Ensemble-based observation impact estimates using the NCEP GFS

Figures & data

Table 1 Observation types assimilated in the experiment

Type of data	Description	800 hPa~	400–800 hPa	125–400 hPa	~125 hPa	Total (1000 s)
Aircraft	u, v, and T observations from the aircrafts	37.2	53.9	81.7	0.0	172.7
Radiosonde	Radiosonde observations (u, v, T, q and Ps)	9.5	13.2	13.8	18.4	54.8
Satellite_Wind	Atmospheric motion vectors (u and v) from geostationary satellites	31.2	1.8	62.8	0.1	95.8
GPSRO	GPS radio occultation	1.4	9.4	17.8	67.0	95.5
Land-surface	Ps observations from land-surface stations	53.4	1.0	0.0	0.0	54.4
Marine-surface	Surface u, v, T, q and Ps observations from the buoys and ships	23.1	0.0	0.0	0.0	23.1
MODIS_Wind	Atmospheric motion vectors (u and v) from MODIS	0.8	26.1	9.2	0.0	36.1
ASCAT_Wind	u and v observations from ASCAT scatterometer over ocean	16.7	0.0	0.0	0.0	16.7
PIBAL	u and v observations from pilot balloons	0.8	0.6	0.4	0.2	1.9
NEXRAD_Wind	u and v observations from the NEXRAD (radar)	6.5	6.6	0.4	0.0	13.5
Profiler_Wind	u and v observations from the wind profilers	1.2	5.1	4.9	0.6	11.8
Dropsonde	Flight-level reconnaissance and dropsonde (u, v, T and q)	0.1	0.1	0.1	0.0	0.2
WINDSAT_Wind	u and v observations from ASCAT scatterometer over ocean (super observation)	0.8	0.0	0.0	0.0	0.8
TCVital	Pseudo surface pressure observations at tropical cyclone storm centre	0.0006	0.0	0.0	0.0	0.0006
Ozone	Ozone retrievals from satellite radiances	0.9	1.8	1.8	9.9	14.4
AMSUA	Satellite microwave sounder radiances (from five satellites)	144.2	48.6	123.8	269.2	585.8
IASI	Satellite infrared hyperspectral sounder radiances	140.5	116.6	258.5	627.4	1143.0
Aqua_AIRS	Satellite infrared hyperspectral sounder radiances	59.8	90.0	195.1	285.4	630.2
ATMS	Satellite microwave sounder radiances (from Suomi-NPP)	41.4	26.1	29.3	52.8	149.6
HIRS	Satellite infrared radiances (from two satellites)	13.0	18.0	40.8	47.1	118.9
MHS	Satellite microwave sounder radiances (from three satellites)	31.7	29.3	5.8	0.0	66.8
GOES	GOES infrared sounder radiances (GOES13 and 15)	10.3	8.6	13.9	7.0	39.8
SEVIRI	SEVIRI clear sky radiances	0.2	2.7	3.2	0.0	6.1

The third to sixth columns show the average number of observations assimilated on each vertical layer in one analysis (in thousands). Peak pressure of weighting function is used as vertical position of satellite radiance observation. u, v, T, q and Ps represents u and v wind components, temperature, specific humidity and surface pressure, respectively.

Fig. 1 Time series of the total forecast error reduction of each estimate (unit: J kg⁻¹). Black, red and blue lines show the actual forecast error reduction verified against the own analysis, estimated error reduction from the EnKF-based method with fixed localisation (fixed) and with moving localisation (advected). Numbers on upper left corner show the correlation and RMSE of each estimate to the actual forecast error reduction.

Fig. 2 Estimated average 24-hour forecast error reduction contributed from each observation types (moist total energy, J kg⁻¹). (a) represents the total error reduction and (b) represents error reduction per observation.

Fig. 3 Same as Fig. 2 but with the dry total energy norm (J kg⁻¹)

Fig. 4 Estimated AIRS satellite radiance observation impacts classified by channel with the moist total energy (red for channels sensitive below 300 hPa and magenta above 300 hPa, J kg⁻¹), and only the moist term of the total energy (blue for channels sensitive below 300 hPa and aqua above 300 hPa, J kg⁻¹). Average estimated forecast error reduction from a single observation is shown. Vertical bars represent the 95% confidence interval of the average values.

Fig. 5 Estimated average observation impacts of a) radiosonde and b) aircraft classified by observed level (moist total energy, J kg⁻¹). Average estimated forecast error reduction by a single observation is shown.

Fig. 6 Average number of assimilated radiosonde observations (a) from 250 to 125 hPa, (b) from 800 to 600 hPa and aircraft observations (c) from 250 to 125 hPa and (d) from 800 to 600 hPa in each 5°×5° area for one analysis.

Fig. 7 Average impact (moist total energy, J kg⁻¹) of a single radiosonde profile from the fixed land stations. Only the stations that have more than 20 profiles in the period are shown. Numbers 4220 (Egedesminde) and 4270 (Narssassuaq) indicate the location of the stations shown in Fig. 8.

Fig. 8 Comparison of the radiosonde observations from Narssassuaq (red line, 4270) and Egedesminde (blue line, 4220) showing (a) average impacts (J kg⁻¹) of each observation element (solid: temperature, dashed: winds, dotted: humidity) on each pressure level by one profile and observation departure statistics (dashed: bias, solid: standard deviation) of (b) temperature (K) and (c) wind speed (m s⁻¹).

Table 2 Width of longitude used for the local area on each latitude band

Latitude	Width for longitude (°)
60N–90N	60
50N–80N	40
40N–70N	30
30N–60N	20
20N–50N	20
10N–40N	15
0N–30N	15
10S–20N	15

Only the values for Northern hemisphere are shown since it is symmetric in the Southern Hemisphere.

Table 3 List of local 24-hour forecast failure cases (initial time from 00 UTC, 8 January 2012, to 18 UTC 7 February 2012)

Initial	Area	Size	Rate	N	Denied observation (denied number/total number)	Change (estimate)
06 UTC JAN 12	50N–80N 145E–175W	1.99	1.36	5	AMSUA ch4, 5, 6 (2735/125 063)	−8.7% (−19.5%)
00 UTC JAN 16	30N–60N 20W–0	2.71	1.35	6	GPSRO 600–950 hPa (50/4918)	−0.6% (−4.3%)
18 UTC JAN 27	30S–0 105E–120E	2.40	1.21	1	AIRS (19 908/670 041)	−0.2% (−6.0%)
00 UTC JAN 30	70S–40S 165E–165W	2.00	1.25	6	AMSUA ch1, 3, 4, 5, 15 (3822/164 934)	−4.7% (−12.8%)
06 UTC FEB 2	50N–80N 150W–110W	3.01	1.22	5	GPSRO 250–400 hPa, 600–850 hPa (407/13 092)	−11.7% (−8.7%)
06 UTC FEB 4	30N–60N 150W–130W	1.81	1.26	3	IASI (57 950/1 177 256), HIRS ch3, 4, 9, 11, 12, 14, 15 (785/73 419), Aircraft 950 hPa~, 125–600 hPa (5794/100 896)	−25.5% (−81.6%)
18 UTC FEB 6	60N–90N 40E–100E	1.71	1.38	2	MODIS_Wind (10 970/43 452)	−28.4% (−47.7%)

The third, fourth and fifth columns show the forecast error size normalized with the time-averaged error, the rate of the error size compared with the error of 30-hour forecast from the previous analysis, and the number of areas that meet the criteria. Sixth column shows the denied observation type based on the observation impact estimates, number of denied observations and total number of observations with this observation type assimilated in the original analysis. Finally, seventh column shows the change of the 24-hour local forecast error for observation denial experiment and corresponding estimated forecast error change in the parenthesis. The case shown in bold font is the example shown in Fig. 9.

Fig. 9 Twenty-four hour forecast error of 500 hPa geopotential height (unit: m, 18 UTC 6 February 2012 initial) from original analysis (left) and forecast change due to the removal of the MODIS polar wind observations in the data-denial experiment (middle: actual change and right: projection on the ensemble perturbations). Black contours show the analysis. Magenta cones show the target area of the observation impact estimate.