Measurement methods validation: adequacy and validation of meteorological measurements aloft during IMS95


[Click here to download the entire report (zipped Microsoft Word files in ~709 kb)]

The overall objectives of Task 4.1.2 are to evaluate the validity of the meteorological data collected during IMS95 and assess the adequacy of the IMS95 meteorological data set for the purposes of meteorological analyses. To achieve these objectives, we identified the operational performance of each measurement system including its accuracy and precision, evaluated the Radio Acoustic Sounding System (RASS) data to determine whether a cold bias exists, and evaluated the quality of the Cn2- and the RASS-derived mixing depth estimates. We also investigated the adequacy of surface and aloft meteorological wind measurements to characterize transport conditions, and identified methods to estimate temperature from virtual temperature measurements and to quantify the uncertainty in using the estimated values.

The technical approach to evaluate the validity of the IMS95 meteorological data set is broken into five steps: (1) literature survey, (2) analyze the effects of a cold bias in RASS Tv measurements, (3) determine uncertainties in RWP estimates of the mixed layer, (4) evaluate potential transport analyses, and (5) evaluate methods to convert virtual temperature to temperature.

In this report each of the five technical tasks is reported as a separate volume. These tasks and their major findings are as follows:

  1. Results of a Literature Search to Evaluate the Performance of Upper-Air Measurement Systems


  • A sufficient number of intercomparison results have demonstrated that these upper-air systems produce routinely reliable data


  1.   Evaluation of Mixing Depths Computed from Radar Wind Profilers and Radio Acoustic Sounding Systems


  • Comparison of mixing depths derived from radar profiler and rawinsonde data show good agreement and virtually no bias even though the upper-air sites were not collocated, but separated by 20 km.


  • The hourly Cn2/RASS data were able to portray the location and evolution of aloft layers with more detail than the 6-hour rawinsonde data.


  1.   Evaluation of a Potential Cold Bias in the Radio Acoustic Sounding System (RASS) Virtual Temperatures Collected During the IMS95 Study


  • Analyses using different comparison techniques showed that no cold bias was observed in the RASS virtual temperature data.


  1.   Methods to Estimate Temperature from Virtual Temperature Collected from Radio Acoustic Sounding Systems (RASS)


  • Two methods were identified to estimate temperature from RASS virtual temperature measurements.


  • Evaluation against rawinsonde temperature data showed errors in the RASS temperature estimates ranging from 0 to 0.6 C depending upon the method used.


  1. Transport Analyses Using Data from Radar Wind Profiler and Rawinsonde Systems


  • The upper-air data revealed a pronounced vertical layer and three distinct wind regimes:
    • Surface up to around 1000 m agl
    • 1000 m agl to 2000 m agl
    • Above 2000 m agl
  • Surface winds were only representative of a shallow layer of aloft winds and were better correlated with aloft winds at sites farther from complex terrain.
  • Transport statistics from the continuous (hourly) radar profiler data and intermittent rawinsonde data were comparable under moderate wind condition, but had large differences during light and very strong winds (due to inhomogeneities in the winds between the upper-air sites).


[Click here to download the entire report (zipped Microsoft Word files in ~709 kb)]