Lamb Weather Types Research Articles

Extension and trend of the London urban heat island under Lamb weather types

Understanding and describing how urban heat islands evolve is important, given the noticeable impact they have on people living in cities. This paper considers the London heat island from gridded values with one-arcminute spatial resolution over a 33-year period, from 1990 to 2022. Among the available variables in the database, maximum and minimum air temperatures were used. A cold island was not observed, since temperatures in the city centre were higher than those in the surroundings during the day and at night. However, the urban heat island extension was higher for the maximum temperature, whereas this island was limited to the city centre for the minimum temperature, in line with the area delimited by the congestion charge. Lamb weather types were determined, and it was found that the anticyclonic type prevailed, followed by southwest, west, and cyclonic types. The difference between both temperatures was about 6.8 °C in the city centre, and was particularly defined for anticyclonic and cyclonic types. Moreover, anticyclonic situations were linked with the highest urban heat island intensities for minimum temperature. Finally, the temperature trend was similar for both temperatures –about 0.2–0.3 °C/10 years in the city centre– thereby offering a possible quantification of climate change.

The London pollution island under Lamb weather types

This study considers the daily values of gridded concentrations for NO2, O3, PM10 and PM2.5 in London and its surroundings over 2007–2011. A two-step procedure was used for concentration smoothing to observe the urban pollution island. In the first step, the elliptic fit was compared with fits from the Gaussian and Epanechnikov kernels. The results obtained for the Gaussian kernel were used to apply an elliptic fit and a Gaussian directional fit. Lamb weather types were also determined. As a result, the elliptic fit calculated extended concentrations against those calculated with the kernels, and the Gaussian kernel provided a smoother shape. NO2 and O3 presented the opposite distribution, and the urban pollution island was defined with contrasted concentration values between the city centre and the surrounding areas. The second smoothing simplified the urban shape and determined the background concentrations. The most frequent type was the anticyclonic, although the most contrasting result was obtained for the anticyclonic type with SE flow, since O3 values were low compared to the high NO2 values, thereby revealing pollution transport from the continent under this infrequent type. Finally, the urban pollution island shape is maintained for NO2 and O3 under the most frequent weather types.

Climate change in the Iberian Peninsula by weather types and temperature

The main advantage of classifying weather types is its systematic use with pressure gridded values. In this paper, an extensive database covering 74 years was used to determine weather types and their temperature fields in the Iberian Peninsula. Moreover, two 37-year periods were compared to investigate climate change in this region. Lamb weather types were determined. The most frequent was the anticyclonic type (21%) followed by the unclassified type (16.5%), with the distribution of these weather types being nearly similar over time. The pressure field was quite uniform in the region and pressure increased 0.7 hPa between the two periods. Moreover, pressure of easterly flows was greater than the pressure of westerly flows, with their difference being around 7 hPa, and the centres of cyclonic types were closer to the Iberian Peninsula than the centres of the anticyclonic types. Isotherms follow geographic parallels, although the meridian gradient was greater over the continental surface than over the ocean. Northern Africa proved to be prominent, since temperatures were highest and specific flows might favour heat waves over the peninsula. The temperature increase between the two 37-year periods was 0.5 °C. In addition, the contrast between the meridian gradients in the east and west of the region evolved towards a lower contrast of these meridian gradients throughout the whole of the region.

Relation Between Atmospheric Circulation Patterns in the North Atlantic and the Sea States in the Iberian Peninsula

Abstract A statistical analysis of significant wave height (Hs) in a location offshore Portugal continental coast, Leixões, is performed. The spectral and parametric information of sea states at this point used in this analysis was obtained from a 21-year hindcast simulation using the spectral wave model simulating wave nearshore (SWAN) forced by wind fields produced by the Weather Research and Forecasting (WRF) model forced by the ERA-Interim reanalysis. The modeling of the climatic variability of directional spectra provides information of the shape of the expected directional spectra in the various sea states at these locations, i.e., how the spectral parameters and their probability of occurrence change in the regions studied. The occurrences of spectral classes are estimated, and for each class, the variability of the spectral parameters is described by means of joint distributions. The classification of the different sea states provides important information about the wave conditions present in the target areas. A relation between the sea states and the Lamb weather types (WTs) as well as a methodology for classifying atmospheric circulation patterns is presented in this study. The results of this study provide a description of the wave climate through demonstration of the interaction between sea states and weather patterns and relating different circulation patterns to different sea states. This study provides useful information on the wave conditions that can be utilized in the design of ocean engineering structures as well as in the assessment of the operability and safety of shipping and renewable energy devices.

Evaluation of the EURO‐CORDEX Regional Climate Models Over the Iberian Peninsula: Observational Uncertainty Analysis

AbstractThis work evaluates the daily precipitation and mean temperature of eight CORDEX‐EUR11 ERA‐Interim‐driven simulations of EURO‐CORDEX over the Iberian Peninsula (IP) for the period 1989–2008. To this aim, three observational data sets (Iberia01, E‐OBS‐v19e, and MESAN‐0.11) were considered as reference and compared with the models by means of several indices reflecting the mean and extreme regimes over the IP. For precipitation the Lamb weather types were considered to identify synoptic conditions related with higher observational uncertainty. RCMs are able to reproduce the spatial pattern and the variability observed in the IP. However, there is a higher agreement between models and observations for mean temperature than for precipitation, decreasing when extremes are analyzed. For the observational uncertainty analysis, also extreme daily temperatures were considered to obtain a wider picture of this topic. A higher dependence on the observational data set has been found for precipitation than for temperature. This uncertainty is particularly significant when the 50‐year return value is considered for which the observational uncertainty doubles the model uncertainty. Only the wet‐day frequency presents values lower than 0.5 for all seasons, with most of the rest of values reflecting a similar contribution of both components to the uncertainty. In the case of temperatures, the main contribution of the observations has been found when the lower (MAE01) and upper (MAE99) extremes are considered, with values lower than 0.5. For precipitation the observational uncertainty increases when synoptic patterns affecting the Mediterranean Basin are considered, reflecting the difficulty to properly capture the Mediterranean precipitation regimes.

Quantifying the transboundary contribution of nitrogen oxides to UK air quality

AbstractNitrogen dioxide (NO2) pollution is an important contributor to poor air quality (AQ) and a significant cause of premature deaths in the UK. Although transboundary (i.e., international) transport of pollution to the UK is believed to have an impact on UK pollutant concentrations, large uncertainties remain in these estimates. Therefore, the extent to which emission reductions in neighbouring countries would benefit UK AQ relative to local emission reductions also remains unknown. We have used a back‐trajectory model in conjunction with synoptic scale classifications of UK circulation patterns (Lamb Weather Types [LWT]), to quantify the accumulation of nitrogen oxide (NO x = NO2 + NO) emissions in air masses en‐route to the UK. This novel method presents a computationally inexpensive and useful method of quantifying the accumulation of pollutants under different circulation patterns. We find the highest accumulated NO x totals occur under south‐easterly and southerly flows (>15 μg⋅m−2), with a substantial contribution from outwith the UK (>25%). In contrast, the total accumulated NO x under northerly and westerly flows is lower (∼10 μg⋅m−2), and dominated by UK emissions (>95%). This indicates that European emissions can contribute substantially to UK local‐scale pollution in urban areas under south‐easterly and southerly flows. The sensitivity of integrated NO x emission totals under different air masses is investigated by modelling future European emission contributions based on emission reduction targets. Under targets set by the European Union, there would be a decrease in accumulated NO x emissions in London under most wind directions except for north‐westerly, westerly and northerly flow. The largest benefits to UK AQ from transboundary contributions occur with emission reductions in the Benelux region, due to its close proximity and high NO x emission rates, emphasising the importance of international cooperation in improving local AQ.

Past and Projected Weather Pattern Persistence with Associated Multi-Hazards in the British Isles

Hazards such as heatwaves, droughts and floods are often associated with persistent weather patterns. Atmosphere-Ocean General Circulation Models (AOGCMs) are important tools for evaluating projected changes in extreme weather. Here, we demonstrate that 2-day weather pattern persistence, derived from the Lamb Weather Types (LWTs) objective scheme, is a useful concept for both investigating climate risks from multi-hazard events as well as for assessing AOGCM realism. This study evaluates the ability of a Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model sub-ensemble of 10 AOGCMs at reproducing seasonal LWTs persistence and frequencies over the British Isles (BI). Changes in persistence are investigated under two Representative Concentration Pathways (RCP8.5 and RCP4.5) up to 2100. The ensemble broadly replicates historical LWTs persistence observed in reanalyses (1971–2000). Future persistence and frequency of summer anticyclonic LWT are found to increase, implying heightened risk of drought and heatwaves. On the other hand, the cyclonic LWT decreases in autumn suggesting reduced likelihood of flooding and severe gales. During winter, AOGCMs point to increased risk of concurrent fluvial flooding-wind hazards by 2100, however, they also tend to over-estimate such risks when compared to reanalyses. In summer, the strength of the nocturnal Urban Heat Island (UHI) of London could intensify, enhancing the likelihood of combined heatwave-poor air quality events. Further research is needed to explore other multi-hazards in relation to changing weather pattern persistence and how best to communicate such threats to vulnerable communities.

Process‐based evaluation of the VALUE perfect predictor experiment of statistical downscaling methods

Statistical downscaling methods (SDMs) are techniques used to downscale and/or bias‐correct climate model results to regional or local scales. The European network VALUE developed a framework to evaluate and inter‐compare SDMs. One of VALUE's experiments is the perfect predictor experiment that uses reanalysis predictors to isolate downscaling skill. Most evaluation papers for SDMs employ simple statistical diagnostics and do not follow a process‐based rationale. Thus, in this paper, a process‐based evaluation has been conducted for the more than 40 participating model output statistics (MOS, mostly bias correction) and perfect prognosis (PP) methods, for temperature and precipitation at 86 weather stations across Europe.The SDMs are analysed following the so‐called “regime‐oriented” technique, focussing on relevant features of the atmospheric circulation at large to local scales. These features comprise the North Atlantic Oscillation, blocking and selected Lamb weather types and at local scales the bora wind and the western Iberian coastal‐low level jet.The representation of the local weather response to the selected features depends strongly on the method class. As expected, MOS is unable to generate process sensitivity when it is not simulated by the predictors (ERA‐Interim). Moreover, MOS often suffers from an inflation effect when a predictor is used for more than one station. The PP performance is very diverse and depends strongly on the implementation. Although conditioned on predictors that typically describe the large‐scale circulation, PP often fails in capturing the process sensitivity correctly. Stochastic generalized linear models supported by well‐chosen predictors show improved skill to represent the sensitivities.

Deriving Lamb weather types suited to regional climate studies: A case study on the synoptic origins of precipitation over Ireland

The Lamb weather type (LWT) categorization system is one of the best known procedures for summarizing the synoptic circulations that regulate daily weather. Traditionally, it is applied to daily sea level pressure, centred on a domain over the British Isles (BI), which is classed into one of 27 types (or 7 main types). The available register of LWTBI extends to the mid‐19th century and has provided a valuable context for understanding the reasons for temporal and spatial variations in recorded weather elements, especially precipitation. Much of what is known of the synoptic origins of precipitation in Ireland has been based on the LWTBI, although it lies in the western part of this domain. While the original classification was based on manual assessment of weather maps, numerical methods can now be employed to objectively classify a pressure field into a LWT. As a result, it is possible to redefine the region of interest. In this study we applied the objective method to a new domain centred on Ireland (LWTIR). The article compares the catalogue of LWT created for the new domain with that available for the original domain; while the overall synoptic climatology does not change, the sequence of LWT classes differs considerably. As a result, the interpretation of the synoptic origins of precipitation over Ireland is modified and this directs research to new areas of enquiry. This new LWT register that is focused on Ireland provides a more useful context for studying Irish climate and demonstrates the value of the objective method.

A new precipitation and drought climatology based on weather patterns.

ABSTRACTWeather‐pattern, or weather‐type, classifications are a valuable tool in many applications as they characterize the broad‐scale atmospheric circulation over a given region. This study analyses the aspects of regional UK precipitation and meteorological drought climatology with respect to a new set of objectively defined weather patterns. These new patterns are currently being used by the Met Office in several probabilistic forecasting applications driven by ensemble forecasting systems. Weather pattern definitions and daily occurrences are mapped to Lamb weather types (LWTs), and parallels between the two classifications are drawn. Daily precipitation distributions are associated with each weather pattern and LWT. Standardized precipitation index (SPI) and drought severity index (DSI) series are calculated for a range of aggregation periods and seasons. Monthly weather‐pattern frequency anomalies are calculated for SPI wet and dry periods and for the 5% most intense DSI‐based drought months. The new weather‐pattern definitions and daily occurrences largely agree with their respective LWTs, allowing comparison between the two classifications. There is also broad agreement between weather pattern and LWT changes in frequencies. The new data set is shown to be adequate for precipitation‐based analyses in the UK, although a smaller set of clustered weather patterns is not. Furthermore, intra‐pattern precipitation variability is lower in the new classification compared to the LWTs, which is an advantage in this context. Six of the new weather patterns are associated with drought over the entire UK, with several other patterns linked to regional drought. It is demonstrated that the new data set of weather patterns offers a new opportunity for classification‐based analyses in the UK.

The relationship between birch pollen, air pollution and weather types and their effect on antihistamine purchase in two Swedish cities

Exposure to elevated air pollution levels can aggravate pollen allergy symptoms. The aim of this study was to investigate the relationships between airborne birch (Betula) pollen, urban air pollutants NO2, O3 and PM10 and their effects on antihistamine demand in Gothenburg and Malmö, Sweden, 2006–2012. Further, the influence of large-scale weather pattern on pollen-/pollution-related risk, using Lamb weather types (LWTs), was analysed. Daily LWTs were obtained by comparing the atmospheric pressure over a 16-point grid system over southern Sweden (scale ~3000 km). They include two non-directional types, cyclonic (C) and anticyclonic (A) and eight directional types depending on the wind direction (N, NE, E…). Birch pollen levels were exceptionally high under LWTs E and SE in both cities. Furthermore, LWTs with dry and moderately calm meteorological character (A, NE, E, SE) were associated with strongly elevated air pollution (NO2 and PM10) in Gothenburg. For most weather situations in both cities, simultaneously high birch pollen together with high air pollution had larger over-the-counter (OTC) sales of antihistamines than situations with high birch pollen alone. LWTs NE, E, SE and S had the highest OTC sales in both cities. In Gothenburg, the city with a higher load of both birch pollen and air pollution, the higher OTC sales were especially obvious and indicate an increased effect on allergic symptoms from air pollution. Furthermore, Gothenburg LWTs A, NE, E and SE were associated with high pollen and air pollution levels and thus classified as high-risk weather types. In Malmö, corresponding high-risk LWTs were NE, E, SE and S. Furthermore, occurrence of high pollen and air pollutants as well as OTC sales correlated strongly with vapour pressure deficit and temperature in Gothenburg (much less so in Malmö). This provides evidence that the combination of meteorological properties associated with LWTs can explain high levels of birch pollen and air pollution. Our study shows that LWTs represent a useful tool for integrated daily air quality forecasting/warning.

The impact of synoptic weather on UK surface ozone and implications for premature mortality

Air pollutants, such as ozone, have adverse impacts on human health and cause, for example, respiratory and cardiovascular problems. In the United Kingdom (UK), peak surface ozone concentrations typically occur in the spring and summer and are controlled by emission of precursor gases, tropospheric chemistry and local meteorology which can be influenced by large-scale synoptic weather regimes. In this study we composite surface and satellite observations of summer-time (April to September) ozone under different UK atmospheric circulation patterns, as defined by the Lamb weather types. Anticyclonic conditions and easterly flows are shown to significantly enhance ozone concentrations over the UK relative to summer-time average values. Anticyclonic stability and light winds aid the trapping of ozone and its precursor gases near the surface. Easterly flows (NE, E, SE) transport ozone and precursor gases from polluted regions in continental Europe (e.g. the Benelux region) to the UK. Cyclonic conditions and westerly flows, associated with unstable weather, transport ozone from the UK mainland, replacing it with clean maritime (North Atlantic) air masses. Increased cloud cover also likely decrease ozone production rates. We show that the UK Met Office regional air quality model successfully reproduces UK summer-time ozone concentrations and ozone enhancements under anticyclonic and south-easterly conditions for the summer of 2006. By using established ozone exposure-health burden metrics, anticyclonic and easterly condition enhanced surface ozone concentrations pose the greatest public health risk.

Spatial patterns in the oxygen isotope composition of daily rainfall in the British Isles

Understanding the modern day relationship between climate and the oxygen isotopic composition of precipitation (δ18OP) is crucial for obtaining rigorous palaeoclimate reconstructions from a variety of archives. To date, the majority of empirical studies into the meteorological controls over δ18OP rely upon daily, event scale, or monthly time series from individual locations, resulting in uncertainties concerning the representativeness of statistical models and the mechanisms behind those relationships. Here, we take an alternative approach by analysing daily patterns in δ18OP from multiple stations across the British Isles (n = 10–70 stations). We use these data to examine the spatial and seasonal heterogeneity of regression statistics between δ18OP and common predictors (temperature, precipitation amount and the North Atlantic Oscillation index; NAO). Temperature and NAO are poor predictors of daily δ18OP in the British Isles, exhibiting weak and/or inconsistent effects both spatially and between seasons. By contrast δ18OP and rainfall amount consistently correlate at most locations, and for all months analysed, with spatial and temporal variability in the regression coefficients. The maps also allow comparison with daily synoptic weather types, and suggest characteristic δ18OP patterns, particularly associated with Cylonic Lamb Weather Types. Mapping daily δ18OP across the British Isles therefore provides a more coherent picture of the patterns in δ18OP, which will ultimately lead to a better understanding of the climatic controls. These observations are another step forward towards developing a more detailed, mechanistic framework for interpreting stable isotopes in rainfall as a palaeoclimate and hydrological tracer.

A method to assess the inter-annual weather-dependent variability in air pollution concentration and deposition based on weather typing

Annual anomalies in air pollutant concentrations, and deposition (bulk and throughfall) of sulphate, nitrate and ammonium, in the Gothenburg region, south-west Sweden, were correlated with optimized linear combinations of the yearly frequency of Lamb Weather Types (LWTs) to determine the extent to which the year-to-year variation in pollution exposure can be partly explained by weather related variability. Air concentrations of urban NO2, CO, PM10, as well as O3 at both an urban and a rural monitoring site, and the deposition of sulphate, nitrate and ammonium for the period 1997–2010 were included in the analysis. Linear detrending of the time series was performed to estimate trend-independent anomalies. These estimated anomalies were subtracted from observed annual values. Then the statistical significance of temporal trends with and without LWT adjustment was tested. For the pollutants studied, the annual anomaly was well correlated with the annual LWT combination (R2 in the range 0.52–0.90). Some negative (annual average [NO2], ammonia bulk deposition) or positive (average urban [O3]) temporal trends became statistically significant (p < 0.05) when the LWT adjustment was applied. In all the cases but one (NH4 throughfall, for which no temporal trend existed) the significance of temporal trends became stronger with LWT adjustment. For nitrate and ammonium, the LWT based adjustment explained a larger fraction of the inter-annual variation for bulk deposition than for throughfall. This is probably linked to the longer time scale of canopy related dry deposition processes influencing throughfall being explained to a lesser extent by LWTs than the meteorological factors controlling bulk deposition. The proposed novel methodology can be used by authorities responsible for air pollution management, and by researchers studying temporal trends in pollution, to evaluate e.g. the relative importance of changes in emissions and weather variability in annual air pollution exposure.

The influence of synoptic weather regimes on UK air quality: regional model studies of tropospheric column NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Abstract. Synoptic meteorology can have a significant influence on UK air quality. Cyclonic conditions lead to the dispersion of air pollutants away from source regions, while anticyclonic conditions lead to their accumulation over source regions. Meteorology also modifies atmospheric chemistry processes such as photolysis and wet deposition. Previous studies have shown a relationship between observed satellite tropospheric column NO2 and synoptic meteorology in different seasons. Here, we test whether the UK Met Office Air Quality in the Unified Model (AQUM) can reproduce these observations and then use the model to explore the relative importance of various factors. We show that AQUM successfully captures the observed relationships when sampled under the Lamb weather types, an objective classification of midday UK circulation patterns. By using a range of idealized NOx-like tracers with different e-folding lifetimes, we show that under different synoptic regimes the NO2 lifetime in AQUM is approximately 6 h in summer and 12 h in winter. The longer lifetime can explain why synoptic spatial tropospheric column NO2 variations are more significant in winter compared to summer, due to less NO2 photochemical loss. We also show that cyclonic conditions have more seasonality in tropospheric column NO2 than anticyclonic conditions as they result in more extreme spatial departures from the wintertime seasonal average. Within a season (summer or winter) under different synoptic regimes, a large proportion of the spatial pattern in the UK tropospheric column NO2 field can be explained by the idealized model tracers, showing that transport is an important factor in governing the variability of UK air quality on seasonal synoptic timescales.

Long‐term trends in gale days and storminess for the Falkland Islands

ABSTRACTWeather typing, based on surface pressure charts, has been one of the principal means of analysis in synoptic climatology. Here, we use an automated scheme to derive weather types (WTs) and also calculate Lamb weather types (LWTs) for the Falkland Islands. The WTs are based on sea‐level pressure data estimated using two reanalysis products: one that extends from 1948 to 2014 and another that just uses station pressure data as input and extends back to 1871. The WTs can be used to derive counts of gale days and these will be compared with storminess estimates based on the rate of change of daily‐average pressure measurements at the principal observational site (near the capital, Port Stanley) on the islands. A particular emphasis of the paper is the reliability of the results taking into account that we are using reanalysis datasets from a very data‐sparse region of the world. More gale days are estimated during the period from about 1880 to the mid‐1910s and since the 1980s. Fewer gale days are evident during other periods, particularly from the mid‐1910s to 1947. As these changes are not evident in the storminess measure derived from the sub‐daily pressure series for the Port Stanley region, the results in terms of gale‐day counts are very suggestive of being due to differences in the quality of the reanalysis during the different periods. The reanalysis appears better the higher the number of gale days estimated. The opening of the Panama Canal in 1914 dramatically reduced the number of ships, and hence observations, rounding Cape Horn. The paper also relates seasonal counts of the LWTs and WTs to recently developed long series of temperature and precipitation for the Port Stanley region.

Influence of atmospheric circulation patterns on urban air quality during the winter

Relationships between urban nitrogen dioxide (NO2) and atmospheric circulation at two spatial scales were studied for Southern Sweden. Lamb Weather Types (LWT) describe the circulation (scale: thousands of kilometers) including non–directional (cyclonic and anticyclonic) and directional types depending on the wind direction. LWTs with low wind speeds (anticyclonic, NW and N) were associated with strongly elevated [NO2], between 46–52% of the daily averages of NO2 exceeded the 60μg m−3 air quality standard (AQS) when occurring during these LWTs. The lowest fractions of exceedances of NO2 AQS were generally observed for LWTs E, S, SW and W. A larger scale circulation (several thousands of kilometers) was represented by the North Atlantic Oscillation (NAO) affecting meteorology over middle and high latitudes in the Northern Hemisphere. While a negative NAO index (NAOI) favors stagnant high pressure weather over Northern Europe, a positive NAOI is often associated with windy conditions. High [NO2] was found to be frequent under negative NAOI. Additionally, larger fractions of exceedances of NO2 AQS were observed for the majority of LWTs occurring at negative NAOI. It’s concluded that both LWTs and NAOI had partly independent effects on the urban air quality in a North European city. These circulation indices can be useful tools for air pollution risk assessment and forecasting.

Atmospheric circulation types in Marmara Region (NW Turkey) and their influence on precipitation

ABSTRACTIn this study, circulation types, their long‐term mean occurrence frequencies and relationships with precipitation are investigated for the region Marmara, which is the most populated, agriculturally developed and industrialized area in Turkey. Automated Lamb Weather Types classification method is applied on NCEP/NCAR daily mean sea level pressure data to determine the circulation types. Northeasterly (NE) and easterly (E) types are found to be the most frequent both on the annual basis and during winter (DJF, the wettest season in the region). Circulation types with the highest rainfall potential, namely the cyclonic (C) and the northerly (N), are among the least frequent; therefore they are not the dominant ‘rainfall modes’. Instead, NE and E have the greatest contribution to the regionally averaged rainfall amount, although they do not have the highest potential to create precipitation. This shows that Marmara Region receives a substantial amount of precipitation from northerly and easterly maritime trajectories, implying a profound influence of the Black Sea on the rainfall regime in this area. However, rainfall at the stations that are far away or less affected by the Black Sea (especially at the ones in the west) occurs during types with a southerly component (S, SW and SE). Our results reveal that, in Marmara Region, the response of precipitation to atmospheric circulation is rather complex and spatially inhomogeneous; in line with the complex topography of the area. Therefore, water management policies should be adopted accordingly, taking all local characteristics into account.

Birmingham’s air and surface urban heat islands associated with Lamb weather types and cloudless anticyclonic conditions

This study investigates the characteristics of the air and surface urban heat islands (aUHI and sUHI) of Birmingham in relation to Lamb weather types (LWTs) over the period 2002–2007, with a particular focus on cloudless anticyclonic conditions. Ground-based MIDAS air temperatures within the urban canopy layer at the urban Edgbaston and rural Shawbury weather stations were used to derive the aUHI intensity (aUHII). Satellite-derived MODIS/Aqua land surface temperatures (LST) under cloudless conditions were used to derive the spatial patterns of the sUHI as well as the sUHI intensity (sUHII). Using Jenkinson’s objective daily synoptic indices, a combined subset of 11 LWTs were examined for their association with the nocturnal aUHI. Over the study period, the most frequently occurring LWT, ‘anticyclonic’ (21.1%), gives a strongest mean/maximum nocturnal aUHII of 2.5°C/7°C (391 nights) and the largest proportion of nocturnal heat island events of 65.2%. The spatial patterns of nocturnal sUHI for each LWT were also assessed, and the results demonstrate Birmingham’s urban warming of up to 4.16°C (48 clear nights) in the city centre under cloudless anticyclonic conditions. The scatter plot of nocturnal aUHII and sUHII for the 48 nights demonstrates a linear relationship. We also developed a simple analytical model that links the slope of the aUHII–sUHII relationship to the difference of ‘built-up’ area fraction between the urban pixel and the rural pixel in satellite imagery of land cover. This partially explains the physical basis behind the relationship. These findings of the aUHII–sUHII relationship may lead to the future development of a generic methodology of deriving the spatial patterns of aUHI from satellite measurements.

The development of Lamb weather types: from subjective analysis of weather charts to objective approaches using reanalyses

The development of Lamb weather types: from subjective analysis of weather charts to objective approaches using reanalyses