Measurement and modelling of temperature cold pools in the <scp>C</scp>erdanya valley (Pyrenees), Spain

Abstract

ABSTRACT The C erdanya valley in northeast S pain experiences intense cold air pooling which decouples the valley atmosphere from the regional circulation, especially in winter. This makes air temperature prediction a challenge. A network of 40 temperature sensors was installed in 2012 along seven elevational transects to collect hourly temperatures throughout the cold pool, enabling measurement of the detailed cold pool structure for the first time. Sensors were also installed in the upper C onflent valley to the northeast for comparison, where previous research has shown that there is reduced cold air pooling. Sensor data were validated against automatic weather station observations at two locations. Through calculation of hourly lapse rates in various elevation bands for 2 years, frequent inversions developing up to 1450 m are shown, and sometimes extending much higher than this, concentrating in winter. Case studies of two intense episodes in D ecember 2012 and J anuary 2013 show that model simulations, despite being able to simulate broad mechanisms of cold air pooling formation, underestimate the amount of cooling. This is due to over‐enthusiastic simulation of a low level jet in the first case and mountain waves in the second. Solving these model problems has important consequences for the future ability to predict episodes of extreme low temperatures and associated hazards (frost, fog) in C erdanya and mountain valleys elsewhere.