Measurement and modelling of temperature cold pools in the Cerdanya valley (Pyrenees), Spain

Abstract

The Cerdanya valley in northeast Spain 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 Conflent 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 December 2012 and January 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 Cerdanya and mountain valleys elsewhere.

Estimation of near‐surface air temperature lapse rates over continental Spain and its mountain areas

“…This behaviour might be due to the persistence of snow cover at highest stations in winter and, occasionally, in spring due to heat exchange and albedo as previously proposed by Rolland (), Pepin and Kidd (), or Pagès et al . (). In the mountain area nearest to the ocean (the Cantabrian range), the weakest NSLR d mean occurred in summer.…”

Synoptic‐flow interaction with valley cold‐air pools and effects on cold‐air pool persistence: Influence of valley size and atmospheric stability

“…; Largeron and Staquet, ), the Pyrenees (Pages et al . ), and ranges of large mountains in the Middle East (Crosbie et al . ; Khokhar et al .…”

“…; Pages et al . ). Persistent CAPs in urbanized or industrialized areas have serious implications for accumulation of pollution and it is important to understand how and why this transition from small, diurnal CAPs to large, persistent CAPs occurs as a function of increasing scale and atmospheric conditions.…”

Key features of cold‐air pool episodes in the northeast of the Iberian Peninsula (Cerdanya, eastern Pyrenees)

“…Sensors were placed into white polyvinyl chloride (PVC) pipes 30–40 cm long and 15 cm wide (Pagès et al, ) to protect from direct radiation, yet still allow ventilation (Figure ). Trees (36 cases) or other permanent fixtures (four cases) were used and the sensor installed at 1.5 m above the ground.…”

“…Most trees were evergreen, either pine ( Pinus halepensis and Pinus sylvestris ) or juniper ( Juniperus phoenicea ). Although trees can create their own microclimate, large parts of the study area are forested so trees have a strong influence on the broader climate (Pagès et al, ).…”