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User group experiments

Experiments modifying the temperature tendency due to radiation

Main conclusions:

1. Increasing tendency from radiation (heating at daytime, cooling at night) in the upper levels over the North Atlantic (experiment rad_2_NA_top in Table) leads to higher mean sea level pressure values over the North Atlantic and it is compensated with lower MSLP almost everywhere else (Fig. 1).
2. Nullified tendency from radiation over the North Atlantic from 900 to 100 hPa (experiment rad_0_Karl) slightly deepen the cyclone (or shift it eastwards). The output tendency from radiation remains below 1K/day after 48 hours (i.e. at 00 UTC; Fig. 2).

Explanation:

1. ?
2. The tendency due to radiation is chopped back every time step, so basically the radiation does not have too much contribution to the total tendency. However, it affects the results only slightly due to the magnitude of this sort of tendency.

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Anchor fig1 fig1 Anchor fig2 fig2 Figure 1: Difference in mean sea level pressure (in hPa) between the experiment with no temperature tendency from radiation (rad_0_NA_top) and the experiment with doubled temperature tendency from radiation (rad_2_NA_top). Figure 2: Lower panel: Cross section for 48-hour forecast of temperature tendency from radiation (in K/day, with shading) and potential temperature (in K, with isolines) along the line highlighted in red in the top panelmap. The figure graph shows the result of the experiment with zero temperature tendency from radiation (rad_0_Karl). The dotted rectangle represents the box where the tendency modification was applied.

User group experiments modifying the temperature tendency due to convection

Main conclusions:

1. Nullifying and doubling the temperature tendency due to convection in a box covering Karl in the first 48 hours (experiments con_0_Karl_48h and con_2_Karl_48h) leads to increased and decreased mean sea level pressure on the first day, respectively. The direction of the change is clear, but its magnitude is not proportional with the size of the scaling factor (confirmed also by the experiment pairs of con_0.5_def_24h and con_1.5_def_24h, con_0.5_Karl_48h and con_1.5_Karl_48h applying slightly different scaling factors). The structure of the potential vorticity also coincides with that.
2. Contrary to what we have seen in case of the radiation, the temperature tendency due to convection can reach 3 K/day between 900 and 400 hPa in the 24- and 48-hour forecasts (Fig. 3), even if we remove (con_0_Karl_48h) or halve (con_0.5_Karl_48h) the tendency in the beginning of every time step. Decreasing the convective temperature tendency results in a small extra drying.
3. Increasing the convective temperature tendency with 50 % in the first 24 hours in a small area close to the mean sea level pressure minimum of Karl (con_1.5_def_24h) leads to slight changes in the output convective tendency: small increase in the lower levels and drop over 900 hPa (Fig. 3). The scaling has straightforward effect on the precipitation especially if it is applied in a 48-hour period (con_1.5_Karl_48h; Fig. 4).

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Anchor fig3 fig3   Figure 3: Vertical profile for 48-hour forecasts of temperature tendency from different sources (in K/day) over the area highlighted in red in the top left panelright map. The top right panel graph shows the result of the control experiment, the middle and the lower panels graphs show the results of the experiments where scaling factor of 0.5 and 1.5 was applied on the convective temperature tendency (con_0.5_Karl_48h and con_1.5_Karl_48h), respectively. Please note the different scale of the x-axis.

Explanation:

1. The convection scheme continuously acts in the model, so the tendency at step +24h on 26 September 2016 is the sum of the tendencies between 00 UTC on 25 September and 00 UTC on 26 September 2016 resulted by the convection scheme during every 900 s , (i.e. 15 minutes) between 00 UTC on 25 September and 00 UTC on 26 September 2016. Therefore, even if we remove the temperature tendency due to convection at the beginning of the time step, the deep convection mechanisms considerably develop by the end of the time step.
2. More intense convection processes deepen the cyclone and the opposite happens with a reduced convection influencing also the precipitation amount.

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Anchor fig4 fig4   Figure 4: 66-hour precipitation forecasts resulted by the experiments where scaling factor of 0.5 (left; con_0.5_Karl_48h) and 1.5 (right; con_1.5_Karl_48h) was applied on the convective temperature tendency.

User group experiments modifying the temperature tendency due to cloud processes

Main conclusions:

1. Halving the temperature tendency due to cloud processes in a box following Karl in the first 48 hours (experiment cloud_0.5_Karl_48h) increases the output near-surface heating from the cloud microphysics and it is compensated by enhanced low-level cooling from the dynamics. Shallow convection seems to be less active resulting in a reduced drying near the surface. Between 800 and 400 hPa the deep convection gets more intense accompanied by more excessive heating and drying in this layer (Fig. 5). At the same time, the dynamical processes add plus moisture here.
2. Changing the temperature tendency due to cloud processes in a box covering Karl in the first 48 hours has significant impact on the precipitation over Scandinavia later (Fig. 6). Applying scaling factor of 1.5 (experiment cloud_1.5_Karl_48h) leads to an earlier precipitation maximum before 18 UTC 27 September 2016, while scaling factor of 0.5 (experiment cloud_0.5_Karl_48h) results in a delay in precipitation maximum.

Explanation:

1. ?

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