Comparison Study of Lower-tropospheric Horizontal Wind over Sumatra, Indonesia Using NCEP/NCAR Reanalysis, Operational Radiosonde, and the Equatorial Atmosphere Radar

Abstract

Horizontal wind at 700 hPa over Sumatra (0°N, 100°E ) analyzed by National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was compared with wind observed by a VHF wind-profiling Doppler radar at Kototabang (0.20°S, 100.32°E) during 2001 2007. Radiosonde wind data at Padang (0.88°S, 100.35°E) were reported through Global Telecommunication System (GTS) for assimilation into NCEP/NCAR reanalysis. To examine if radiosonde observations at Padang improve wind quality of NCEP/NCAR reanalysis over Sumatra, dataset of radar wind, which was compared with NCEP/ NCAR reanalysis, was divided into the group when radiosonde observations were reported though GTS (Group A) and when they were not reported (Group B). For each group, correlation coefficient and regression line were computed. In Group A, both zonal and meridional winds showed better correlation coefficients (0.90 and 0.77) than in Group B (0.79 and 0.63). Amplitude of NCEP/NCAR-reanalysis zonal and meridional winds showed a better agreement in Group A (82 and 96% of radar wind) than in Group B (66 and 80% of radar wind). These results suggest that wind observations in the Indonesian Maritime Continent contribute to improve wind quality of NCEP/NCAR reanalysis there. IntroductionThe Indonesian Maritime Continent (hereafter IMC) is one of the regions where deep cumulus convection occurs most frequently (e.g., Yamanaka et al. 2008). Because cumulus activities over the Indian Ocean, IMC, and the western Pacific are modulated by synoptic-scale disturbances such as intra-seasonal variation (ISV; see Zhang 2005), many studies investigated synoptic-scale wind disturbances over them using global objective reanalyses (e.g., Matthews 2000). Previous studies have shown that assimilating observed winds to objective reanalysis contributes to improve wind quality of objective reanalysis in the tropical region. Using a windprofiling Doppler radar at Christmas Island in the central Pacific (2°N, 157°W), Gage et al. (1988) showed that monthly-mean standard deviation (bias) between observed and reanalysis winds reduced from 3 5 m s 1 (1 3 m s 1 ) to 1 2 m s 1 (less than 0.5 m s 1 ) by assimilating observed winds into objective analyses. Using radar wind data observed at 4 tropical stations, Schafer et al. (2003) showed that agreement between NCEP/NCARreanalysis and radar winds was closest at the station where radar wind data were assimilated in NCEP/ NCAR reanalysis (Christmas Island) compared with other 3 stations where radar wind data were not assimilated. The poorest agreement occurred at Piura, which is farthest from the operational radiosonde site (1234 km). Over IMC, upper-air observations assimilated into objective reanalysis are sparse. Though IMC has longitudinal extension of~4000 km, only 12 radiosonde observation sites exist over Indonesia (Yamanaka et al. 2008;Okamoto et al. 2003). Further, observations were not always carried out (later explained in Table 1). Therefore quality of wind in objective reanalysis ove...

Maritime continent coastlines controlling Earth’s climate

“…HARIMAU consisted of a radar-profiler network with meteorological Doppler radars of X-band (at Padang; e.g., Kawashima et al 2011;Mori et al 2011;Sakurai et al 2011;Kamimera et al 2012) and C-band (at Serpong near Jakarta; e.g., Wu et al 2013;Mori et al, 2018, personal communication), and wind profilers of L-band (at Pontianak, Manado, and Biak; e.g., Tabata et al 2011aTabata et al , 2011b. A large very high frequency (VHF) wind profiler called the Equatorial Atmosphere Radar (EAR) located at Kototabang (e.g., Fukao 2006;Shibagaki et al 2006;Seto et al 2009) was also included in the network. Rainfall and wind distribution data were displayed via the Internet in near real-time throughout the project.…”

“…9 The number of radiosonde stations was also increased to 22, which contributed to the improved accuracy of objective analyses at meteorological agencies worldwide (cf. Seto et al 2009). 10 In parallel with the measurements obtained by the radars and radiosondes, JAMSTEC and BPPT collaborated on buoy and shipboard observations over the Indonesian exclusive economic zone (EEZ) as part of the international network of the Tropical Ocean Climate Study (TOCS; Ando et al 2010 Yoneyama et al 2013).…”

“…9 As of March 2017, 36 C-band and 4 X-band radars are in operation, and one more radar is being installed in 2017. 10 Radiosonde observations (originally at 12 stations) reported to the global telecommunication system (GTS) were increased to more than once per day since mid-2005 (approaching twice a day during 2007); their impact on objective analysis has been shown by Seto et al (2009), and the number of stations has been increased to 22 (in addition to 2 wind-profiler and 73 pilot balloon stations) as of March 2017. 11 A "tropical night" is defined by the Japan Meteorological Agency as having the daily minimum temperature higher than 25°C, although another criterion, for example, in Germany (20°C), is somewhat lower than the Japanese definition and also lower than the usual daily minimum temperature in the IMC. 12 The typical values are observationally less than 10 2 km in the extratropics and theoretically given as the half horizontal wavelength using the gravity-wave dispersion relation, substituting the height of the sea-land breeze circulation cell as the half vertical wavelength (internal case, latitude < 30°) (e.g., Rotunno 1983;Niino 1987).…”

Evaluation of global reanalysis winds and high‐resolution regional model outputs with the 205 MHz stratosphere–troposphere wind profiler radar observations

“…Since STR uses the same technique to measure the zonal and meridional winds, we expect uniform accuracy in zonal and meridional winds in reanalysis datasets and model‐simulated winds. The outcome of the present study and earlier studies (Seto et al ., 2009; Tabata et al ., 2011) shows that zonal winds from reanalyses data are better correlated with the observed winds from WPRs than meridional winds. It indicates that the meridional wind computation in reanalyses needs improvement to get more realistic atmospheric models.…”

“…Seto et al . (2009) carried out a relative analysis of the VHF wind profiler radar (WPR) at Katlenburg (0.20°S, 100.32°E) at a single altitude (700 hPa) from Sumatra (0°N, 100°E) with the NCEP reanalysis data during 2001–2007. The study suggested improving the NCEP reanalysis wind in the Indonesian Maritime Continent region.…”