On the Potential of 25 Years (1991–2015) of Rawinsonde Measurements for Elucidating Climatological and Spatiotemporal Patterns of Afternoon Boundary Layer Depths over the Contiguous US

Abstract

The daytime planetary boundary layer (PBL) depth is an essential parameter in, for example, dispersion models and numerical weather prediction. We applied a recently developed technique to estimate afternoon PBL depths from 516,887 daily rawinsonde measurements obtained at 0000 UTC between 1 Jan 1991 and 31 Dec 2015 from 67 US sites. We discuss salient features in the PBL depth variability and examine the climatology of afternoon PBL depths as a function of geographical region and Köppen-Geiger climate regime. Results indicated a strong east to west PBL depth gradient, with higher PBL depths over the semiarid regions of the western US in spring and summer. Many sites located near coastlines exhibited no seasonal cycle due to marine boundary layer influences, and an inverse relationship was found between distance from the coast and observed afternoon PBL depth. Differentiating by climate type, BWk (arid, desert, and cold) has the largest median winter (1075 m) and summer (2500 m) PBL depths. Median PBL depths for Cfa (temperate, no dry season, and hot summers), Dfa (cold, no dry season, and warm summer), and Dfb (cold, no dry season, and hot summers) climate types are 750 m and 1000 m during winter and summer, respectively.

Contrasting Air Mass Advection Explains Significant Differences in Boundary Layer Depth Seasonal Cycles Under Onshore Versus Offshore Flows

“…For instance, the mean summertime precipitation over 1981–2010 was 5.9 cm, and year‐to‐year variability was extreme with a drift of summer precipitation of around −5‐4 cm. Deep ABL in summer over such climatic regions in the United States are not unusual, as reported in previous studies (Lee & Pal, ; Seidel et al, ). Both rawinsonde sites at San Diego and Oakland are characterized by urban hotspots which likely trigger high summer time BLDs under offshore flow.…”

The 2019 Mississippi and Missouri River Flooding and Its Impact on Atmospheric Boundary Layer Dynamics

“…We estimated the daily afternoon BLDs from the 00 UTC soundings over the 10 sites (Figure 1a) using a recently developed method based on the analyses of bulk Richardson number ( Ri b ) (Koffi et al, 2016; Lee & De Wekker, 2016; Lee & Pal, 2017). From the profile of Ri b , we estimated the ABL top as the height at which the Ri b first exceeded 0.25 (e.g., Vogelezang & Holtslag, 1996).…”

Advected Air Mass Reservoirs in the Downwind of Mountains and Their Roles in Overrunning Boundary Layer Depths Over the Plains

“…Previously, a number of studies (Carlson & Ludlam, ; Lanicci & Warner, ) found the elevated terrains of Mexico to be one of the major sources of EMLs; these potentially warm EMLs also were found to have a northward expansion into the Rocky Mountains. Figure b suggests relatively deeper (>2,500 m AGL) over the R5 sites (Midland, Santa Teresa, and Del Rio) compared to the other sites in the Southern Great Plains, which could be attributed to the ABL features over dry warm arid regions like the southwest United States (Lee & Pal, ).…”

“…Using an improved version of the bulk Richardson number (R ib ) approach (Lee & De Wekker, 2016;Lee & Pal, 2017), we computed the daily afternoon BLDs from the 00 UTC soundings available from the Integrated Global Radiosonde Archive (IGRA; Durre et al, 2006) for 22 sites (Figure 1). We determined the top of the ABL as the height at which the R ib first exceeded 0.25 (e.g., Seidel et al, 2010Seidel et al, , 2012Vogelezang & Holtslag, 1996).…”

“…We classified the IGRA sites into two broad categories: R and A sites located in the downstream of Rocky and Appalachian Mountains, respectively. We further classified the R sites among five subcategories (R1, R2, R3, R4, and R5) and the A sites into four subcategories (A0, A1, A2, and A3) depending on the regions and latitudinal spans and broad geographical regions (Figure ), as discussed in Lee and Pal ().…”