Lamb Weather Types Research Articles

A coupled synoptic-hydrological model for climate change impact assessment

A coupled atmospheric-hydrological model is presented. Sequences of daily rainfall occurrence for the 20 year period 1971–1990 at sites in the British Isles are related to the Lamb's Weather Types (LWT) by using conditional probabilities. Time series of circulation patterns and hence rainfall were then generated using a Markov representation of matrices of transition probabilities between weather types. The resultant precipitation data were used as input to a semidistributed catchment model to simulate daily flows. The combined model successfully reproduced aspects of the daily weather, precipitation and flow regimes. A range of synoptic scenarios were further investigated with particular reference to low flows in the River Coln, UK. The modelling approach represents a means of translating general circulation model (GCM) climate change predictions at the macro-scale into hydrological concerns at the catchment scale.

A comparison of Lamb circulation types with an objective classification scheme

AbstractAn objective scheme, initially developed by Jenkinson and Collison, is used to classify daily circulation types over the British Isles, along the lines of the subjective method devised by Lamb. The scheme uses daily grid‐point mean sea‐level pressure data for the region. The results of the analysis over the period 1881–1989 are compared with ‘true’ Lamb weather types. The frequencies of objectively developed types are highly correlated with traditional Lamb types, especially so for synoptic (cyclonic and anticyclonic) types, although still good for wind directional types. Comparison of the two classification schemes reveals negligible differences between the correlations of the counts of circulation types and regional temperature and rainfall. The major difference between the two classification schemes is that the decline of the westerlies since 1940 is less evident with the objective scheme.

The meteorological control on the anthropogenic ion content of precipitation at three sites in the UK: The utility of lamb weather types

AbstractDaily observations of concentrations of non‐marine sulphate, nitrate, ammonium, and hydrogen ion in precipitation at three sites in the UK (south‐west England, eastern England, southern Scotland) have been used to attribute proportions of the total annual depositions of these ions to various Lamb Weather Types (LWTs). The LWT classification is a convenient description of the daily atmospheric circulation over the British Isles. In terms of affecting the annual character of total annual deposition of the ions, it is Cyclonic, Westerly, and Anticyclonic weather types that play the dominant roles. These roles vary from station to station. Other LWTs can also play important roles, but there is much site‐to‐site and year‐to‐year variation. The patterns of the relationships for each of the stations are explained in terms of the ‘average’ back‐trajectories from each station for precipitation events associated with each of the major LWTs. It is the relative dispositions of these average trajectories with respect to the major pollutant source regions that allows the use of LWTs as simple tools in the interpretation of precipitation composition. There are indications that atmospheric circulation changes may play a part in the variations of precipitation composition over years to decades.