Lamb Weather Types Research Articles

The influence of synoptic weather regimes on UK air quality: analysis of satellite column NO2

AbstractGroupings of Lamb weather types (LWTs) are used to assess the influence of synoptic meteorology on UK tropospheric column NO2. Composite satellite maps using daily 2005–2011 data show significant NO2 anomalies for each group. Hence, despite large day‐to‐day variability and significant uncertainty in individual retrievals, the satellite data can be used to determine national‐scale column NO2 variations under different meteorological conditions. Under cyclonic conditions, NO2 is reduced, while anticyclonic conditions aid its accumulation, especially during winter, consistent with trapping of surface emissions and slower photochemical processing. This composite dataset can be used to test seasonal simulations of air quality models.

Conditioning model output statistics of regional climate model precipitation on circulation patterns

Abstract. Dynamical downscaling of Global Climate Models (GCMs) through regional climate models (RCMs) potentially improves the usability of the output for hydrological impact studies. However, a further downscaling or interpolation of precipitation from RCMs is often needed to match the precipitation characteristics at the local scale. This study analysed three Model Output Statistics (MOS) techniques to adjust RCM precipitation; (1) a simple direct method (DM), (2) quantile-quantile mapping (QM) and (3) a distribution-based scaling (DBS) approach. The modelled precipitation was daily means from 16 RCMs driven by ERA40 reanalysis data over the 1961–2000 provided by the ENSEMBLES (ENSEMBLE-based Predictions of Climate Changes and their Impacts) project over a small catchment located in the Midlands, UK. All methods were conditioned on the entire time series, separate months and using an objective classification of Lamb's weather types. The performance of the MOS techniques were assessed regarding temporal and spatial characteristics of the precipitation fields, as well as modelled runoff using the HBV rainfall-runoff model. The results indicate that the DBS conditioned on classification patterns performed better than the other methods, however an ensemble approach in terms of both climate models and downscaling methods is recommended to account for uncertainties in the MOS methods.

Winter daily precipitation variability over the East Anglian region of Great Britain and its relationship with river flow

This paper investigates winter (DJF) precipitation variability over East Anglia at the daily and 2 d timescales using rain gauge data from 134 sites. The first three principal components (PCs) explain 80.2% (82.0%) of the variance in daily (2 d totals). Precipitation displays higher spatial coherence in winter, with the first three PCs of summer daily totals (Neal and Phillips, 2009, International Journal of Climatology 29: 1661–1679) explaining only 72.3% of the variance. The winter PCs for both 24- and 48-h timescales display precipitation maxima in South Essex (PC 1), NE Norfolk (PC 2), and NW Cambridgeshire (PC 3). The rainfall maximum over South Essex is more important in winter than in summer. Lamb Weather Types and synoptic charts are used to explain the causes of the PCs. A precipitation regionalization is also produced. Discharge for 11 rivers is then modelled as a linear function of the rainfall patterns (as represented by the PC scores). With the exception of the River Babingley, whose discharge is not significantly related to the PCs, these models explain on average 26.5% of the variance. For most rivers, there are significant relationships between discharge and precipitation that fell up to 4 d ago on average. In general, East Anglian river flows show persistence over 6–8 d.

Lamb weather types derived from reanalysis products

AbstractWeather typing, based on surface pressure charts, has been one of the principal means of analysis in synoptic climatology. Here, we summarize the history of manual and automated schemes, in the northwest European context, illustrating how the approaches can take advantage of the extended reanalysis products that have recently become available. The British Isles and the associated Lamb weather types (LWTs) are the focus of this study, but the approach can be applied to any mid‐to‐high latitude region to provide series back to 1871. However, caution is advised in the use of the approach where the quality and quantity of input data into the extended reanalysis are known to be temporally and spatially variable and/or poor in early years. This study intercompares the use of automated schemes with operational analyses, reanalyses and earlier manually derived LWTs. Copyright © 2012 Royal Meteorological Society

Connection between NAO, weather types and precipitation in León, Spain (1948–2008)

AbstractThe variability of winter precipitation in the west of the Iberian Peninsula is strongly affected by the North Atlantic Oscillation (NAO). This study focuses on identifying the relationship that exists between precipitation registered in the city of León (in northwestern Spain), the NAO index and the associated weather type during the same period. In order to achieve this objective, the prevailing weather type has been calculated for each day in León from January 1948 to March 2009, using the objective Lamb Weather Types classification method. The most significant results appear in winter (from December to March). During these months an increase has been observed in the frequency of ‘anticyclonic’ weather type (A) (very dry), and a decrease in the ‘cyclonic’ (C), ‘south‐westerly’ (SW) and ‘westerly’ (W) types (the three rainiest weather types). The positive trend in the NAO index could be the main cause of the decrease in the frequency of the three rainiest weather types (C, SW and W) and therefore, responsible for the relevant decline in winter precipitation observed in the city of León. The high correlation coefficients between the NAO index, the frequency of the three rainiest weather types and winter precipitation suggests an interesting method to forecast rainfall. Using a binary logistic regression model, a downscaling model for daily precipitation has been obtained based on the weather types and the NAO index. The daily results obtained for the winter months are good (TSS = 0.64) bearing in mind that only sea level pressure data were used in the logistic model. Copyright © 2011 Royal Meteorological Society

The relationship between Lamb weather types and long‐term changes in flood frequency, River Eden, UK

AbstractResearch has found that both flood magnitude and frequency in the UK may have increased over the last five decades. However, evaluating whether or not this is a systematic trend is difficult because of the lack of longer records. Here we compile and consider an extreme flood record that extends back to 1770. Since 1770, there have been 137 recorded extreme floods. However, over this period, there is not a unidirectional trend of rising extreme flood risk over time. Instead, there are clear flood‐rich and flood‐poor periods. Three main flood‐rich periods were identified: 1873–1904, 1923–1933, and 1994 onwards. To provide a first analysis of what is driving these periods, and given the paucity of more sophisticated datasets that extend back to the 18th century, objective Lamb weather types were used. Of the 27 objective Lamb weather types, only 11 could be associated with the extreme floods during the gauged period, and only 5 of these accounted for > 80% of recorded extreme floods The importance of these five weather types over a longer timescale for flood risk in Carlisle was assessed, through calculating the proportion of each hydrological year classified as being associated with these flood‐generating weather types. Two periods clearly had more than the average proportions of the year classified as one of the flood causing weather types; 1900–1940 and 1983–2007; and these two periods both contained flood‐rich hydrological records. Thus, the analysis suggests that systematic organisation of the North Atlantic climate system may be manifest as periods of elevated and reduced flood risk, an observation that has major implications for analyses that assume that climatic drivers of flood risk can be either statistically stationary or are following a simple trend. Copyright © 2011 Royal Meteorological Society

Have Meteorological Conditions Reduced NO2 Concentrations from Local Emission Sources in Gothenburg?

The risks of exceeding EU limit values for NO2 concentrations have increased in many European cities, and compliance depends strongly on meteorological conditions. This study focuses on meteorological conditions and their influences on urban background NO2 concentrations in the city of Gothenburg for 1999–2008. The relations between observed NO2 concentrations and meteorological conditions are constructed using two modelling approaches: multiple linear regression and synoptic regression. Both approaches assume no trends in emissions over the study period. The multiple linear regression model is established on observed local meteorological variables. The synoptic-regression model first groups days according to synoptic conditions using Lamb Weather Types and then uses linear regression on each group separately. A model comparison shows that linear regression model and synoptic-regression model perform satisfactory. The synoptic-regression model gives higher explained variance (R 2) against observations during the calibration years (1999–2007), in particular for the morning peak and afternoon–evening peak concentrations, but the improvement in the validation period is weak. The annual mean NO2 variations, and their trends during the study period, were assessed using the synoptic-regression model. The synoptic-regression model is able to explain 54%, 42% and 80% of the annual variability of daily mean, morning peak and afternoon–evening peak NO2 concentrations, respectively. The observed and modelled annual means of the daily mean and morning/afternoon–evening peak NO2 concentrations show decreasing trends from 1999 to 2008. All trends, except the trend in annual-average observed morning peak NO2 are statistically significant. The presence of trends in the modelled NO2 concentrations—even though emissions are assumed to be constant—leads us to conclude that weather and climate alone are responsible for a substantial fraction of the recent declines in observed NO2 concentrations in Gothenburg. Favourable meteorological conditions may have mitigated increases in local NO2 emissions during 1999 to 2008.

The impact of weather and atmospheric circulation on O<sub>3</sub> and PM<sub>10</sub> levels at a rural mid-latitude site

Abstract. In spite of the strict EU regulations, concentrations of surface ozone and PM10 often exceed the pollution standards for the Netherlands and Europe. Their concentrations are controlled by (precursor) emissions, social and economic developments and a complex combination of meteorological actors. This study tackles the latter, and provides insight in the meteorological processes that play a role in O3 and PM10 levels in rural mid-latitudes sites in the Netherlands. The relations between meteorological actors and air quality are studied on a local scale based on observations from four rural sites and are determined by a comprehensive correlation analysis and a multiple regression (MLR) analysis in 2 modes, with and without air quality variables as predictors. Furthermore, the objective Lamb Weather Type approach is used to assess the influence of the large-scale circulation on air quality. Keeping in mind its future use in downscaling future climate scenarios for air quality purposes, special emphasis is given to an appropriate selection of the regressor variables readily available from operational meteorological forecasts or AOGCMs (Atmosphere-Ocean coupled General Circulation Models). The regression models perform satisfactory, especially for O3, with an (R2 of 57.0% and 25.0% for PM10. Including previous day air quality information increases significantly the models performance by 15% (O3) and 18% (PM10). The Lamb weather types show a seasonal distinct pattern for high (low) episodes of average O3 and PM10 concentrations, and these are clear related with the meteorology-air quality correlation analysis. Although using a circulation type approach can provide important additional physical relations forward, our analysis reveals the circulation method is limited in terms of short-term air quality forecast for both O3 and PM10 (R2 between 0.12 and 23%). In summary, it is concluded that the use of a regression model is more promising for short-term downscaling from climate scenarios than the use of a weather type classification approach.

Relationship between atmospheric circulation types over Greece and western–central Europe during the period 1958–97

AbstractAn attempt is made to examine the relationship of the surface circulation prevailing over Europe with the corresponding surface and 500 hPa over Greece by correlating Lamb weather types for western Europe and Hess and Brezowsky (HB) types for central Europe with those derived from a new classification scheme for the Greek area. It was found that it was difficult to formulate rules controlling the frequency distributions of the circulation types over the Greek area in relation to the circulation over western and central Europe. However, statistically significant correlation was found between certain types with high frequency, which is greater between Lamb and HB types with the surface circulation types over the Greek area, compared with 500 hPa circulation types. For the most correlated pairs, seasonal composites of mean sea‐level pressure and 500 hPa geopotential height anomalies demonstrated that the formation of the circulation types over the Greek area depends on the extent, intensity of the anticyclonic or cyclonic centres, air mass characteristics, and stability profile in the lower troposphere over the regions examined, but especially over the central and eastern Mediterranean. Copyright © 2004 Royal Meteorological Society

Precipitation and the North Atlantic Oscillation: a study of climatic variability in northern England

AbstractVariations in precipitation in Yorkshire, UK, are linked to large‐scale atmospheric circulation using the North Atlantic Oscillation (NAO) index, objective Lamb weather types, and long‐term seasonal and annual precipitation indices at seven sites. Since the 1960s, a significant decrease in summer precipitation has been observed across the region, with increasing winter precipitation at western locations since 1970. At western sites, precipitation is highly correlated to the NAO, with positive and negative winter‐NAO indices producing anomalies from the long‐term winter precipitation average of 112% and 77% respectively. The recent winter half‐year precipitation increase is concentrated in March and related to a large increase in monthly NAO and the increased occurrence of westerly weather types. The decrease in summer precipitation, however, is caused by both declining receipt from westerly weather types and their decreased occurrence. This is significantly correlated to a decreasing summer index for the NAO. The NAO, the frequency of weather types and precipitation totals are all intimately linked on an annual and monthly time scale. Strong connections between winter precipitation and the NAO may prove very important, particularly in western Yorkshire where most surface water supplies are located. If the NAO can be predicted using sea‐surface temperature, it may allow the estimation of winter reservoir replenishment in western Yorkshire a few months in advance. This may provide an important predictor of future hydrological drought episodes and facilitate forward planning and management of water resource systems located in climatologically similar regions of the UK. Copyright © 2002 Royal Meteorological Society

A stochastic rainfall model for the assessment of regional water resource systems under changed climatic condition

Abstract. A stochastic model is developed for the synthesis of daily precipitation using conditioning by weather types. Daily precipitation statistics at multiple sites within the region of Yorkshire, UK, are linked to objective Lamb weather types (LWTs) and used to split the region into three distinct precipitation sub-regions. Using a variance minimisation criterion, the 27 LWTs are clustered into three physically realistic groups or ‘states'. A semi-Markov chain model is used to synthesise long sequences of weather states, maintaining the observed persistence and transition probabilities. The Neyman-Scott Rectangular Pulses (NSRP) model is then fitted for each weather state, using a defined summer and winter period. The combined model reproduces key aspects of the historic precipitation regime at temporal resolutions down to the hourly level. Long synthetic precipitation series are useful in the sensitivity analysis of water resource systems under current and changed climatic conditions. This methodology enables investigation of the impact of variations in weather type persistence or frequency. In addition, rainfall model statistics can be altered to simulate instances of increased intensity or proportion of dry days for example, for individual weather groups. The input of such data into a water resource model, simulating potential atmospheric circulation changes, will provide a valuable tool for future planning of water resource systems. The ability of the model to operate at an hourly level also allows its use in a wider range of hydrological impact studies, e.g. variations in river flows, flood risk estimation etc. Keywords: water resources; climate change; impacts; stochastic rainfall model; Lamb weather types

The influence of climate on air and precipitation chemistry over Europe, and downscaling applications to future acidic deposition

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 14:7-24 (2000) - doi:10.3354/cr014007 The influence of climate on air and precipitation chemistry over Europe and downscaling applications to future acidic deposition Julie M. Jones1,*, Trevor D. Davies2 1Institute of Hydrophysics, GKSS, Max-Planck-Strasse, 21502 Geesthacht, Germany 2School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom *E-mail: jones@gkss.de ABSTRACT: Atmospheric circulations, and related climate conditions, exert a strong influence on the transport and ultimate deposition of atmospheric pollutants. One potential outcome of climate change is alteration of atmospheric circulation patterns. The first stage in the development of a downscaling methodology to assess the influence of these possible future atmospheric circulation changes on transport and deposition of atmospheric pollutants over Europe is described. Firstly, the main modes of regional-scale circulation over a domain covering the North Atlantic and Europe are determined using principal components analysis of sea level pressure patterns. To determine whether the principal components represent circulation types found in reality, and show realistic relationships with surface temperature and precipitation amount, they are compared to the Lamb Weather Types, Central England Temperature, and England and Wales Rainfall. There are statistically significant relationships between some of the principal components and aqueous and ambient pollutant concentrations at 5 selected stations from the European Monitoring and Evaluation Programme monitoring network. Although, for any one combination of principal component and pollutant variable, the level of explanation can be quite small, notwithstanding some levels of variance explained for individual combinations being up to 69% (45% for the winter season, described in detail here). Because the pollution climate at any one location is a function of many combinations of circulation/pollution relationships, despite the relatively small magnitude of variance explained for individual combinations in this study, the results confirm the utility of atmospheric circulation principal components in deriving downscaling relationships for surface pollution behaviour (via eventual multiple regressions, not reported in this paper), as well as giving further insight into the climatic influences on air and precipitation chemistry over Europe. KEY WORDS: Acidic deposition · Air pollution · Downscaling · Synoptic climatology · Principal components analysis · Climate change Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 14, No. 1. Online publication date: January 24, 2000 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2000 Inter-Research.

Changing headwater suspended sediment yields in the LOIS catchments over the last century: a paleolimnological approach

This paper describes the methods used to reconstruct suspended sediment yields over the last century, based on 210Pb and 137Cs dated bottom sediments in nine lake and/or reservoir catchments. Magnetic susceptibility and dry bulk density are used to correlate between multiple cores taken from each lake/reservoir basin in order to estimate sediment influx through time and reconstruct sediment yield histories. The catchments represent a range of morphological and land use systems, including upland moorland, upland forestry and upland and lowland agricultural systems. The reconstruction provides some background information on pre-20th century sediment yields and permits an evaluation of the effect of 20th century land management systems, especially upland afforestation and agriculture, on changing suspended sediment yields. Reconstructed sediment yields over the last century range from c. 7 to 86 t km−2 yr−1. Average post-1953 yields from pasture, arable, moorland and forested catchments are 13, 31, 29 and 13 t km−2 yr−1, respectively. The history of human disturbance in individual catchments is clearly recorded in the reconstructed sediment yields. Short-lived disturbance, such as afforestation, produces high yields (over 40 t km−2 yr−1) for up to a decade after planting, but yields subsequently decline to pre-planting levels (c. 12 t km−2 yr−1). Sustained increases in sediment yield are associated with arable, mixed agricultural and, to a lesser extent, grazing systems. While the strong controls exerted on sediment yield by human disturbance mask the potential effect of regional contrasts in runoff and topography between catchments, there is some evidence to suggest that a long-term climate change signal is recorded in the temporal trends in sediment yield from an analysis of Lamb weather types. Copyright © 1999 John Wiley & Sons, Ltd.

The use of weather types and air flow indices for GCM downscaling

A variety of different methods have been proposed for downscaling large-scale General Circulation Model (GCM) output to the time and space scales required for climate impact studies. Using weather types to achieve this goal provides greater understanding of the problems that are involved compared to the many “black box” techniques that have been proposed. Analyses using Lamb weather types, counts of weather fronts and air flow indices over the British Isles show strong relationships with daily rainfall characteristics such as the probability and amount of rainfall. Three versions of a weather type method are described for generating daily rainfall series. Two methods use an objective scheme to classify daily circulation types over the British Isles along the lines of Lamb's subjective classification. The third method is based on user-defined categories of vorticity. Each method categorises rainfall events according to whether the previous day was wet or dry. All three methods successfully reproduce the monthly means, persistence and interannual variability of two daily rainfall time series during a validation period. A significant advantage of using vorticity is that it is a continuous variable and is strongly related to the probability of rainfall and the magnitude of rainfall events. The paper ends with a discussion of the issues relevant to the application of this method to the development of climate scenarios from GCMs.

Modelling low-frequency rainfall events using airflow indices, weather patterns and frontal frequencies

Low-frequency, high-magnitude daily rainfall amounts recorded at several sites in central and southern England were related to the prevailing Lamb Weather Types (LWTs), daily weather front and airflow data. Three statistically distinct weather-type clusters were indentified and used to construct a simplified frontal model of daily precipitation occurrence/amount. The model was calibrated against station data for the period 1970–1990 and used to reconstruct observed daily precipitation between 1875 and 1969 given the historic sequence of LWTs. Although the model reproduced the incidence of low-frequency, high-magnitude events, it failed to capture variations in mean wet day probabilities and wet/dry spell persistence. This inability was attributed to the general limitations of the weather classification methodology, which did not capture all aspects of the precipitation regime with equal levels of proficiency. Therefore, the prospects for downscaling high-resolution precipitation series directly from indices of mean sea-level pressure rather than via weather patterns was discussed. Preliminary results indicate that relationships can be established between mean daily precipitation occurrence and airflow indices such as vorticity and strength of air flow. However, further research is required to establish the value of such indices for modelling low-frequency, high-magnitude precipitation events.

The utility of a drought index for assessing the drought hazard in Devon and Cornwall, South West England

The utility of a drought severity index, based on accumulated monthly precipitation deficits and a three-monthly initiation and termination rule, for assessing the variability in the timing and severity of the drought hazard between four selected locations in Devon and Cornwall since 1957 is documented. The robustness of the drought events identified is then assessed by changing the index formulation rules. Results indicate that, using a six-monthly, rather than a three-monthly, rule, drought sequences are more difficult to initiate and terminate and are more persistent with a longer mean duration. The drought severity indices are then used to define a hierarchy of significant drought events, isolated in terms of the number of indices simultaneously exceeding an arbitrarily defined severity. Seven Class I droughts, regional in extent, are then discussed; and circulation contrasts between events highlighted using aggregated Lamb weather types. Two drought sub-types emerge, distinguishable according to whether the controlling anticyclone had a greater tendency to be located to the north and east of the UK or to the south and west. A comparative analysis of the ongoing 1995–drought, in terms of its persistence, and rapidity of onset and cessation, is also conducted. Copyright © 1998 Royal Meteorological Society

Rainfall variability associated with Lamb weather types: The case for incorporating weather fronts

AbstractThe value of weather generators for down‐scaling the output of general circulation models for regional impact assessments is limited by the assumption of stationary‐rainfall‐circulation‐pattern relationships. This note assesses the potential of incorporating weather front data into existing stochastic precipitation models to describe intraweather pattern rainfall variability.

Precipitation over Scotland, 1757–1992: Some aspects of temporal variability

AbstractA 236‐year time series (1757–1992) of monthly areal average precipitation for Scotland is produced using the ‘official’ record compiled by the Meteorological Office (UKMO) from 1869 onwards, corrected for known inhomogeneities, and extended back to 1757 using previously unpublished data from the UKMO. The complete series is evaluated and examined for fluctuations and extreme values with particular reference to observed precipitation increases over the last two decades. Recent increases in annual precipitation, and associated seasonal variations, are judged to be unusual despite the recognition of a longer term trend to higher annual and winter values. Correlations of precipitation since 1869 with Lamb weather types show differences within the record and from other work, which suggest that this index does not fully capture the synoptic conditions relevant to precipitation over Scotland as a whole. The series since 1869 was also used to test the predictive value of climatic normals for 3, 5, 10, 15, 20, and 25 years alongside the standard 30‐year averages of precipitation. It is suggested that the best estimate of seasonal and annual precipitation totals for the following year can be achieved by the application of 3‐ and 5‐year normals, rather than by using precipitation averages of longer duration.

A Review of Ozone Pollution in the United Kingdom and Ireland with an Analysis Using Lamb Weather Types

The control exercised by synoptic airflows on hourly ground level concentrations of ozone at 11 widely distributed monitoring sites in the UK during the period 1986/7-1990 is investigated. Regional airflows are categorized using the seven primary Weather Types of the Lamb (1972) Catalogue. Because of the complexity of troposheric ozone production, transport and decay, relationships vary between sites and the Lamb Weather Types (LWTs). Results confirm the dominant role of stable anticyclonic and easterly airflows at all sites in producing peak ozone episodes via photochemical action. More unstable systems such as the vigorous Westerlies and cyclonic depressions are important in elevating mean ozone concentrations at remote sites through turbulent down-mixing. The study also contrasts the different ozone destruction mechanisms at urban and rural sites. The distribution of hourly ozone values associated with anticyclonic and cyclonic airflows at selected sites shows distinctive ozone signatures. Prospects for modelling the relationship between hourly ground-level ozone concentrations and daily weather are suggested.

Stochastic weather type simulation for regional climate change impact assessment

A stochastic model is developed for the synthesis of daily precipitation by weather type analysis. Daily rainfall at two sites in southern England is related to the Lamb weather types by using conditional probabilities. Time series of circulation patterns and hence rainfall are then generated using a Markov representation of matrices of transition probabilities between weather types. The model reproduces key aspects of the historic rainfall regime at daily, monthly, and annual temporal resolutions. The general validity of the methodology as a means of disaggregating general circulation model predictions into finer spatial scales for water resource studies is discussed. Several limitations are identified of which the subjectivity introduced by the weather type classification system and the nonstationarity of the precipitation characteristics are the most serious.