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3.3 Radar dependencies
The Lemon technique implies that volume scanning radars are needed since many of the
critical features originate aloft (see Fig. 4). Both, high data quality (Joe, 2009; Lakshmanan et
al, 2007; Lakshmanan et al 2010; Lakshmanan et al, 2011) and rapid update cycles for the fast
evolving thunderstorms (Crum and Alberty, 1993; Marshall and Ballantyne, 1975). In order
to detect low level "clear air" boundaries important for the identification of convective
initiation, high sensitivity is critical. Research literature often shows many examples of
extensive clear air radar echoes that are not operationally observed. The operational
question is whether it is a radar sensitivity issue or the lack of insect targets (the clear air
targets have been identified as insects through dual-polarization signatures). Extensive clear
air echoes are commonly reported observed on the WSR-88D and primarily in certain parts
of the United States (Wilson et al, 1998). Table 5 shows the sensitivity of a small sample of
radars including the WSR-88D, WSR-98D (S Band radars) and three C Band radars, one of
which is a low powered (8 kW), travelling wave tube (TWT) solid sate pulse compression
radar (Joe, 2009; Bech et al, 2004; O'Hora and Bech, 2007). In units of dBZ, the sensitivity is a
function of range. Fifty kilometer range is arbitrarily chosen to compare the radar
sensitivities. The table shows that all these state of the art radars can have comparable
sensitivity. Therefore, the apparent lack of clear air echoes is due to the lack of local clear air
radar targets and not due to radar sensitivity or wavelength (for example, see May et al,
2004). In addition, due to the dependendence of the backscatter on the inverse frequency
squared, C Band radars should observe insects better than S Band radars.
Radar
MDS at 50 km
WSR-98D (TJ)
-6.0dBZ
WSR-98D (BJ)
-5.5 dBZ
WSR-88D (KTLX)
-7.5 dBZ
WSR-88D (KLCH)
-8.5 dBZ
WKR Conventional C Band (2 μs pulse)
-11.0 dBZ
WKR Conventional C Band (0.5 μs pulse)
-5.0 dBZ
CDV TWT (8kW) C Band (1 μs pulse)
6.0 dBZ
CDV TWT (8kW) C Band (5 μs pulse)
-7.0 dBZ
CDV TWT (8kW) C Band (NLFM 30 μs pulse)
-6.0 dBZ
CDV TWT (8kW) C Band (NLFM 40 μs pulse)
-9.0 dBZ
INM Conventional C Band (2 μs pulse)
-9.0 dBZ
Table 5. Minimum Detectable Signal of Various Radars
4. Forecast process and system design
Perhaps the most important consideration in the design of the operational radar processing,
visualization and decision-making is the underlying philosophy of the weather service,
existing systems and, of course, the capabilities and resources available (Joe et al 2002). In
many cases, the warning service requirements are driven not only by the scientific
capabilities or the needs but also by the political, societal and economic norms. Often a
warning service is an ethical and moral reaction by NHMS's to a damaging event or events
and hence it is also a political reaction by governments. This varies considerably from place
to place. These requirements are tempered by existing observational infrastructure. Are
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