Intercomparison of Oceansat-2 and ASCAT Winds with In Situ Buoy Observations and Short-Term Numerical Forecasts

Figures & data

Fig. 1 Buoy locations.

Table 1. Statistical parameters for OSCAT and ASCAT wind speeds during the 2011 monsoon over the northern band and the tropics (ws (scat) is the monthly mean scatterometer wind speed; ws (buoy) is the monthly mean buoy wind speed; and NC is the number of collocated scatterometer winds).

Parameters	June 2011		July 2011		August 2011		September 2011
	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT
Northern Band
Mean ws (scat) (m s^−1)	6.97	5.93	7.38	7.76	7.18	7.10	8.55	8.52
Mean ws (buoy) (m s^−1)	7.80	6.49	8.07	8.12	7.95	7.79	9.13	9.42
Speed Bias (m s^−1)	−0.83	−0.55	−0.68	−0.36	−0.76	−0.69	−0.57	−0.89
Standard deviation (m s^−1)	1.62	1.61	1.73	1.51	1.86	1.76	1.97	1.98
RMSD (m s^−1)	1.93	1.72	2.00	1.25	2.13	1.70	2.02	1.87
NC	1515	727	1649	770	1564	1271	1991	978
Tropics
Mean ws (scat) (m s^−1)	8.16	7.89	7.71	7.58	7.51	7.50	7.48	7.32
Mean ws (buoy) (m s^−1)	8.17	8.15	7.90	7.84	7.67	7.80	7.67	7.46
Speed Bias (m s^−1)	−0.07	−0.25	−0.19	−0.25	−0.15	−0.29	−0.18	−0.14
Standard deviation (m s^−1)	1.49	1.19	1.57	1.29	1.59	1.22	1.60	1.19
RMSD (m s^−1)	1.54	1.11	1.70	1.17	1.70	1.07	1.74	1.00
NC	686	232	785	231	866	291	954	311

Table 2. Statistical parameters for OSCAT and ASCAT wind directions during the 2011 monsoon over the northern band and the tropics (wd (scat) is the monthly mean scatterometer wind direction; wd (buoy) is the monthly mean buoy wind direction; and NC is the number of collocated scatterometer winds).

Parameters	June 2011		July 2011		August 2011		September 2011
	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT
Northern Band
Mean wd (scat) (degrees)	185.43	184.03	208.18	232.39	202.69	203.95	188.27	214.28
Mean wd (buoy) (degrees)	188.60	197.75	217.28	232.67	206.09	205.36	192.84	217.87
wd Bias (degrees)	−3.17	−13.71	−9.29	−0.27	−3.40	−1.40	−4.57	−3.59
Standard deviation (degrees)	13.51	13.60	19.16	23.93	10.27	5.44	7.39	2.86
RMSD (degrees)	19.97	19.50	21.37	14.31	21.28	15.94	19.65	15.41
NC	1515	727	1649	770	1564	1271	1991	978
Tropics
Mean wd (scat) (degrees)	146.78	169.89	132.27	169.77	144.10	166.18	143.52	162.05
Mean wd (boy) (degrees)	149.02	168.57	132.47	172.29	143.07	166.58	144.37	161.48
wd Bias (degrees)	−2.24	1.38	−0.20	−2.52	1.03	−0.40	−0.85	0.56
Standard deviation (degrees)	4.16	5.59	4.28	4.99	4.05	5.18	3.86	2.90
RMSD (degrees)	16.86	16.48	17.96	15.58	16.86	15.51	16.90	14.90
NC	686	232	785	231	866	291	954	311

Fig. 2 Density plot for scatterometer winds with respect to buoy winds: (a) OSCAT wind speed, (b) OSCAT wind direction, (c) ASCAT wind speed, and (d) ASCAT wind direction for July 2011 over the northern band (the colour bar indicates the number of collocated scatterometer winds).

Fig. 3 As in Fig. 2, but over the tropics.

Fig. 4 Vector plot of OSCAT winds: (a) mean vector difference (the colour bar indicates the magnitude of the vector difference and (b) number of collocations (the colour bar indicates the number of collocated scatterometer winds) for July 2011.

Fig. 5 As in Fig. 4, but for ASCAT winds.

Fig. 6 Density plot for OSCAT winds with respect to model background winds over (a) the northern band (20°–90°N), (b) the tropics (20°N–20°S), and (c) the southern band (20°–90°S) for July 2011 (the colour bar indicates the number of collocated scatterometer winds).

Fig. 7 As in Fig. 6, but for ASCAT winds.

Table 3. Statistical parameters of wind speed, wind direction, zonal wind, and meridional wind for OSCAT and ASCAT with respect to NCMRWF model 6 h forecast during the 2011 monsoon over the northern latitudinal band.

Parameters	June 2011		July 2011		August 2011		September 2011
Northern Band	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT
Wind Speed
Bias (m s^−1)	0.26	0.01	0.11	−0.02	0.22	0.03	0.38	−0.22
Standard deviation (m s^−1)	2.23	1.55	2.06	1.52	2.23	1.55	2.48	1.63
Wind Direction
Bias (degrees)	0.02	−0.59	−0.44	−0.71	−0.01	−0.62	−0.09	−0.62
Standard deviation (degrees)	15.28	12.08	14.90	11.02	15.91	12.72	15.14	12.38
Zonal Wind component
Bias (m s^−1)	−0.14	−0.36	−0.26	−0.04	−0.07	−0.31	−0.03	−0.34
Standard deviation (m s^−1)	2.73	1.80	3.35	1.73	3.32	1.82	3.36	1.93
Meridional Wind component
Bias (m s^−1)	−0.12	−0.21	0.10	−0.22	0.09	−0.17	0.05	−0.14
Standard deviation (m s^−1)	2.52	1.77	3.37	1.74	3.36	1.82	3.50	1.97

Table 4. As in Table 3 but over the tropics.

Parameters	June 2011		July 2011		August 2011		September 2011
Tropics	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT
Wind Speed
Bias (m s^−1)	0.75	0.25	0.68	0.23	0.65	0.19	0.70	0.23
Standard deviation (m s^−1)	1.78	1.39	1.80	1.41	1.80	1.39	1.78	1.37
Wind Direction
Bias (degrees)	0.13	0.08	0.51	0.02	0.49	0.04	0.43	0.08
Standard deviation (degrees)	6.03	6.48	7.78	6.55	7.08	6.26	6.31	6.41
Zonal Wind component
Bias (m s^−1)	−0.13	−0.05	0.19	−0.07	−0.16	−0.02	0.05	−0.02
Standard deviation (m s^−1)	1.92	1.55	2.75	1.58	2.42	1.56	2.21	1.54
Meridional Wind component
Bias (m s^−1)	0.19	0.07	0.35	0.05	0.38	0.05	0.40	0.06
Standard deviation (m s^−1)	1.94	1.75	2.60	1.83	2.34	1.78	2.13	1.76

Table 5. As in Table 3, but over the southern latitudinal band.

Parameters	June 2011		July 2011		August 2011		September 2011
Southern Band	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT	OSCAT	ASCAT
Wind Speed
Bias (m s^−1)	−0.18	0.01	−0.18	−0.02	−0.10	0.03	−0.19	0.00
Standard deviation (m s^−1)	2.16	1.84	2.17	1.79	2.12	1.79	2.06	1.75
Wind Direction
Bias (degrees)	−0.15	−0.25	−0.80	0.55	−0.52	−0.30	−0.32	−0.49
Standard deviation (degrees)	13.19	12.12	14.69	13.13	14.06	12.91	13.53	12.73
Zonal Wind component
Bias (m s^−1)	−0.28	−0.27	−0.54	−0.32	−0.46	−0.24	−0.39	−0.25
Standard deviation (m s^−1)	2.67	2.23	3.54	2.20	3.23	2.19	2.79	2.13
Meridional Wind component
Bias (m s^−1)	0.10	0.10	0.21	0.18	0.18	0.16	0.15	0.18
Standard deviation (m s^−1)	2.65	2.36	3.78	2.29	3.53	2.33	2.91	2.29

Table 6. Statistical parameters for triple collocations of OSCAT, ASCAT, and modelled 6 h forecast winds. NC is the number of triple-collocated point.

Parameters	August 2011			September 2011
Northern Band	OSCAT vs ASCAT	OSCAT vs Model	ASCAT vs Model	OSCAT vs ASCAT	OSCAT vs Model	ASCAT vs Model
Speed Bias (m s^−1)	−1.04	−0.18	0.86	0.54	1.56	1.02
RMSVD (m s^−1)	4.85	5.42	3.85	4.66	5.13	3.38
NC	1245	1245	1245	731	731	731