Atlantic and Pacific basin north of 10°S, and cold SST over the southern oceans. The Pacific and Atlantic MDV in upper-ocean temperature suggest that they are mutually linked. We also found that the PDO-like and AMO-like oscillations are almost equally important in global-scale MDV by EOF analyses. In the period 1975–2005, the evolution of the two oscillations has given rise to strong temperature trends and has contributed almost half of the STgm warming. Hereon, in the next decade, the two oscillations are expected to slow down the global warming trends.

Wave climate variability of Taiwan waters

Global sea surface wind field data derived from NCEP reanalysis were used in driving a SWAN wave model to reconstruct historical wave records from 1948 to 2008. The reconstructed wave data were compared and verified by the observation of the data buoys of the Central Weather Bureau and the Water Resources Agency, Taiwan, and the National Data Buoy Center/National Oceanic and Atmospheric Administration, United States. Over the past six decades, the wave climate in Taiwan waters has undergone considerable changes. The annual mean significant wave heights have reduced an average of 0.31 cm/year. Winter wave heights have gradually dropped 0.86 cm/year, which are related to the weakening of winter monsoons. Regarding the inter-annual wave climate variation, the influence of El Nino/southern oscillation was substantial; the wave heights increased in La Nina years and decreased in El Nino years. In the past 60 years, extreme wave events have been concentrated in two periods: 1967–1974 and 2000–2008. More severe extreme wave events occurred in the latter compared with the former, and all were induced by typhoons. A clear trend, in which the summer (winter) extreme wave events have increased (decreased) gradually, has been identified. The 1980s was the transition period. After the transition period, the annual occurrence of extreme wave events caused by typhoons exceeded those caused by an intense outbreak of winter cold surges, although the total number of the annual extreme wave events has not changed substantially.

基于统计降尺度模型的太湖流域降水 气温变化预测

利用太湖流域7个国家气象站实测降水、气温数据和NCEP再分析数据，分别建立了太湖流域降水、气温统计降尺度模型；在A2和B2排放情景下应用HadCM3的输出数据，预测太湖流域未来2020s(2010~2039年)、2050s(2040~2069年)和2080s(2070~2099年)三个时期降水、气温变化情况。研究结果表明：A2情景下，未来3个时期太湖流域降水呈先增加后减少趋势，B2情景下，未来3个时期太湖流域降水呈增加趋势；两种气候情景下，未来3个时期太湖流域气温总体呈上升趋势，其中A2情景比B2情景升温趋势更加显著。本文研究成果可为政府相关决策层制定未来太湖流域社会经济发展规划提供科学的依据。 The observed precipitation series and temperature series from seven national weather stations were used to establish the statistical downscaling model with the NCEP reanalysis data in the Taihu basin, respectively. Then, the output data of HadCM3 under A2 and B2 scenarios were inputted to the established automated statistical downscaling model (ASD) to predict the future precipitation and temperature changes during 2020s(2010-2039), 2050s(2040-2069) and 2080s(2070- 2099) periods in the Taihu Basin. The results show that the precipitation will be increased first and then decreased during the three future periods under A2 scenarios. However, under B2 scenarios, the precipitation will be increased during these three periods. For both A2 and B2 scenarios simulated by HadCM3 outputs, the future temperature will also be increased during these three periods, and the increased trend under A2 scenarios is more significant than the trend under B2 scenarios. The research results in this study will be served as a scientific basis for making the future social and economic development plans of the Taihu Basin by the relevant government decision-making.

泾河流域潜在蒸散量的时空变异

潜在蒸散量是水文循环中的重要变量，分析其当前特征并预测未来变化，对于区域干旱和水文特征分析具有重要的参考意义。基于15个气象站点的日数据、NCEP再分析数据以及HadCM3的预测数据，在分析当前潜在蒸散量的基础上，应用统计降尺度方法对泾河流域21世纪的潜在蒸散量进行了预测。结果表明，1961-2005年泾河流域潜在蒸散量年均值为934.6 mm，且存在空间差异，整体由东向西南方向递减；时间变化上呈不显著的上升趋势。21世纪泾河流域潜在蒸散量呈显著的上升趋势，但存在季节差异，夏季增幅较大而冬季增幅较小；空间分布基本保持现有模式，但区域差异增大。潜在蒸散量增加可能加剧泾河流域的干旱状况，需提前采取一定的应对措施。;Potential evapotranspiration (<em>ET</em>₀) is a key variable of hydrological cycle and has important applications to hydrological modeling and crop irrigation scheduling. Under the background of global warming, analyzing the spatiotemporal characteristics of the present and future <em>ET</em>₀ can provide important information for regional water resource management and sustainable agricultural development. To study the impacts of ecological construction and climate change in the past 50 years on the hydrology in the Jinghe watershed, some researches have assessed the changes of <em>ET</em>₀ for the present period; however, almost no study has focused on the potential changes of <em>ET</em>₀. The objective of this study is to project the change of <em>ET</em>₀ during 21^st century on the basis of the current <em>ET</em>₀ analysis and further discuss its impacts on climate in the Jinghe watershed. The data used in this study included daily weather data from 15 meteorological stations, NCEP reanalysis data which reflects the quasi-observed climate condition and GCM grid outputs from HadCM3 under A2 and B2 scenarios. Penman-Monteith (PM) method and statistical downscaling model (SDSM) were used to calculate <em>ET</em>₀ for the present period of 1961-2005 and project <em>ET</em>₀ for the future period of 2011-2099, respectively. The determination coefficient and Nash–Sutcliffe model efficiency coefficient were used to assess the performance of SDSM. The inverse distance weighted interpolation and nonparametric Mann-Kendall test was used to analyze the spatial distribution and temporal change of <em>ET</em>₀, respectively. Results showed that <em>ET</em>₀ calculated by PM formula correlated to the pan evaporation well, which means that the estimated <em>ET</em>₀ is reliable. With annual average of 934.6 mm for the present period, <em>ET</em>₀ had a spatial difference decreasing from the east to the southwestern part of the Jinghe watershed. An insignificant upward trend of annual <em>ET</em>₀ was detected for the present period and an abrupt change occurred in 1977. The monthly <em>ET</em>₀ distributed as a single peak curve with the greatest and smallest value in June and December, respectively. During 21^st century, <em>ET</em>₀ would greatly increase by 1.9 mm/a and 0.9 mm/a under A2 and B2 emission scenarios, respectively. <em>ET</em>₀ appeared to increase dramatically since 2049 and have an upward abrupt change in 2061. Future <em>ET</em>₀ also varied among seasons with the greatest increase in summer and the least in winter. The spatial distribution of future <em>ET</em>₀ was similar to the current period,but the regional difference would increase over time. The aridity index calculated by the ratio of <em>ET</em>₀ to precipitation revealed that the Jinghe watershed would be threatened by more severe drought during 21^st century, and most regions would have semiarid climate at the end of 21^st century though now it is a transition region with semiarid and subhumid climate. The uncertainties in this study are mainly from GCM and downscaling method; however, as the GCM from HadCM3 used in this study has the best performances in simulating Chinese climate and SDSM has good performances in downscaling the present <em>ET</em>₀, the results should be reliable and will be further validated with more GCM data and downscaling methods. The continuous increase in <em>ET</em>₀ and drought would aggravate the water shortage and further influence the ecological construction and regional development in the Jinghe watershed; therefore, some countermeasures should be adapted in advance to minimize the adverse impacts.

Assessment of Onshore Wind Energy Potential Using Regional Atmospheric Modeling System (RAMS) for Thailand

This paper presents an assessment of the onshore wind energy potential in Thailand using the Regional Atmospheric Modeling System (RAMS). A 9km resolution, 1,150km by 1,750km, wind resource map at 120 m elevation above ground level (agl) is produced based on the NCEP reanalysis database for the three year period of 2009-2011. The onshore wind resource map is validated by comparing the modeling results to observed wind data at 100 m agl from the Pollution Control Department (PCD) of Thailand, and at 120 m agl from the National Research Council of Thailand (NRCT). The Mean Square Error (MSE) is computed and is use as the main criterion to evaluate the simulation results. Results showed that, for the study area, the annual mean wind speeds at 120 m agl are in the range of 1.60-5.83 m/s. For its part, the maximum annual mean power density at 120 m agl is approximately 200W/m2 which corresponds to a wind power density of Class 2. Results show that the region has a good wind regime in the mountain areas of western, southern and eastern Thailand. Further assessment is needed to determine if the onshore wind energy resource could be developed and exploited in order to achieve national renewable energy policy targets in Thailand.

温州沿海大风天气特征分析及预报指标探讨

利用温州北麂、洞头站风速资料以及NCEP再分析资料，对温州市沿海发生的大风天气进行了分析．研究发现温州沿海冬半年的大风主要由冷空气引起，初夏大风主要由倒槽和低压引起，夏季大风主要由台风引起。对引起9级以上大风的天气系统进行了分析，发现冷空气大风发生前一天850 hPa存在锋区，35˚N~45˚N间温差为16℃~26℃，地面40˚N~45˚N气压梯度为12~30 hPa；低压大风和气压梯度大的倒槽大风发生前一天850 hpa低槽的底部到达20˚N~25˚N、105˚E附近，槽前有低空急流。 Using wind speed data of Beiji and Dongtou stations in Wenzhou and NCEP reanalysis data, the strong-wind weather off the coast of Wenzhou was analyzed. The study found that Wenzhou coastal winter wind is mainly caused by the cold air; early summer wind is mainly caused by the trough and low pressure; and summer wind is mainly caused by typhoon. The weather system causing more than 9 strength wind was analyzed. The existence of 850 hPa frontal zone, temperature gradient of 16˚C - 26˚C in 35˚N - 45˚N, and pressure gradient of 12 - 30 hPa in the ground 40˚N - 45˚N were found before the day that cold-air strong wind happened. The trough bottom of 850 hPa was in 20˚N - 25˚N, nearby 105˚E before the day that strong wind caused by low pressure and large gradient trough happened, and the jet stream was in front of trough.

A comparison study of three statistical downscaling methods and their model-averaging ensemble for precipitation downscaling in China

This study evaluated the performance of three frequently applied statistical downscaling tools including SDSM, SVM, and LARS-WG, and their model-averaging ensembles under diverse moisture conditions with respect to the capability of reproducing the extremes as well as mean behaviors of precipitation. Daily observed precipitation and NCEP reanalysis data of 30 stations across China were collected for the period 1961–2000, and model parameters were calibrated for each season at individual site with 1961–1990 as the calibration period and 1991–2000 as the validation period. A flexible framework of multi-criteria model averaging was established in which model weights were optimized by the shuffled complex evolution algorithm. Model performance was compared for the optimal objective and nine more specific metrics. Results indicate that different downscaling methods can gain diverse usefulness and weakness in simulating various precipitation characteristics under different circumstances. SDSM showed more adaptability by acquiring better overall performance at a majority of the stations while LARS-WG revealed better accuracy in modeling most of the single metrics, especially extreme indices. SVM provided more usefulness under drier conditions, but it had less skill in capturing temporal patterns. Optimized model averaging, aiming at certain objective functions, can achieve a promising ensemble with increasing model complexity and computational cost. However, the variation of different methods' performances highlighted the tradeoff among different criteria, which compromised the ensemble forecast in terms of single metrics. As the superiority over single models cannot be guaranteed, model averaging technique should be used cautiously in precipitation downscaling.

The role of sea–land air thermal difference, shape of the coastline and sea surface temperature in the nocturnal offshore convection

ABSTRACTNocturnal precipitation cells and lines occur near the coastline in the whole Mediterranean basin in all seasons. The precipitation events are mainly located in areas where coastal mountain ranges and rivers enhance convergence though the interaction of nocturnal mesoscale and local flows (land breeze, katabatic and drainages winds) with prevailing synoptic wind or with other mesoscale and local flows. The methodology used here to study this phenomenon consists of three stages. First, the Tropical Rainfall Measuring Mission (TRMM) radar satellite database is used to detect nocturnal precipitation near the coastline, from 18 to 09 UTC. An event is included in the study if the 3 hours accumulated precipitation detected by TRMM is stationary near the coast, or has moved slightly onshore or offshore, and has lasted no more than six consecutive hours. Second, the NCEP reanalysis database is used to describe the synoptic conditions and to discard precipitation associated with synoptic events (large low pressure areas, dynamic polar fronts, or troughs, for example). In the final step by using the version 3 of the Weather Research Forecast model, we simulate and analyse some of the selected events to determine the role of the land–sea temperature differences, the curvature of the coastline and the sea surface temperature.The simulations confirm that the nocturnal precipitation studied in the Mediterranean basin near the coastline is formed from the interaction between relatively warm and wet sea-air with the cold air mass from drainage winds, as well as from the convergence of several drainage winds offshore. The mechanism is the same that is used to explain nocturnal precipitation in tropical areas.

Coupling of a regional atmospheric model (RegCM3) and a regional oceanic model (FVCOM) over the maritime continent

Climatological high resolution coupled climate model simulations for the maritime continent have been carried out using the regional climate model (RegCM) version 3 and the finite volume coastal ocean model (FVCOM) specifically designed to resolve regions characterized by complex geometry and bathymetry. The RegCM3 boundary forcing is provided by the EMCWF-ERA40 re-analysis. FVCOM is embedded in the Global MITgcm which provides boundary forcing. The domain of the coupled regional model covers the entire South China Sea with its through-flow, the entire Indonesian archipelago with the Indonesian through-flow (ITF) and includes a large region in the western Pacific and eastern Indian oceans. The coupled model is able to provide stable and realistic climatological simulations for a specific decade of atmospheric–oceanic variables without flux correction. The major focus of this work is on oceanic properties. First, the coupled simulation is assessed against ocean-only simulations carried out under two different sets of air–sea heat fluxes. The first set, provided by the MITgcm, is proved to be grossly deficient as the heat fluxes are evaluated by a two-dimensional, zonally averaged atmosphere and the simulated SST have anomalous cold biases. Hence the MITgcm fluxes are discarded. The second set, the NCEP re-analysis heat fluxes, produces a climatological evolution of the SST with an average cold bias of ~−0.8 °C. The coupling eliminates the cold bias and the coupled SST evolution is in excellent agreement with the analogous evolution in the SODA re-analysis data. The detailed comparison of oceanic circulation properties with the International Nusantara Stratification and Transport observations shows that the coupled simulation produces the best estimate of the total ITF transport through the Makassar strait while the transports of three ocean-only simulations are all underestimated. The annual cycle of the transport is also very well reproduced. The coupling also considerably improves the vertical thermal structure of the Makassar cross section in the upper layer affected by the heat fluxes. On the other hand, the coupling is relatively ineffective in improving the precipitation fields even though the coupled simulation captures reasonably well the precipitation annual cycle at three land stations in different latitudes.

Case studies of sprite-producing and non-sprite-producing summer thunderstorms

Three summer thunderstorms in the eastern region of China were analyzed in detail using multiple data, including Doppler radar, lightning location network, TRMM (Tropical Rainfall Measuring Mission), MTSAT (Multi-Function Transport Satellite) images, NCEP (National Centers for Environmental Prediction) Reanalysis, and radiosonde. Two of the three storms were sprite-producing and the other was non-spriteproducing. The two sprite-producing storms occurred on 1–2 August and 27–28 July 2007, producing 16 and one sprite, respectively. The non-sprite-producing storm occurred on 29–30 July 2007. The major objective of the study was to try to find possible differences between sprite-producing and non-sprite producing storms using the multiple datasets. The results showed that the convection in the 1–2 August storm was the strongest compared with the other storms, and it produced the largest number of sprites. Precipitation ice, cloud ice and cloud water content in the convective regions in the 1–2 August storm were larger than in the other two storms, but the opposite was true in the weak convective regions. The storm microphysical properties along lines through parent CG (cloud-to-ground lightning) locations showed no special characteristics related to sprites. The flash rate evolution in the 1–2 August storm provided additional confirmation that major sprite activity coincides with a rapid decrease in the negative CG flash rate. However, the evolution curve of the CG flash rate was erratic in the sprite-producing storm on 27–28 July, which was significantly different from that in the 1–2 August storm. The average positive CG peak current in sprite-producing storms was larger than that in the non-sprite-producing one.

Comparison of different wind products and buoy wind data with seasonality and interannual climate variability in the southern Bay of Biscay (2000–2009)

Ocean surface winds are essential factors in determining oceanographic and atmospheric processes that can affect ocean circulation and wave generation. Accurate surface wind datasets are needed, therefore, to enable the proper analysis of these processes. Wind data from six databases (National Centers for Environmental Prediction reanalysis (NCEP Reanalysis II), European Centre for Medium-Range Weather Forecasts (ECMWF) re-analysis (ERA-Interim), Modern-Era Retrospective-analysis for Research and Applications (MERRA), NCEP Climate Forecast System Reanalysis (CFSR), QuikSCAT and Cross-Calibrated Multi-Platform (CCMP)) were compared with wind measured in situ by four ocean buoys at the southern limit of the Bay of Biscay. The study covered the period 2000–2009 in such a way that the extent of the time series reduced the margin of error and allowed the disaggregation of the wind data using velocity bins and direction sectors. Statistical results confirmed that datasets with finer spatial resolution (lower than 0.5°×0.5°) gave better results, especially in near-shore areas. A more complete analysis was, therefore, carried out using the finer resolution datasets (QuikSCAT, CCMP and CFSR). This comparison showed that all the datasets were less accurate at low wind speeds (<4ms−1) and more accurate at moderate wind speeds. The calculated mean wind speed errors were similar for the three datasets, and the lowest value (1.67ms−1) was from the CCMP dataset. The lowest mean error for wind direction (~37°) was also observed in the CCMP data. The lowest mean wind speed (and direction) bias was obtained from the QuikSCAT data, and the next lowest from the CFSR data. The seasonality for north and east wind components was also determined for the last decade and the results were consistent with forcing for the continental slope current seasonality and winter temperatures or Navidad by wind stress. Correlations between NAO and north and east wind components were low showing that NAO could not be used as a proxy for local wind stress in the southern Bay of Biscay.

Global variation of COSMIC precipitable water over land: Comparisons with ground‐based GPS measurements and NCEP reanalyses

AbstractRadio occultation (RO) observations of precipitable water (PW) from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) are compared with ground‐based Global Positioning System (GPS) PW for 6 years (2007–2012). From comparisons of more than 120,000 collocated samples, differences in PW between RO and GPS exhibit a standard deviation of less than 3 mm with a global correlation of 0.96 to 0.97. The monthly mean RO PW is also compared to the National Centers for Environmental Prediction (NCEP) reanalyses. PWs over land for RO, GPS, and reanalyses are highly correlated in each hemisphere. We also used the RO data to explore the variation of the monthly mean PW in four regions (Tibetan Plateau, central Australia, Amazon Basin, and central Africa) where ground stations are few. This study highlights the characteristics of these PW climatologies, suggesting that the RO data are useful complements to global reanalyses and other data sets.