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Both the figures reveal the complex aerosol and cloud structure occurring during the period under consideration (16-21 October 2022), which is characterized by highly vari- able meteorological conditions. More specifically, several aerosol and humidity layers are present at different altitudes, as well as water and mixed-phase clouds. The characterization of the ABL height in such complex weather conditions is particularly challenging and, in general, is affected by large uncertainties. In previous studies from the same and other au- hors, it was demonstrated that the characterization of the ABLH can be effectively pursued by combining observations made by different sensors and different methodological re- rieval approaches. The weather conditions occurring during the considered measurement period result from the deepening of a large low-pressure system over Spain and Portuga and the associated cold front. A low-altitude flow is present over the Mediterranean Sea, which brings warm, humid air and persistent orographic rainfall events to the CV area. On 19 October, the isolated low-pressure system in the southern part of the elongated depression area near Portugal began moving northeast from Morocco to Murcia. An event of high rainfall hit eastern Spain on that day [51].

Figure 1 Both the figures reveal the complex aerosol and cloud structure occurring during the period under consideration (16-21 October 2022), which is characterized by highly vari- able meteorological conditions. More specifically, several aerosol and humidity layers are present at different altitudes, as well as water and mixed-phase clouds. The characterization of the ABL height in such complex weather conditions is particularly challenging and, in general, is affected by large uncertainties. In previous studies from the same and other au- hors, it was demonstrated that the characterization of the ABLH can be effectively pursued by combining observations made by different sensors and different methodological re- rieval approaches. The weather conditions occurring during the considered measurement period result from the deepening of a large low-pressure system over Spain and Portuga and the associated cold front. A low-altitude flow is present over the Mediterranean Sea, which brings warm, humid air and persistent orographic rainfall events to the CV area. On 19 October, the isolated low-pressure system in the southern part of the elongated depression area near Portugal began moving northeast from Morocco to Murcia. An event of high rainfall hit eastern Spain on that day [51].

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Table 1. Summary of the considered instruments /approaches used to determine the ABLH.
Table 1. Summary of the considered instruments /approaches used to determine the ABLH.
These complex weather conditions are well suited to test the different sensors /models / approaches and their performance. As already specified above, different approaches have been considered for the determination of the ABLH. In all the cases, ABLH estimates come from signal profiles with a vertical and time resolution of 30 m and 5 min, respectively. Figure 2 illustrates the evolution of the ABLH estimated through the different approaches. n general, the overall agreement is good, with an increasing trend of the ABLH until the central part of the day on 18 October, an abrupt decrease during the second part of the same day and the morning of 19 October, an abrupt new increase during the central part of he day on 19 October, and a final progressive decrease late on 20-21 October. The abrupt increase revealed through all the compared approaches on 19 October is most probably due o a sudden increase in the main motor friction coefficient of the ABL [52-54]. Figure 2. Comparison of ABLH estimated using different methods with reference values obtained from the temperature gradient technique applied to on-site radiosonde data (green stars) during the period from 16-21 October 2012.
These complex weather conditions are well suited to test the different sensors /models / approaches and their performance. As already specified above, different approaches have been considered for the determination of the ABLH. In all the cases, ABLH estimates come from signal profiles with a vertical and time resolution of 30 m and 5 min, respectively. Figure 2 illustrates the evolution of the ABLH estimated through the different approaches. n general, the overall agreement is good, with an increasing trend of the ABLH until the central part of the day on 18 October, an abrupt decrease during the second part of the same day and the morning of 19 October, an abrupt new increase during the central part of he day on 19 October, and a final progressive decrease late on 20-21 October. The abrupt increase revealed through all the compared approaches on 19 October is most probably due o a sudden increase in the main motor friction coefficient of the ABL [52-54]. Figure 2. Comparison of ABLH estimated using different methods with reference values obtained from the temperature gradient technique applied to on-site radiosonde data (green stars) during the period from 16-21 October 2012.
Table 2. Statistical analysis, considering relative biases, of the ABLH estimates obtained with the different approaches/sensors. The linear fitting (Y = A - X) of the compared approaches versus radiosondes (on site) is also reported. Values reported in Table 2 are also illustrated in Figures 3 and 4, where the relative bias (%) and scatter plot of all the compared approaches against radiosondes are reported. These figures clearly reveal that MIPA, which is the only approach based uniquely on RCSs, provides effective ABLH estimates in the time interval 18-20 October 2012, with a mutual bias with respect to the reference of 4-8% in correspondence of the two selected stable sub-intervals, while larger deviations are found on 16-17 and 21 October 2012 (unstable conditions), with values as large as —11.24% and +12.89%, respectively. The approaches that seem to be more accurate during stable conditions are those based on the application of the derivative algorithm to x420(z) and to the logarithm of the rotational signal ratio Pyiy(z) /Ptoj(z), with relative bias values smaller than 7.24% and 7.72%, respectively. A possible explanation for such behavior could be the enhanced aerosol deposition (within the ABL) occurring under unstable weather conditions. The lower aerosol concentration in the ABL could explain the larger deviations produced by MIPA, which is the only algorithm working on the elastic RCS. The water vapor content is expected to be less affected by deposition processes, while the methodology based on the pure rotational Raman signals is not affected at all because it works on molecular targets. a Pron — ae Pe ere eed Table 2. Statistical analysis, considering relative biases, of the ABLH estimates obtained with the
Table 2. Statistical analysis, considering relative biases, of the ABLH estimates obtained with the different approaches/sensors. The linear fitting (Y = A - X) of the compared approaches versus radiosondes (on site) is also reported. Values reported in Table 2 are also illustrated in Figures 3 and 4, where the relative bias (%) and scatter plot of all the compared approaches against radiosondes are reported. These figures clearly reveal that MIPA, which is the only approach based uniquely on RCSs, provides effective ABLH estimates in the time interval 18-20 October 2012, with a mutual bias with respect to the reference of 4-8% in correspondence of the two selected stable sub-intervals, while larger deviations are found on 16-17 and 21 October 2012 (unstable conditions), with values as large as —11.24% and +12.89%, respectively. The approaches that seem to be more accurate during stable conditions are those based on the application of the derivative algorithm to x420(z) and to the logarithm of the rotational signal ratio Pyiy(z) /Ptoj(z), with relative bias values smaller than 7.24% and 7.72%, respectively. A possible explanation for such behavior could be the enhanced aerosol deposition (within the ABL) occurring under unstable weather conditions. The lower aerosol concentration in the ABL could explain the larger deviations produced by MIPA, which is the only algorithm working on the elastic RCS. The water vapor content is expected to be less affected by deposition processes, while the methodology based on the pure rotational Raman signals is not affected at all because it works on molecular targets. a Pron — ae Pe ere eed Table 2. Statistical analysis, considering relative biases, of the ABLH estimates obtained with the
Figure 3. Relative biases (%) of the ABLH estimates obtained by the compared methods with respect to reference data during the period 16-21 October 2012.
Figure 3. Relative biases (%) of the ABLH estimates obtained by the compared methods with respect to reference data during the period 16-21 October 2012.
Figure 4. Comparison of different ABLH estimates expressed in terms of linear fitting for each approach. The x-axis shows the ABLH reference values obtained by applying the potential tem- erature approach to in-situ radiosondes, while the y-axis refers to the estimates provided by the compared approaches. ‘igure 4. Comparison of different ABLH estimates expressed in terms of linear fitting for each
Figure 4. Comparison of different ABLH estimates expressed in terms of linear fitting for each approach. The x-axis shows the ABLH reference values obtained by applying the potential tem- erature approach to in-situ radiosondes, while the y-axis refers to the estimates provided by the compared approaches. ‘igure 4. Comparison of different ABLH estimates expressed in terms of linear fitting for each
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