Uncertainty in Estimating Boundary-Layer Transport during Highly Convective Conditions

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  • 1 Department of Atmospheric and Oceanic Science, Space Physics Research Laboratory, University of Michigan, Ann Arbor, Michigan
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Abstract

Routine and supplemental rawinsonde observations collected during the Preliminary Regional Experiment for Storm-Central (PRE-STORM) were analyzed to assess the uncertainty in boundary-layer trajectory calculations due to imprecise interpolation of the horizontal wind field. This study was designed to complement our earlier analysis of rawinsonde data collected during the Cross Appalachian Tracer Experiment (CAPTEX; Kahl and Samson 1986). The present study is representative of widespread convective conditions, while our previous study was representative of fairly persistent, undisturbed flow.

Spatial autocorrelation analysis revealed significant wind field variability on scales less than 100 km. Evaluation of several spatial and temporal interpolation techniques yielded mean absolute errors in estimation of u and v wind components ranging from 3.3–6.5 m −1. Spatial interpolation accuracy improved only slightly when supplemental measurements were included in the interpolation procedure.

Estimates of trajectory errors were obtained using the “trajectory of errors” model of Kahl and Samson (1986). Mean horizontal errors of 493 km were found after 72 h of travel. Contributions of spatial and temporal interpolation to the overall trajectory error were equivalent. Trajectory errors wore 40% greater than those estimated using CAPTEX interpolation statistics.

The presence of predominant mesoscale circulations during PRE-STORM is responsible for the elevated small-scale wind variability as compared to CAPTEX conditions, thus leading to larger interpolation errors and, in turn, larger trajectory errors. Our results suggest that data resolution finer than that considered in this study is necessary to significantly improve trajectory accuracy during meteorological conditions similar to PRE-STORM.

Abstract

Routine and supplemental rawinsonde observations collected during the Preliminary Regional Experiment for Storm-Central (PRE-STORM) were analyzed to assess the uncertainty in boundary-layer trajectory calculations due to imprecise interpolation of the horizontal wind field. This study was designed to complement our earlier analysis of rawinsonde data collected during the Cross Appalachian Tracer Experiment (CAPTEX; Kahl and Samson 1986). The present study is representative of widespread convective conditions, while our previous study was representative of fairly persistent, undisturbed flow.

Spatial autocorrelation analysis revealed significant wind field variability on scales less than 100 km. Evaluation of several spatial and temporal interpolation techniques yielded mean absolute errors in estimation of u and v wind components ranging from 3.3–6.5 m −1. Spatial interpolation accuracy improved only slightly when supplemental measurements were included in the interpolation procedure.

Estimates of trajectory errors were obtained using the “trajectory of errors” model of Kahl and Samson (1986). Mean horizontal errors of 493 km were found after 72 h of travel. Contributions of spatial and temporal interpolation to the overall trajectory error were equivalent. Trajectory errors wore 40% greater than those estimated using CAPTEX interpolation statistics.

The presence of predominant mesoscale circulations during PRE-STORM is responsible for the elevated small-scale wind variability as compared to CAPTEX conditions, thus leading to larger interpolation errors and, in turn, larger trajectory errors. Our results suggest that data resolution finer than that considered in this study is necessary to significantly improve trajectory accuracy during meteorological conditions similar to PRE-STORM.

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