The characteristics of atmospheric boundary layer height over the Arctic Ocean during MOSAiC

Abstract

Abstract. The important roles that the atmospheric boundary layer (ABL) plays in the central Arctic climate system have been recognized, but the atmospheric boundary layer height (ABLH), defined as the layer of continuous turbulence adjacent to the surface, has rarely been investigated. Using a year-round radiosonde dataset during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we improve a Richardson-number-based algorithm that takes cloud effects into consideration and subsequently analyze the characteristics and variability of the ABLH over the Arctic Ocean. The results reveal that the annual cycle is clearly characterized by a distinct peak in May and two respective minima in January and July. This annual variation in the ABLH is primarily controlled by the evolution of the ABL thermal structure. Temperature inversions in the winter and summer are intensified by seasonal radiative cooling and warm-air advection with the surface temperature constrained by melting, respectively, leading to the low ABLH at these times. Meteorological and turbulence variables also play a significant role in ABLH variation, including the near-surface potential temperature gradient, friction velocity, and turbulent kinetic energy (TKE) dissipation rate. In addition, the MOSAiC ABLH is more suppressed than the ABLH during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment in the summer, which indicates that there is large variability in the Arctic ABL structure during the summer melting season.

The Role of Non‐Local Effects on Surface Sensible Heat Flux Under Different Types of Thermal Structures Over the Arctic Sea‐Ice Surface

“…The increase of strong surface inversions during winter may be due to the radiative cooling of the sea‐ice surface combined with relatively warm air advection aloft. The formation of strong surface inversions in summer can be attributed to the significant increase in air temperature coupled with the melting surface's constrained temperature (∼0°C) (Peng et al., 2023).…”

“…In this study, the determination of h i follows Peng et al. (2023). To analyze the dependence of the surface scaling on Fi, Equation can be rewritten as follows: $$${s}_{\theta }=\frac{{k}_{T}L}{{\theta }_{\ast }}\frac{\partial \theta }{\partial z}-\frac{L}{z}={C}_{\theta 1}{\left(1+{C}_{\theta 2}\text{Fi}\right)}^{2}.$$$ …”

“…Here, C θ2 is a dimensionless coefficient; Fi is the inverse Froude number (higher values of Fi indicate more significant contributions from non-local transport); N is the Brunt-Väisälä frequency; and h i is the ABL height. In this study, the determination of h i follows Peng et al (2023). To analyze the dependence of the surface scaling on Fi, Equation 7 can be rewritten as follows:…”

On the Mechanisms Driving Latent Heat Flux Variations in the Northwest Tropical Atlantic

“…Before calculating the MABLH, we first perform a linear interpolation to all vertical profiles to fill in missing values. Then, we smooth the air temperature, winds, and surface water vapor mixing ratio using a five-point running average (equivalent to 50 m in height) as in Hande et al (2012) or Peng et al (2023). We perform this operation to remove small scale features in the vertical profiles that could lead to spurious MABLH values.…”

Evaluation of the Planetary Boundary Layer Height From ERA5 Reanalysis With MOSAiC Observations Over the Arctic Ocean

“…Here, we set g as 9.8 m s 2 , U s and V s as zero, C p as 1004.7 J kg 1 K 1 , R vap as 465.1 J kg 1 K 1 , R dry as 287.05 J kg 1 K 1 , and ε as 0.61. Notably, we only considered PBLH values between 20 and 1,200 m, which represents a reasonable range for PBLH in this region (Jozef et al, 2022;Peng et al, 2023) to ensure the reliability and accuracy of our data set (available numbers = 1,318). Data not within this range are manually excluded, including 2 cases falling below 20 m and a total of 3 cases exceeding 1,200 m.…”