TY - JOUR

T1 - Cold pools over the Netherlands

T2 - A statistical study from tower and radar observations

AU - Kruse, Irene L.

AU - Härter, Jan Olaf Mirko

AU - Meyer, Bettina

PY - 2021/12/27

Y1 - 2021/12/27

N2 - We provide a detailed analysis of convectively generated cold pools (CPs) over flat midlatitude land, combining ten-year high-frequency time series of measurements at several heights available from the 213-m tower observatory at Cabauw, the Netherlands, with a collocated 2D radar rainfall dataset. This combination of data allows us to relate observations of the CP's temporal and vertical structure to the properties of each CP's parent rain cell, which we identify by rain-cell tracking. Using a new detection method, based on the anomalies of both the vertically averaged wind and the temperature, we monitor the arrival and passing of 189 CPs during ten summers (2010-2019). The time series show a clear signature of vortex-like motion along the leading CP edge in the vertical and horizontal wind measurements. The arrival of CP gust fronts is characterized by a steep decrease in both temperature and moisture, with a recovery time of approximately two hours. We see no evidence of moisture rings on the gust front edge, and therefore no indications for thermodynamic convective triggering. From the tower data, we obtain a median CP temperature drop of Tdrop approximate to-2.9 K and a height-averaged horizontal wind anomaly of Delta umax approximate to 4.4 m center dot s-1. Relating the individual CP's horizontal wind anomalies and temperature drops, we confirm the validity of the theoretical density current relationship, Delta umax proportional to Tdrop1/2. We further propose a simple statistical model to relate the CP strength defined by Tdrop to the environmental properties influencing the CP: rain intensity and lower boundary-layer saturation. A multivariate linear regression suggests a 1 K colder CP for a 4 mm center dot hr-1 more intense rain cell (instantaneous area-averaged rain intensity) or for a 2.5 K larger pre-CP dew-point depression.

AB - We provide a detailed analysis of convectively generated cold pools (CPs) over flat midlatitude land, combining ten-year high-frequency time series of measurements at several heights available from the 213-m tower observatory at Cabauw, the Netherlands, with a collocated 2D radar rainfall dataset. This combination of data allows us to relate observations of the CP's temporal and vertical structure to the properties of each CP's parent rain cell, which we identify by rain-cell tracking. Using a new detection method, based on the anomalies of both the vertically averaged wind and the temperature, we monitor the arrival and passing of 189 CPs during ten summers (2010-2019). The time series show a clear signature of vortex-like motion along the leading CP edge in the vertical and horizontal wind measurements. The arrival of CP gust fronts is characterized by a steep decrease in both temperature and moisture, with a recovery time of approximately two hours. We see no evidence of moisture rings on the gust front edge, and therefore no indications for thermodynamic convective triggering. From the tower data, we obtain a median CP temperature drop of Tdrop approximate to-2.9 K and a height-averaged horizontal wind anomaly of Delta umax approximate to 4.4 m center dot s-1. Relating the individual CP's horizontal wind anomalies and temperature drops, we confirm the validity of the theoretical density current relationship, Delta umax proportional to Tdrop1/2. We further propose a simple statistical model to relate the CP strength defined by Tdrop to the environmental properties influencing the CP: rain intensity and lower boundary-layer saturation. A multivariate linear regression suggests a 1 K colder CP for a 4 mm center dot hr-1 more intense rain cell (instantaneous area-averaged rain intensity) or for a 2.5 K larger pre-CP dew-point depression.

KW - atmospheric convection

KW - cold pools

KW - convective downdrafts

KW - INTERACTING THUNDERSTORM OUTFLOWS

KW - VERTICAL WIND SHEARS

KW - TROPICAL CONVECTION

KW - GUST FRONTS

KW - MESOSCALE

KW - ORGANIZATION

KW - CONVERGENCE

KW - SIMULATION

KW - INITIATION

KW - EVOLUTION

U2 - 10.1002/qj.4223

DO - 10.1002/qj.4223

M3 - Journal article

VL - 148

SP - 711

EP - 726

JO - Quarterly Journal of the Royal Meteorological Society

JF - Quarterly Journal of the Royal Meteorological Society

SN - 0035-9009

IS - 743

ER -