Summertime Rainfall Research Articles

Influences of the Monsoon Trough and Arabian Heat Low on Summer Rainfall over the United Arab Emirates

Abstract The factors responsible for rare summertime rainfall over portions of the United Arab Emirates (UAE), which have not been previously explored in detail, are elucidated with the Climate Forecast System Reanalysis and WRF mesoscale model simulations. The simulations show associations between active phases of the southwest Asian monsoon and intensification of the Arabian heat low, leading up to UAE rainfall events. Variability in the location and strength of the Arabian heat low circulation, which differs from the static portrayal in climatological minimum sea level pressure (MSLP), can affect the development of deep convection over the UAE. Analysis of the vorticity equation for a two-day case study period confirms that convergence is solely responsible for the spinup and maintenance of the primary heat low circulation. Convergence is also responsible for the spinup of a separate cyclonic circulation over the eastern UAE, which propagates offshore to the Arabian Gulf during morning hours. This cyclonic circulation advects moist air onshore over the western UAE, and deep convection follows from inland horizontal convective rolls and interaction with the approaching sea-breeze front. The development of widespread deep convection is shown to be most favorable during the decay phase of the Arabian heat low, when the preconditioned moist air is not replaced by drier continental flow, and the vertical profiles of temperature and moisture are also more favorable. Three other rainfall cases are briefly discussed to illustrate how the strength and geographic position of the Arabian heat low can affect rainfall characteristics over the UAE.

Impact of Extensive Urbanization on Summertime Rainfall in the Beijing Region and the Role of Local Precipitation Recycling

AbstractIn this study, we conducted nested high‐resolution simulations using the Weather Research and Forecasting model coupled with a single‐layer urban canopy model to investigate the impact of extensive urbanization on regional precipitation over the Beijing‐Tianjin‐Hebei region in China. The results showed that extensive urbanization decreased precipitation considerably over and downwind of Beijing city. The prevalence of impermeable urban land inhibits local evaporation that feeds moisture into the overlying atmosphere, decreasing relative humidity and atmospheric instability. The dynamic precipitation recycling model was employed to estimate the precipitation that originates from local surface evaporation and large‐scale advection of moisture. Results showed that about 11% of the urbanization‐induced decrease in total precipitation over the Greater Beijing Region and its surroundings was contributed by the decrease in local recycled precipitation, while the other part (89%) was due to decreasing large‐scale advected precipitation. Results suggest that the low evaporation from urban land surfaces not only reduces the supply of water vapor for local recycled precipitation directly but also decreases the convective available potential energy and hence the conversion efficiency of atmospheric moisture into rainfall. The urbanization‐induced variations in local recycled precipitation were found to be correlated with the net atmospheric moisture flux on a monthly time scale.

Errors and uncertainties in regional climate simulations of rainfall variability over Tunisia: a multi-model and multi-member approach

Temporal and spatial variability of rainfall over Tunisia (at 12 km spatial resolution) is analyzed in a multi-year (1992–2011) ten-member ensemble simulation performed using the WRF model, and a sample of regional climate hindcast simulations from Euro-CORDEX. RCM errors and skills are evaluated against a dense network of local rain gauges. Uncertainties arising, on the one hand, from the different model configurations and, on the other hand, from internal variability are furthermore quantified and ranked at different timescales using simple spread metrics. Overall, the WRF simulation shows good skill for simulating spatial patterns of rainfall amounts over Tunisia, marked by strong altitudinal and latitudinal gradients, as well as the rainfall interannual variability, in spite of systematic errors. Mean rainfall biases are wet in both DJF and JJA seasons for the WRF ensemble, while they are dry in winter and wet in summer for most of the used Euro-CORDEX models. The sign of mean annual rainfall biases over Tunisia can also change from one member of the WRF ensemble to another. Skills in regionalizing precipitation over Tunisia are season dependent, with better correlations and weaker biases in winter. Larger inter-member spreads are observed in summer, likely because of (1) an attenuated large-scale control on Mediterranean and Tunisian climate, and (2) a larger contribution of local convective rainfall to the seasonal amounts. Inter-model uncertainties are globally stronger than those attributed to model’s internal variability. However, inter-member spreads can be of the same magnitude in summer, emphasizing the important stochastic nature of the summertime rainfall variability over Tunisia.

The Role of Nonlinear Drying above the Boundary Layer in the Mid-Holocene African Monsoon

Abstract Paleoclimatic proxies indicate that significant summertime rainfall reached the Sahara region during the mid-Holocene, presumably in response to stronger summertime heating in the Northern Hemisphere. Climate models generally do not replicate the enhanced precipitation. As a step toward understanding the response and possible role of model errors, a series of idealized experiments were conducted with the Community Earth System Model in which local atmospheric heat sources of increasing magnitude were applied in the boundary layer over the Sahel and Sahara. In response to this local heating, the cold and moist southwesterly monsoon inflow encroaches farther northward. A source strength of roughly 1 K day−1 produces responses similar to those in a simulation with mid-Holocene orbital forcing imposed globally, while that of 1.5 K day−1 produces a precipitation response similar to that from paleoproxies. The precipitation increases nonlinearly, with a jump at heating of around 1 K day−1, even though the low-level monsoon inflow increases linearly. Competition at low-to-middle levels between drying by a shallow return flow just above the boundary layer and moistening by vertical advection within the layer affects convection and determines the northward extension of precipitation. When the heating becomes 1.5 K day−1, the boundary layer flow encroaches sufficiently northward to weaken the shallow return flow, further aiding precipitation. This novel nonlinear mechanism operates without biogeophysical feedbacks, and suggests that poor representation of the local thermodynamic processes may hamper a model’s ability to simulate dynamical feedbacks and hence the strength and poleward extension of monsoon rains under forcings like those during the mid-Holocene.

A Dipole Pattern of Summertime Rainfall across the Indian Subcontinent and the Tibetan Plateau

The Tibetan Plateau (TP) has long been regarded as a key driver for the formation and variations of the Indian summer monsoon (ISM). Recent studies, however, have indicated that the ISM also exerts a considerable impact on rainfall variations in the TP, suggesting that the ISM and the TP should be considered as an interactive system. From this perspective, the covariability of the July–August mean rainfall across the Indian subcontinent (IS) and the TP is investigated. It is found that the interannual variation of IS and TP rainfall exhibits a dipole pattern in which rainfall in the central and northern IS tends to be out of phase with that in the southeastern TP. This dipole pattern is associated with significant anomalies in rainfall, atmospheric circulation, and water vapor transport over the Asian continent and nearby oceans. Rainfall anomalies and the associated latent heating in the central and northern IS tend to induce changes in regional circulation that suppress rainfall in the southeastern TP and vice versa. Furthermore, the sea surface temperature anomalies in the tropical southeastern Indian Ocean can trigger the dipole rainfall pattern by suppressing convection over the central IS and the northern Bay of Bengal, which further induces anomalous anticyclonic circulation to the south of TP that favors more rainfall in the southeastern TP by transporting more water vapor to the region. The dipole pattern is also linked to the Silk Road wave train via its link to rainfall over the northwestern IS.

Differences and links between the East Asian and South Asian summer monsoon systems: Characteristics and Variability

This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM) systems. The results show obvious differences in summertime rainfall characteristics between these two monsoon systems. The summertime rainfall cloud systems of the EASM show a mixed stratiform and cumulus cloud system, while cumulus cloud dominates the SASM. These differences may be caused by differences in the vertical shear of zonal and meridional circulations and the convergence of water vapor transport fluxes. Moreover, the leading modes of the two systems’ summertime rainfall anomalies also differ in terms of their spatiotemporal features on the interannual and interdecadal timescales. Nevertheless, several close links with respect to the spatiotemporal variabilities of summertime rainfall and water vapor transport exist between the two monsoon systems. The first modes of summertime rainfall in the SASM and EASM regions reveal a significant negative correlation on the interannual and the interdecadal timescales. This close relationship may be linked by a meridional teleconnection in the regressed summertime rainfall anomalies from India to North China through the southeastern part over the Tibetan Plateau, which we refer to as the South Asia/East Asia teleconnection pattern of Asian summer monsoon rainfall. The authors wish to dedicate this paper to Prof. Duzheng YE, and commemorate his 100th anniversary and his great contributions to the development of atmospheric dynamics.

Impacts of Anthropogenic Heat on Summertime Rainfall in Beijing

AbstractAnthropogenic heat is an important component of the urban energy budgets that can affect land surface and atmospheric boundary layer processes. Representation of anthropogenic heat in numerical climate modeling systems is therefore important when simulating urban meteorology and climate and has the potential to improve weather forecasts, climate process studies, and energy demand analysis. Here, spatiotemporally dynamic anthropogenic heat data estimated by the Building Effects Parameterization and Building Energy Model (BEP-BEM) are incorporated into the Weather Research and Forecasting (WRF) Model system to investigate its impact on simulation of summertime rainfall in Beijing, China. Simulations of four local rainfall events with and without anthropogenic heat indicate that anthropogenic heat leads to increased rainfall over the urban area. For all four events, anthropogenic heat emission increases sensible heat flux, enhances mixing and turbulent energy transport, lifts PBL height, increases dry static energy, and destabilizes the atmosphere in urban areas through thermal perturbation and strong upward motion during the prestorm period, resulting in enhanced convergence during the major rainfall period. Intensified rainfall leads to greater atmospheric dry-down during the storm and a higher poststorm LCL.

Characteristics of the Surface Sensible Heat on the Qinghai-Xizang Plateau in the Spring and Its Influences on the Summertime Rainfall Pattern over the Eastern China

Characteristics of the Surface Sensible Heat on the Qinghai-Xizang Plateau in the Spring and Its Influences on the Summertime Rainfall Pattern over the Eastern China

Understanding the Asian summer monsoon response to greenhouse warming: the relative roles of direct radiative forcing and sea surface temperature change

Future hydroclimate projections from state-of-the-art climate models show large uncertainty and model spread, particularly in the tropics and over the monsoon regions. The precipitation and circulation responses to rising greenhouse gases involve a fast component associated with direct radiative forcing and a slow component associated with sea surface temperature (SST) warming; the relative importance of the two may contribute to model discrepancies. In this study, regional hydroclimate responses to greenhouse warming are assessed using output from coupled general circulation models in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) and idealized atmospheric general circulation model experiments from the Atmosphere Model Intercomparison Project. The thermodynamic and dynamic mechanisms causing the rainfall changes are examined using moisture budget analysis. Results show that direct radiative forcing and SST change exert significantly different responses both over land and ocean. For most part of the Asian monsoon region, the summertime rainfall changes are dominated by the direct CO2 radiative effect through enhanced monsoon circulation. The response to SST warming shows a larger model spread compared to direct radiative forcing, possibly due to the cancellation between the thermodynamical and dynamical components. While the thermodynamical response of the Asian monsoon is robust across the models, there is a lack of consensus for the dynamical response among the models and weak multi-model mean responses in the CMIP5 ensemble, which may be related to the multiple physical processes evolving on different time scales.

A simple lightning assimilation technique for improving retrospective WRF simulations

Convective rainfall is often a large source of error in retrospective modeling applications. In particular, positive rainfall biases commonly exist during summer months due to overactive convective parameterizations. In this study, lightning assimilation was applied in the Kain-Fritsch (KF) convective scheme to improve retrospective simulations using the Weather Research and Forecasting (WRF) model. The assimilation method has a straightforward approach: force KF deep convection where lightning is observed and, optionally, suppress deep convection where lightning is absent. WRF simulations were made with and without lightning assimilation over the continental United States for July 2012, July 2013, and January 2013. The simulations were evaluated against NCEP stage-IV precipitation data and MADIS near-surface meteorological observations. In general, the use of lightning assimilation considerably improves the simulation of summertime rainfall. For example, the July 2012 monthly averaged bias of 6 h accumulated rainfall is reduced from 0.54 to 0.07 mm and the spatial correlation is increased from 0.21 to 0.43 when lightning assimilation is used. Statistical measures of near-surface meteorological variables also are improved. Consistent improvements also are seen for the July 2013 case. These results suggest that this lightning assimilation technique has the potential to substantially improve simulation of warm-season rainfall in retrospective WRF applications.

Detection, Attribution, and Projection of Regional Rainfall Changes on (Multi-) Decadal Time Scales: A Focus on Southeastern South America

AbstractObserved austral summertime (November through April) rainfall in southeastern South America (SESA)—including northern Argentina, Uruguay, southern Brazil, and Paraguay—has exhibited substantial low-frequency variations with a multidecadal moistening trend during the twentieth century and a subsequent decadal drying trend during the current century. Understanding the mechanisms responsible for these variations is essential for predicting long-term rainfall changes. Here with a suite of attribution experiments using a pair of high-resolution global climate models, GFDL CM2.5 and FLOR-FA, the authors investigate the causes of these regional rainfall variations. Both models reproduce the twentieth-century moistening trend, albeit with a weaker magnitude than observed, in response to the radiative forcing associated with increasing greenhouse gases. The increasing greenhouse gases drive tropical expansion; consequently, the subtropical dry branch of Hadley cell moves away from SESA, leading to the rainfall increase. The amplitude discrepancy between the observed and simulated rainfall changes suggests a possible underestimation by the models of the atmospheric response to the radiative forcing, as well as an important role for low-frequency internal variability in the observed moistening trend. Over the current century, increasing greenhouse gases drive a continuous SESA rainfall increase in the models. However, the observed decadal rainfall decline is largely (~60%) reproduced in response to the observed Pacific trade wind strengthening, which is likely associated with natural Pacific decadal variability. These results suggest that the recent summertime rainfall decline in SESA is temporary and that the positive trend will resume in response to both increasing greenhouse gases and a return of Pacific trade winds to normal conditions.

Summertime Rainfall Events in Eastern Washington and Oregon

Abstract The temporal and spatial characteristics of summertime rainfall events in the Pacific Northwest are examined in relation to the prevailing regional 500-hPa geopotential height conditions, with focus on the forested slopes of eastern Washington and northeastern Oregon, where the absence/occurrence of events largely determines the start and end of the wildland fire season. The Daily U.S. Unified Precipitation dataset is used for specifying rainfall events (period 1949–2008). Events are defined as one or more consecutive days of rainfall exceeding 0.25 in. (0.65 mm), and occur on average two to three times per summer (July–September) in the focus region, east of the Cascade Mountain crest, with a minimum in frequency in late July. A relatively high percentage of the events in the northern portion of the domain of interest, and over the higher terrain, is associated with anomalous midtropospheric southwesterly flow; a high percentage of the events in the southern and lower elevation portions of the domain is associated with southeasterly flow anomalies. Southeasterly flow events are much more likely to be accompanied by lightning and a more localized rainfall distribution than southwesterly events. Southwesterly events mainly account for the late-July frequency minimum and produce more widespread/heavier precipitation on average. The forests of eastern Washington and Oregon receive a mix of southeasterly and southwesterly events. Results suggest that identifying flow types by (skillful) extended-range 500-hPa forecasts may provide a useful basis for predicting the associated aspects of the rainfall event distribution.

Tropical and Extratropical Controls of Gulf of California Surges and Summertime Precipitation over the Southwestern United States

AbstractIn this study ERA-Interim data are used to study the influence of Gulf of California (GoC) moisture surges on the North American monsoon (NAM) precipitation over Arizona and western New Mexico (AZWNM), as well as the connection with larger-scale tropical and extratropical variability. To identify GoC surges, an improved index based on principal component analyses of the near-surface GoC winds is introduced. It is found that GoC surges explain up to 70% of the summertime rainfall over AZWNM. The number of surges that lead to enhanced rainfall in this region varies from 4 to 18 per year and is positively correlated with annual summertime precipitation. Regression analyses are performed to explore the relationship between GoC surges, AZWNM precipitation, and tropical and extratropical atmospheric variability at the synoptic (2–8 days), quasi-biweekly (10–20 days), and subseasonal (25–90 days) time scales. It is found that tropical and extratropical waves, responsible for intrusions of moist tropical air into midlatitudes, interact on all three time scales, with direct impacts on the development of GoC surges and positive precipitation anomalies over AZWNM. Strong precipitation events in this region are, however, found to be associated with time scales longer than synoptic, with the quasi-biweekly and subseasonal modes playing a dominant role in the occurrence of these more extreme events.

Evaluating the impacts of cumulus, land surface and ocean surface schemes on summertime rainfall simulations over East-to-southeast Asia and the western north Pacific by RegCM4

This study evaluates the sensitivity of summertime rainfall simulations over East-to-southeast Asia and the western north Pacific in the regional climate model version 4 (RegCM4) to cumulus (including Grell with Arakawa–Schubert type closure, Grell with Fritsch–Chappell type closure, and Emanuel), land surface (Biosphere–atmosphere transfer scheme or BATS, and the community land model or CLM) and ocean surface (referred to as Zeng1, Zeng2 and BATS1e in the model) schemes by running the model with different combinations of these parameterization packages. For each of these experiments, ensemble integration of the model was carried out in the extended boreal summer of May–October from 1998 to 2007. The simulated spatial distribution, intensity and inter-annual variation of the precipitation, latent heat flux, position of the subtropical high and tropical cyclone genesis patterns from these numerical experiments were analyzed. Examinations show that the combination of Emanuel, CLM and Zeng2 (E-C-Z2) yields the best overall results, consistent with the fact that physical mechanisms considered in E-C-Z2 tend to be more comprehensive in comparison with the others. Additionally, the rainfall quantity is found very sensitive to sea surface roughness length, and the reduction of the roughness length constant (from 2 × 10−4 to 5 × 10−5 m) in our modified BATS1e mitigates the drastic overestimation of latent heat flux and rainfall, and is therefore preferable to the default value for simulations in the western north Pacific region in RegCM4.

Drivers and effects of Karenia mikimotoi blooms in the western English Channel

Naturally occurring red tides and harmful algal blooms (HABs) are of increasing importance in the coastal environment and can have dramatic effects on coastal benthic and epipelagic communities worldwide. Such blooms are often unpredictable, irregular or of short duration, and thus determining the underlying driving factors is problematic. The dinoflagellate Karenia mikimotoi is an HAB, commonly found in the western English Channel and thought to be responsible for occasional mass finfish and benthic mortalities. We analysed a 19-year coastal time series of phytoplankton biomass to examine the seasonality and interannual variability of K. mikimotoi in the western English Channel and determine both the primary environmental drivers of these blooms as well as the effects on phytoplankton productivity and oxygen conditions. We observed high variability in timing and magnitude of K. mikimotoi blooms, with abundances reaching >1000cellsmL−1 at 10m depth, inducing up to a 12-fold increase in the phytoplankton carbon content of the water column. No long-term trends in the timing or magnitude of K. mikimotoi abundance were evident from the data. Key driving factors were identified as persistent summertime rainfall and the resultant input of low-salinity high-nutrient river water. The largest bloom in 2009 was associated with highest annual primary production and led to considerable oxygen depletion at depth, most likely as a result of enhanced biological breakdown of bloom material; however, this oxygen depletion may not affect zooplankton. Our data suggests that K. mikimotoi blooms are not only a key and consistent feature of western English Channel productivity, but importantly can potentially be predicted from knowledge of rainfall or river discharge.

An improved diagnostic for summertime rainfall along the eastern seaboard of Australia

ABSTRACTThe eastern seaboard of Australia (ESB) is a unique climate entity. A region of complex topography bound by the coastline and the ridge of the Great Dividing Range, the ESB exhibits distinctly different rainfall patterns to the rest of southeastern Australia. As a large percentage of the Australian population resides along the ESB, understanding current and future rainfall variability in this region presents an important and difficult challenge. This challenge is compounded by the inability of most general circulation models to properly resolve the region. This study presents a diagnostic for characterizing the variability in summertime rainfall along the ESB. This simple yet effective East Coast Flow Index (ECFI) infers easterly geostrophic flow from the meridional pressure gradient along the ESB, and vertical circulation from the upper‐level ω field. The ECFI outperforms the common indices for drivers of rainfall variability, achieving statistically significant correlations with ESB summertime rainfall for a range of different timescales. The ECFI is shown to have great potential as a predictor for statistically downscaling rainfall along the ESB as (1) it provides a physical link between large‐scale forcings and local precipitation responses, (2) is capable of capturing multiyear variability and (3) is realistically represented by general circulation models. While the ECFI was designed for the summer months (December–February) it is still capable of performing well in the other seasons, especially spring (September–November).

Big Data, Weathermen and Economists: Never fall in love with a model

The overabundance of data which now characterizes the work environment of meteorologists, data scientists and risk managers requires new methods of data treatment. Thus, Machine Learning entered into weather modelisation. Because they have chosen to work with non-linear models rather than linear ones, weather specialists are presented as quick to adopt new techniques, more suited to the realities they are trying to capture. This even made some say that weathermen had much to teach to economists, who fail to abandon their old econometric ‘recipes’. Does Machine learning really solve all the problems at once? Are Linear Models really outdated?

Climatology and Variability of Precipitation in the Twentieth-Century Reanalysis

Abstract The performance of the Twentieth-Century Reanalysis (20CR) in reproducing observed monthly mean precipitation over the global domain is compared to that of comprehensive reanalyses that also assimilate upper-air and satellite observations [the Climate Forecast System Reanalysis (CFSR), ECMWF Interim Re-Analysis (ERA-Interim), and NCEP–U.S. Department of Energy reanalysis (NCEP2)] and to that of an atmospheric general circulation model (GCM) ensemble simulation [Global Ocean Global Atmosphere (GOGA)] that is forced with observed sea surface temperature (SST). Wintertime rainfall variability in the midlatitude continents and storm tracks is captured with great accuracy, similar to the comprehensive reanalyses, but summertime rainfall is not, probably in consequence of the greater importance of convection in the summer season. Over the tropics, the accuracy of all reanalyses is much less than over the midlatitudes. Over tropical land, the performance of 20CR is better than NCEP2 and similar to ERA-Interim and CFSR, but over the tropical oceans the most recent reanalyses perform significantly better. Across the twentieth century, the clearest gain from the assimilation of a denser observational dataset is the expansion of the area of good skill. A comparison of the accuracy and ensemble spread in the 20CR and GOGA ensembles highlights regions where SST forcing is a stronger source of skill than data assimilation for 20CR. In contrast, for some tropical regions such as the Sahel, the assimilation of sea level pressure is effective in constraining precipitation values—but model biases in the teleconnections with global SST limit the performance of 20CR.

Impacts of a warming marginal sea on torrential rainfall organized under the Asian summer monsoon

Monsoonal airflow from the tropics triggers torrential rainfall over coastal regions of East Asia in summer, bringing flooding situations into areas of growing population and industries. However, impacts of rapid seasonal warming of the shallow East China Sea ECS and its pronounced future warming upon extreme summertime rainfall have not been explored. Here we show through cloudresolving atmospheric model simulations that observational tendency for torrential rainfall events over western Japan to occur most frequently in July cannot be reproduced without the rapid seasonal warming of ECS. The simulations also suggest that the future ECS warming will increase precipitation substantially in such an extreme event as observed in midJuly 2012 and also the likelihood of such an event occurring in June. A need is thus urged for reducing uncertainties in future temperature projections over ECS and other marginal seas for better projections of extreme summertime rainfall in the surrounding areas.

Configuration and validation of a mesoscale atmospheric model for simulating summertime rainfall in Central Alberta

ABSTRACTExtreme precipitation events in Central Alberta have overwhelmed hydraulic structures several times in recent years, and it is generally expected that rainfall intensity in this region will continue to increase over the next several decades. Accurate rainfall projections are thus needed to assess future flood risks and to mitigate the possible impacts of these changes. Such data may be obtained through the use of regional climate models (RCMs), and one in particular, the fifth‐generation NCAR/Penn State mesoscale atmospheric model (MM5), is investigated here. MM5 is used to dynamically downscale European Centre for Medium‐Range Weather Forecast (ECMWF) ERA‐Interim reanalysis data to evaluate its ability to accurately simulate rainfall in Central Alberta over two consecutive summers that represent contrasting precipitation regimes. It is determined that in complex terrain, different RCM preprocessing settings can result in vastly different input data which are used for the model simulation. After optimal preprocessing settings are identified, precipitation data from the resulting simulations are compared with data from Edmonton's local rain gauge network and a High Resolution Precipitation Product (HRPP), Climate Prediction Center (CPC) MORPHing technique (CMORPH). Precipitation data generated by MM5 reveal that this RCM can indeed distinguish between wet (2010) and dry (2009) years, but that simulated rainfall totals tend to be too high during May of both precipitation regimes, particularly during the dry year. This bias is partially attributed to the RCM's inaccurate simulation of available moisture in the presence of local terrain effects, and should be taken into consideration when making projections regarding possible changes to future precipitation conditions in Central Alberta and in other regions with similar climatology.