# [ncl-talk] question on dim_avg_n and dim_stddev_n

Dennis Shea shea at ucar.edu
Thu Nov 9 15:01:30 MST 2017

```Hi Andrew ...

Did you find the problem?

"Could it be there are missing values for certain storms and cycles?"  ....
quite possibly.

D

On Tue, Oct 31, 2017 at 4:18 PM, Andrew Kren - NOAA Affiliate <
andrew.kren at noaa.gov> wrote:

> Dear ncl-talk,
>
> I am computing a paired t test between control experiments sensitivity
> experiments to look at hurricane track, wind, and intensity errors. I
> compute the standard deviation of the differences and the avg of the
> differences, as well as a 95% confidence interval based on the differences.
>
> Attached is my code, see lines starting on 1127. Is this the correct way
> to compute the standard deviation and average of the differences between
> experiments? My data is a function of (storm case, forecast cycle, forecast
> hour). Reason I ask is that when I do this procedure, the average
> differences I get using this method as a function of forecast hour (which
> is what I want) is this:
>
> Variable: track_error_diff_avg (subsection)
>
> Type: float
>
> Total Size: 116 bytes
>
>             29 values
>
> Number of Dimensions: 1
>
> Dimensions and sizes: [29]
>
> Coordinates:
>
> Number Of Attributes: 1
>
>   _FillValue : 9.96921e+36
>
> (0) 3.574069
>
> (1) 5.169381
>
> (2) 4.654985
>
> (3) 1.50052
>
> (4) 3.559848
>
> (5) 3.355001
>
> (6) 4.764093
>
> (7) 8.347384
>
> (8) 7.4192
>
> (9) 8.69336
>
> (10) 12.72247
>
> (11) 17.61452
>
> (12) 17.19171
>
> (13) 11.51769
>
> (14) 9.379377
>
> (15) 11.44438
>
> (16) 7.419726
>
> (17) -3.023807
>
> (18) -18.86928
>
> (19) -3.98752
>
> (20) -4.023374
>
> (21) -14.1253
>
> (22) -7.246421
>
> (23) -10.78448
>
> (24) -23.74559
>
> (25) -40.31917
>
> (26) -51.49041
>
> (27) -34.30735
>
> (28) -9.808663
>
>
> However, when I compute the raw difference from the average track fields,
> i.e. line 1154, I get these values:
>
>
> Variable: track_error_diff_avg (subsection)
>
> Type: float
>
> Total Size: 116 bytes
>
>             29 values
>
> Number of Dimensions: 1
>
> Dimensions and sizes: [29]
>
> Coordinates:
>
> Number Of Attributes: 1
>
>   _FillValue : 9.96921e+36
>
> (0) 3.574068
>
> (1) 5.16938
>
> (2) 4.654984
>
> (3) 1.500519
>
> (4) 3.559845
>
> (5) 3.355003
>
> (6) 4.764091
>
> (7) 8.654808
>
> (8) 8.30986
>
> (9) 6.454712
>
> (10) 10.45447
>
> (11) 17.66672
>
> (12) 20.24161
>
> (13) 14.71471
>
> (14) 13.84648
>
> (15) 17.98428
>
> (16) 9.601624
>
> (17) -0.5063171
>
> (18) -14.034
>
> (19) -3.797974
>
> (20) -0.2883911
>
> (21) -11.9198
>
> (22) -9.015442
>
> (23) -6.522919
>
> (24) -61.46265
>
> (25) -74.77875
>
> (26) -40.00131
>
> (27) 52.12799
>
> (28) 76.7471
>
>
> where the values start to deviate after index 8. Is there something I am
> doing wrong? I can't seem to find out why if so. Could it be there are
> missing values for certain storms and cycles? Any help is much appreciated.
>
> --
> Andrew Kren
> Research Scientist I, Global Observing Systems Analysis (GOSA) Group
> NOAA ESRL Global Systems Division (Rm 3C515)
> 325 Broadway, Boulder, CO 80305
> (303) 497-5418
>
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