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• rather enhanced in low lying coastal parts (See Fig9.5.1).
• rather deficient in areas where orographic enhancement might be expected (See Fig9.5.2). 

Fig9.5.1(left):  Precipitation accumulation T+0 to T+54 from HRES data time 00UTC 10 July 2017 for the operational 43r3 run.  Anomalous enhanced precipitation totals are focused along the coastlines of England (Cornwall and Bristol Channel) and France (Golfe de Saint-Malo) just over the adjacent sea.

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Fig9.5.2(right): Precipitation accumulation T+0 to T+48 from an equivalent run of the HRES, but with the physics changes incorporated into 45r1.  The precipitation maxima are no longer offshore and along the coast, but instead there are areas of orographically enhanced precipitation that have a much more realistic spatial structure.Rainshadow is slightly less extensive, though it is not immediately obvious whether this is better or worse.Compare with Fig 9.5.2(left).

Tropical cyclones in cycle 43r3 and earlier

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• Perturbations based on singular vectors (SV) and perturbations based on ensemble of data assimilations (EDA) have different characteristics:
  • Geographically, EDA-perturbations based perturbations on EDAs are less localized localised than SV- based perturbations based on SVs.  In particular, they have a larger amplitude over the tropics.
  • Spectrally, EDA-perturbations based perturbations on EDAs are smaller in scale.
  • Vertically, EDA-perturbations based perturbations on EDAs are more barotropic than SV-based perturbations; SV-based perturbations perturbations based on SVs.  Perturbations based on SVs show westward tilt with height typical of baroclinically unstable structures.
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  • At initial time, SV-based perturbations have a larger amplitude in potential energy than kinetic energy; perturbations based on EDA -based perturbations have a similar amplitude in potential and kinetic energy.
  • EDA perturbations grow less rapidly.
An ensemble based on EDA -based ensemble underestimates the ensemble spread.
• More reliable and accurate forecasts are obtained with a combination of EDA- and SV-based perturbations (operational since Jun 2010).

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Fig5.1.1: 1000hPa perturbed analyses and forecasts of members 1 and 2 from 12UTC 13 August 2010; the positive and negative perturbations in red and blue dashed lines respectively.  At initial time the perturbations are pair-wise anti symmetric, weakening or deepening a shallow low-pressure system on the westernmost Atlantic (upper images). 24 hours into the forecast, the perturbations in member 1 have led to the low splitting into two cyclonic pressure systems, in member 2 to a significant deepening of the single low pressure system.

Fig5.1.2:  Same as Fig5.1.1 but for 00UTC 15 August 2010. In this case the anti symmetry is still clearly seen 24 hours into the forecast, member 1 having the low deepened and displaced into a slightly more westerly position, member 2 having the low weakened and displaced into a slightly more easterly position.

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