Climatological Studies Research Articles

Consistency of the single calculus chain for climatological studies using long-term measurements from thessaloniki lidar station

The long term analysis of 15 years of lidar data derived from a Raman lidar at Thessaloniki is presented here. All measurements have been processed with the latest version 4 of the EARLINET Single Calculus Chain algorithm and are compared with the results from the current operational retrieval algorithm. In this paper we investigate the consistency between the EARLINET database and SCC for the case of Thessaloniki and we identify the issues to be considered when switching from current operations to SCC.

Estudo dos ventos na área central da cidade de Juiz de Fora (MG): um ensaio da espacialização de seus fluxos

Ventos são complexos, mutáveis e muito imprevisíveis, podendo trazer inúmeros benefícios ou transtornos à sociedade. No entanto, ainda são poucos os estudos na climatologia brasileira que tem essa variável como elemento central da pesquisa. É partindo deste contexto, e da constatação de que há num clima urbano distintos gradientes barométricos produzidos a partir dos materiais que constituem as cidades (naturais ou antrópicos), que o presente ensaio metodológico traz como objetivo estudar os sentidos/direções possíveis dos ventos em uma área no centro da cidade de Juiz de Fora – MG, considerando os possíveis fatores que viriam a influenciar no fluxo do ar (relevo e altura dos edifícios) e a formação ou não de corredores de ventos. O estudo se deu utilizando de coleta em campo e em laboratório, através do software ArcGIS 10, e chegou-se a conclusões de que a direção dos ventos é variável principalmente conforme a localização do ponto e hora do dia, apresentando constância na velocidade dos mesmos, prevalecendo as de até 3Km na região baixa da cidade (próximo aos 700m) e até 6 Km no ponto da UFJF, que se localiza a uma altitude de 940 metros de altitude; e inconstância no sentido, não havendo direções predominantes.

Unique relationship between tropical rainfall and SST to the north of the Mozambique Channel in boreal winter

ABSTRACTIn this study, we investigate a possible mechanism for the dichotomy in climatology of marine rainfall and sea surface temperature (SST) over a part of the Southwest Indian Ocean (SWIO) during boreal winter (January and February) with state‐of‐the‐art satellite and reanalysis data sets. Rainfall to the north of the Mozambique Channel, bounded 10°–5°S and 40°–50°E, is found to be quite feeble despite being in the warm SST regime of up to 29–29.5 °C. The rainfall intensity is rather found to be highly associated with the atmospheric surface divergence. The vigorous rainfall is associated with the more convergence over the Intertropical Convergence Zone (ITCZ), while the weak rainfall is linked with the divergence to the north of the Mozambique Channel. The surface divergent flow to the north of the Mozambique Channel is associated with a deep southward penetration of the northerly Indian Winter Monsoon (IWM). Corresponding to the surface divergent field, a relatively high sea level pressure (SLP) compared to the SLP in the ITCZ, weak subsidence, and low‐level stratiform clouds are formed to the north of the Mozambique Channel, despite the warm, tropical SST. These atmospheric conditions are most likely conductive to the inhibition of cumulus convection over the region and the unique relationship between rainfall and SST seems peculiar. Our analysis also shows that the rare occurrence of tropical cyclones over the area is attributed to a high‐pressure surge and the associated positive surface vorticity (anti‐cyclonic). This study suggests that the area to the north of the Mozambique Channel is dynamically interesting for climatological studies.

Climatologic studies inside Sandy Glacier at Mount Hood Volcano in Oregon, USA

Previous investigations of climatic conditions of glaciers primarily focused on the glacier’s surface or on the moulin as the entrance to the glacier’s interior. Many glaciers, however, contain far-reaching cave systems inside the ice that have been understood and investigated as drainage systems for meltwater. Until now, there have been no comprehensive climate studies inside a glacier cave. Thus, the climatic conditions, as well as their effects on the glacier, are unknown. The first climatologic investigations inside the cave system of Sandy Glacier on Mt. Hood in Oregon (USA) in June 2015 have shown that both thermic activity of the volcanic subsurface and chimney effects between the glacier snout at the base of the glacier and higher opening of the moulin can cause drastic melting inside the glacier. Those processes lead to considerably stronger melting from the inside than observations at the surface suggest and can cause an unexpected collapse over a distance of several hundred meters. We will present and assess the first measuring results of both the thermic and flow conditions inside Sandy Glacier.

Comprehensive Study of Optical, Physical, Chemical, and Radiative Properties of Total Columnar Atmospheric Aerosols over China: An Overview of Sun–Sky Radiometer Observation Network (SONET) Measurements

AbstractAn overview of Sun–Sky Radiometer Observation Network (SONET) measurements in China is presented. Based on observations at 16 distributed SONET sites in China, atmospheric aerosol parameters are acquired via standardization processes of operational measurement, maintenance, calibration, inversion, and quality control implemented since 2010. A climatology study is performed focusing on total columnar atmospheric aerosol characteristics, including optical (aerosol optical depth, ÅngstrÖm exponent, fine-mode fraction, single-scattering albedo), physical (volume particle size distribution), chemical composition (black carbon; brown carbon; fine-mode scattering component, coarse-mode component; and aerosol water), and radiative properties (aerosol radiative forcing and efficiency). Data analyses show that aerosol optical depth is low in the west but high in the east of China. Aerosol composition also shows significant spatial and temporal variations, leading to noticeable diversities in optical and physical property patterns. In west and north China, aerosols are generally affected by dust particles, while monsoon climate and human activities impose remarkable influences on aerosols in east and south China. Aerosols in China exhibit strong light-scattering capability and result in significant radiative cooling effects.

A Climatological Study of Short‐Period Gravity Waves and Ripples at Davis Station, Antarctica (68°S, 78°E), During the (Austral Winter February–October) Period 1999–2013

AbstractA scanning radiometer deployed at Davis Station, Antarctica (68°S, 78°E), has been recording infrared (1.10–1.65 μm) images of a small region (24 km × 24 km) of the zenith night sky once per minute each austral winter night since February 1999. These images have been processed to extract information on the passage of gravity waves (GWs) (horizontal wavelength, λh > 15 km) and ripples (λh ≤ 15 km) over the observing station. Phase speeds, periods, horizontal wavelengths, and predominant propagation directions have been deduced. Observed speeds were found to be highly correlated with horizontal wavelengths as has been reported in previous studies. Reverse ray tracing of the detected GWs only enabled us to identify four distinct groups. On average, only 15% of waves detected can be traced back to the troposphere, and a large proportion (~45%) were not successfully reverse traced substantially below the airglow layer. Two smaller groups were found to reach a termination condition for reverse ray tracing at altitudes near 50 km and 75 km. Of those that reached the termination altitude in the troposphere (10 km), most of the end points fell within a radius of 300 km of the station, with a very pronounced concentration of wave initiation to the northwest of the observing point. The predominant direction of propagation was southward, and they were observed throughout the year. Recent reports suggest the interaction of planetary waves with the background wind field as a potential source for these waves.

Case Study and Climatological Analysis of Upper-Tropospheric Jet Stream and Stratosphere–Troposphere Exchanges Using VHF Profilers and Radionuclide Measurements in France

AbstractThe authors present a climatological analysis of tropospheric horizontal wind profiles and jet stream events using long series of wind profiles from two VHF profilers located in France: Lannemezan (2001–14) and Opme (1999–2014). A case study of jet stream and stratospheric intrusion of air into the troposphere that occurred in January 2013 is first described and demonstrates the capability of the VHF profilers to detect jet stream events. The climatology study over the two sites reveals the strongest values of seasonal wind during winter (21.4 m s−1at 8.7-km height at Opme; 25.1 m s−1at 9.6-km height at Lannemezan). A methodology based on the automatic detection of maximum winds on a decadal series of hourly wind profiles allows the detection of jet stream events and establishes its climatology for each site. A frequency analysis of jet stream events of westerly winds over 50 m s−1presents a clear seasonality at the two sites, with a maximum in winter (3.5%–9.7% of hourly profiles) and a minimum in summer (near 1%). Cosmogenic radionuclides sampled at Opme also exhibit a clear seasonal variation with maximum in spring and minimum in the cold seasons; the7Be/22Na activity ratio confirms stratosphere-to-troposphere exchanges for the studied cases. The mean interannual variability of the frequency of jet stream events is 1.5% in Opme and 2.9% in Lannemezan. Positive decadal trends are observed for the two sites: +1.6 ± 1.2% decade−1for Opme and +2.4 ± 2.2% decade−1for Lannemezan.

Evaluation and Comparison of TRMM Multi-Satellite Precipitation Products With Reference to Rain Gauge Observations in Hunza River Basin, Karakoram Range, Northern Pakistan

The performance evaluation of satellite-based precipitation products at local and regional scales is crucial for modification in satellite-based precipitation retrieval algorithms, as well as for the provision of guidance during the selection of substitute precipitation data. This study evaluated the performances of three Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) products (3B42V6, 3B42RT and 3B42V7) with a reference to rain gauge observations in the Hunza River basin, northern Pakistan. Multi-spatial (pixel and basin) and temporal (daily, monthly, seasonal and annual) resolutions were considered for performance evaluation of TMPA products. Results revealed that the spatial pattern of observed precipitation over the basin was adequately captured by 3B42V7 but misplaced by 3B42V6 and 3B42RT. All TMPA products were unable to capture the intense precipitation events. On the daily time scale, the performance of TMPA products was very poor over both spatial scales. 3B42V6 underestimated the precipitation (31.25% and 44.27% on pixel and basin scales, respectively). By contrast, 3B42RT significantly overestimated the precipitation (47.91% and 38.62% on pixel and basin scales, respectively), while 3B42V7 showed overestimation (17.30%) on pixel scale and slight underestimation (6.24%) on the basin scale. On the seasonal scale, TMPA products showed significant biases with observed precipitation data. We found that the TMPA products performed relatively better on monthly and annual time scales and overall performance of 3B42V7 product was better than that of 3B42V6 and 3B42RT. The bias in 3B42V7 was improved by 85.90% compared with 3B42V6 and by 116.16% compared with 3B42RT. Thus, it is concluded that the TMPA products were unreliable to capture the intense precipitation events and retain high errors on daily and seasonal scales. Therefore, caution should be considered while using these precipitation estimates as a substitute data in hydrology, meteorology and climatology studies in Hunza River basin. However, due to the reasonable performance of monthly and annual 3B42V7 estimates, these can be used as an acceptable substitute for applications in the region.

Potential Vorticity Diagnostics to Quantify Effects of Latent Heating in Extratropical Cyclones. Part I: Methodology

Abstract Extratropical cyclones develop because of baroclinic instability, but their intensification is often substantially amplified by diabatic processes, most importantly, latent heating (LH) through cloud formation. Although this amplification is well understood for individual cyclones, there is still need for a systematic and quantitative investigation of how LH affects cyclone intensification in different, particularly warmer and moister, climates. For this purpose, the authors introduce a simple diagnostic to quantify the contribution of LH to cyclone intensification within the potential vorticity (PV) framework. The two leading terms in the PV tendency equation, diabatic PV modification and vertical advection, are used to derive a diagnostic equation to explicitly calculate the fraction of a cyclone’s positive lower-tropospheric PV anomaly caused by LH. The strength of this anomaly is strongly coupled to cyclone intensity and the associated impacts in terms of surface weather. To evaluate the performance of the diagnostic, sensitivity simulations of 12 Northern Hemisphere cyclones with artificially modified LH are carried out with a numerical weather prediction model. Based on these simulations, it is demonstrated that the PV diagnostic captures the mean sensitivity of the cyclones’ PV structure to LH as well as parts of the strong case-to-case variability. The simple and versatile PV diagnostic will be the basis for future climatological studies of LH effects on cyclone intensification.

A Long-Term Assessment of the Black Sea Wave Climate

In the present work the Black Sea wave climate is assessed using a total of 38 years of data (1979–2016). As a first step, the long-term variations of the main wave parameters were evaluated using data provided by the European Center for Medium-Range Weather Forecasts (ECMWF). Based on these values, the nearshore and offshore conditions from the Black Sea were evaluated. Moreover, the Sea of Azov was also targeted in this study, since in some cases the conditions are comparable with those of the Black Sea. Going up to the present day, the regional wave climate was assessed through satellite measurements provided by the AVISO project, at the same time indicating the differences between these data and the ECMWF reanalysis dataset. In general, the conditions reported in the northwestern sector of the Black Sea seem to be more energetic, indicating more frequently the presence of rough conditions. Finally, it can be concluded that the results presented in the present study cover a broad range of applications in climatological studies and other types of research related to coastal protection.

New Approaches for Estimation of Monthly Rainfall Based on GEP-ARCH and ANN-ARCH Hybrid Models

Accurate estimation of rainfall has an important role in the optimal water resources management, as well as hydrological and climatological studies. In the present study, two novel types of hybrid models, namely gene expression programming-autoregressive conditional heteroscedasticity (GEP-ARCH) and artificial neural networks-autoregressive conditional heteroscedasticity (ANN-ARCH) are introduced to estimate monthly rainfall time series. To fulfill this purpose, five stations with various climatic conditions were selected in Iran. The lagged monthly rainfall data was utilized to develop the different GEP and ANN scenarios. The performance of proposed hybrid models was compared to the GEP and ANN models using root mean square error (RMSE) and coefficient of determination (R2). The results show that the proposed GEP-ARCH and ANN-ARCH models give a much better performance than the GEP and ANN in all of the studied stations with various climates. Furthermore, the ANN-ARCH model generally presents better performance in comparison with the GEP-ARCH model.

A 1D Theoretical Analysis of Northerly Low-Level Jets over the Great Plains

Abstract The forcing of northerly low-level jets over the eastward-sloped terrain of the U.S. Great Plains was studied using a one-dimensional (1D) nonstationary analytical model based on the Boussinesq-approximated equations of motion and thermal energy. For northerly low-level jets, the forcing from diurnal changes in surface heating of the sloped terrain (Holton mechanism) is out of phase with the nocturnal inertial oscillation resulting from the cessation of turbulent mixing at sunset (Blackadar mechanism), which results in weaker northerly nocturnal low-level jets when compared to southerly nocturnal low-levels jets with the same-magnitude background pressure gradient forcing. Because of the Blackadar and Holton mechanisms acting out of phase, nocturnal northerly low-level jets cannot solely explain the northerly low-level jet maximum over the Great Plains found in climatological studies. It is shown that negative buoyancy values over the eastward-sloped terrain enhance the low-level northerly geostrophic wind, which can cause low-level jetlike wind profiles that do not necessarily depend on the diurnal cycle. However, nocturnal northerly low-level jets primarily caused by an inertial oscillation still occur when daytime mixing is strong and buoyancy is small at sunset. These conditions are possible when strong capping inversions are present in the daytime convective boundary layer. The occurrence of both types of northerly low-level jets, those caused by negative buoyancy values over the sloped terrain and those driven by an inertial oscillation, better explains the findings of previous low-level jet climatologies.

Functional inverted Wishart for Bayesian multivariate spatial modeling with application to regional climatology model data.

Modern environmental and climatological studies produce multiple outcomes at high spatial resolutions. Multivariate spatial modeling is an established means to quantify cross-correlation among outcomes. However, existing models typically suffer from poor computational efficiency and lack the flexibility to simultaneously estimate auto- and cross-covariance structures. In this article, we undertake a novel construction of covariance by utilizing spectral convolution and by imposing an inverted Wishart prior on the cross-correlation structure. The cross-correlation structure with this functional inverted Wishart prior flexibly accommodates not only positive but also weak or negative associations among outcomes while preserving spatial resolution. Furthermore, the proposed model is computationally efficient and produces easily interpretable results, including the individual autocovariances and full cross-correlation matrices, as well as a partial cross-correlation matrix reflecting the outcome correlation after excluding the effects caused by spatial convolution. The model is examined using simulated data sets under different scenarios. It is also applied to the data from the North American Regional Climate Change Assessment Program, examining long-term associations between surface outcomes for air temperature, pressure, humidity, and radiation, on the land area of the North American West Coast. Results and predictive performance are compared with findings from approaches using convolution only or coregionalization.

Deep learning for phenomena-based classification of Earth science images

Automated classification of images across image archives requires reducing the semantic gap between high-level features perceived by humans and low-level features encoded in images. Due to rapidly growing image archives in the Earth science domain, it is critical to automatically classify images for efficient sorting and discovery. In particular, classifying images based on the presence of Earth science phenomena allows users to perform climatology studies and investigate case studies. We present applications of deep learning-based classification of Earth science images.

A time series of annual land use and land cover maps of China from 1982 to 2013 generated using AVHRR GIMMS NDVI3g data

A time series of annual land use and land cover (LULC) maps that cover an extended period of time is a key dataset for climatological studies investigating land-atmosphere interaction. Change in LULC can influence regional climate by altering the surface roughness, soil moisture, heat flux partition, and terrestrial carbon storage. Although annual global LULC maps are generated from Moderate-resolution Imaging Spectroradiometer (MODIS) data, the earliest MODIS LULC map is for 2001, which limits the potential time period for climatological analyses. This study produced a continuous series of annual LULC maps of China from 1982 to 2013 using random forest classification of 19 phenological metrics derived from Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies (GIMMS) third generation NDVI (NDVI3g) data. The classifier was trained using reference data derived from the MODIS land cover type product (MCD12Q1). Based on a comparison with Google Earth images, the overall accuracy of a simplified eight-class version of our 2012 LULC map is 73.8%, which is not significantly different from the accuracy of the MODIS map of the same year. Our maps indicate that for the three decades studied, the area of croplands and forests in China increased, and the area of grasslands decreased. These annual maps of land cover will be an important dataset for future climate studies, and the methodologies used in this study can be applied to other geographical regions where availability of continuous time series of LULC maps is limited.

Global distribution of clay-size minerals on land surface for biogeochemical and climatological studies

Clay-size minerals play important roles in terrestrial biogeochemistry and atmospheric physics, but their data have been only partially compiled at global scale. We present a global dataset of clay-size minerals in the topsoil and subsoil at different spatial resolutions. The data of soil clay and its mineralogical composition were gathered through a literature survey and aggregated by soil orders of the Soil Taxonomy for each of the ten groups: gibbsite, kaolinite, illite/mica, smectite, vermiculite, chlorite, iron oxide, quartz, non-crystalline, and others. Using a global soil map, a global dataset of soil clay-size mineral distribution was developed at resolutions of 2' to 2° grid cells. The data uncertainty associated with data variability and assumption was evaluated using a Monte Carlo method, and validity of the clay-size mineral distribution obtained in this study was examined by comparing with other datasets. The global soil clay data offer spatially explicit studies on terrestrial biogeochemical cycles, dust emission to the atmosphere, and other interdisciplinary earth sciences.

Detection of homogeneous precipitation regions at seasonal and annual time scales, northwest Iran

Abstract Detection of homogeneous climate areas is a challenging issue, which can be affected by different criteria. One of the most prominent factors is choosing the time scale, which can lead to different spatial and temporal patterns. Total precipitation is a key factor in climatological studies, and studying its distribution is of utmost importance. The combination of principal components analysis and cluster analysis is used for homogeneous precipitation areas' detection. Hence, the spatial pattern of total precipitation was investigated in northwestern Iran during the past two decades (1991–2010) on seasonal and annual time scales. The results of clustering on each time scale were validated, and well-defined clusters were investigated and compared with each other. Two homogeneous sub-regions were recognized in spring, the best period for depicting homogeneous precipitation clusters at seasonal resolution. The annual pattern of precipitation delineated three clusters in the study region. Finally, the characteristics of the well-clustered maps reveal the importance of time scale in detection of homogeneous precipitation sub-zones.

Some Features of Surface Air Temperature: A Statistical Viewpoint

A climatological study has been done in five weather stations viz Dhuburi, Guwahati, Silchar, Tezpur and Dibrugarh for 45 years (1969-2013), for studying and comparing maximum, minimum and mean temperatures. Coefficient of variation, skewness, kurtosis are also calculated and plotted for comparing the results of the stations. The values of period mean of annual surface air temperature are different at different stations and this value does not show homogeneous distribution in the regions. The pattern of distribution of annual mean of daily surface air temperature (maximum, minimum and mean) are asymmetrical over all the stations and have different peakedness at different stations means over all the stations that the distribution are deviates from the normal distribution from slight to significant amount. In most of the cases winter months has shown highest variation while summer month are least variable. Variation in spring and autumn months are in between these two extremes. Almost over all the stations, the patterns of distribution of monthly mean temperature (maximum, minimum and mean) are not normal. The distributions are both positively and negatively skewed and have both platykurtic and leptokurtic peakedness.

Are standing dead trees (snags) suitable as climate proxies? A case study from the central Scandinavian Mountains

ABSTRACTStanding dead trees (snags) play important roles in forest ecology by storing carbon as well as providing habitats for many species. Moreover, snags preserved for hundreds of years can provide useful data to extend tree-ring chronologies used for climatological and ecological studies beyond the lifespans of living trees. Here we examined the growth patterns of Scots pine snags from the central Scandinavian Mountains, in relation to still living trees. Using changes point analyses, we showed that a majority (74%) of the snags displayed significant negative growth changes prior (on average 17 years) to death. Change points around the same years were also seen in living trees, but they recovered their growth. The average growth reduction of snags showing negative growth changes before death was 46%. In most cases the final growth change points coincided with very cold summers, or to a lesser degree to period of cool summers. It was suggested that pines ending up as snags were less resilient than the trees which continued living, and thus not able to recover after cold summer events. Since the snag growth reductions prior to death were partly unrelated to climate, care should be taken when using such data in dendroclimatological studies.

Climate and Production: The Case of the Administrative Region of Grande Dourados, Mato Grosso do Sul, Brazil

In the academic literature we can find a wide range of studies in climatology which show that current land management methods are contributing to an increase in environmental impact on the planet. These studies in climatology not only analyze atmospheric data, but also require a wide knowledge of the researcher’s regional interests for territorial planning. This article aims to explain the characteristics and tendencies used in the territory of the administrative region of Grande Dourados, in the state of Mato Grosso do Sul, Brazil, and the environmental implications of this process of land exploration. Then, we analyze several climatological surveys carried out by the physical geography laboratory of the Federal University of Grande Dourados and the socio-economic and environmental research group of Mato Grosso do Sul. The results demonstrate how important it is to develop strong measures to valorize environmental actions in the area. Climatic parameters can also exacerbate more extreme regional climate patterns, an exacerbation that has a strong spatio-temporal aspect, and also has a direct relation to the various climatological scales. This type of research is pioneering work in the state of Mato Grosso do Sul and in Brazil, and it will contribute to further academic work which will discuss the important relations between land production and climate impact in the near future.