the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Observations of anomalous propagation over waters near Sweden
- Radar Electronic Warfare Systems, Department for C4ISR, Swedish Defence Research Agency, Linköping, Sweden
- Radar Electronic Warfare Systems, Department for C4ISR, Swedish Defence Research Agency, Linköping, Sweden
Abstract. Radio waves propagating in the atmosphere are affected by the prevailing atmospheric state. The state of the atmosphere can cause radio waves to refract more or less towards the ground. When the refractive index of the atmosphere differs from standard atmospheric conditions the propagation is called anomalous. Radars which are affected by anomalous propagation can receive ground clutter far beyond the radar horizon. In this work 4.5 years of data from five operational Swedish C-band dual polarization weather radars are presented. Analyses of the data reveal a strong seasonal cycle and weaker diurnal cycle in ground clutter from coastal regions across nearby waters. The impact of anomalous propagation on ground clutter, measured with horizontal and vertical polarization, was compared but no clear difference was found.
Lars Norin
Status: open (until 23 Feb 2023)
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RC1: 'Comment on amt-2022-299', Anonymous Referee #1, 13 Jan 2023
reply
Review of manuscript ‘Observations of anomalous propagation over waters near Sweden’ submitted to ATM
General Comments
This manuscript addresses a relevant topic, an analysis of anomalous propagation echoes upon weather radar observations, clearly well suited to Atmospheric Measurement Techniques. The amount of data used (several years, several radars, and also single and dual polarization observations) is a strong aspect of the study. The methodology proposed, essentially subtracting the Doppler filtered reflectivity from the total reflectivity, despite it is not new it is an adequate choice and provides interesting results for the community of radar operators and users of radar data. Overall the text is clear and well structured so I think it is a valuable contribution and should be considered for publication. I list bellow a list requests to clarify some aspects and some suggestions for possible improvement.
Specific Comments
- P2 line 34, suggest: on radar systems -> on radar systems observations [or similar]
- P2 line 48. Here (or later in the paragraph) the text could cite Bech et al (2007) – see reference below – as they show observations and NWP simulations of a case study of intense superrefraction from the Hemse radar, similarly as in this manuscript.
- P3 line 65. Did the author check if the -32 dBZ signal value can be observed at all ranges considered (up to 240 km), i.e. are the radars sensitive enough for that? In case this is not the case please comment possible effects on the results. Please clarify in the text.
- P4 line 69. Please clarify if the analysis is performed on polar volume data (radar pixels of 250 m x 1 degree) or in cartesian data.
- P5 line 109. Please specify if the radar horizon shown in Fig. 2d is calculated considering the lower part of the 3 dB beamwidth or otherwise (for example the center of the beam). In any case, side lobes could still contribute to clutter, a possibility the text could mention.
- P7 line 134. Can you please clarify here which time resolution are you using for the values stored as a function of time of day? It is not clear to this reviewer if it is the original 5 min resolution.
- P13 line 225. Suggest: environment -> atmospheric conditions [I think the term ‘environment’ is too general and the focus is really on the atmospheric conditions]
- P14 line 231. Readers not familiar with the geographical region of study may not know where the Gulf of Bothnia is – this and other locations in the text such as Gotland could be indicated for example in Figure 1.
- P14 line 238. The effect of subrefraction shouldn’t be a decrease of detected ground clutter echo compared to normal propagation conditions, at least close to the radars?
- P15 lines 250 – 255. The text could also comment on the possible relation of the diurnal and seasonal cycle of ground clutter with that of precipitation, in particular warm season convective precipitation.
Technical Comments
- P1, Abstract, suggest: can receive ground clutter -> can observe ground clutter [similarly in P2 line 42]
- P1 line 10, Suggest: can also -> are also
- P2 line 53. Please check citation style: should it be Essen et al., 2004, 2012 similarly as Danklmayer., … in the same line?
- P3 Table 2. Suggest: Gain -> Antenna gain
- P3 line 71 and 72. I suggest converting the footnote information into references, quoted in the text and listed in the references section.
- P6 Fig 2 caption. Island Gotland or Gotland island? Please check.
- P7 line 132. Suggest: values = - 32 dBZ -> value = - 32 dBZ
- P11 line 206 typo : In can be -> It can be
Reference
Bech, J., Gjertsen, U., & Haase, G. (2007). Modelling weather radar beam propagation and topographical blockage at northern high latitudes. Quarterly Journal of the Royal Meteorological Society 133(626), 1191-1204.
Lars Norin
Lars Norin
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