document - Cosmo

More documents

Recommendations

Info

1 Working Group on Data Assimilation 36 (not shown), remains slightly positive for the 12-UTC runs, and becomes even moderately negative for the 0-UTC runs. Whether this result given by the ETS reflects a real degradation or is an effect of the double penalty problem inherent to the ETS still needs to be evaluated. The upper-air verification against radiosonde data (Figure 4) indicates that LHN modifies the vertical stratification in the troposphere significantly. In the analyses, it cools and, in terms of absolute humidity, dries the lower troposphere (below 750 hPa resp. 850 hPa) and heats and moistens the upper troposphere (above 600 hPa). As a result, the stability is increased considerably between 750 hPa and 600 hPa . This may be due to an enhanced triggering of convection (reflected by the higher precipitation rates), which acts to reduce atmospheric instability. In terms of rms error, the fit of the analyses to the assimilated temperature and humidity radiosonde observations is decreased. However, the overall impact on the forecasts is very close to neutral (for temperature, humidity, and wind). 4 Concluding Remarks Several adaptions to the LHN algorithm have been developed to mitigate the problems of LHN related to the prognostic treatment of precipitation. Most importantly, a vertically averaged precipitation flux is used as a ’reference precipitation’ instead of the real model precipitation for comparison to the observed precipitation. The revised LHN scheme has been tested for an 11-day convective summer period. During the assimilation, the simulated rain patterns agree well with radar observations, and the overestimation of precipitation is reduced significantly compared to previous LHN versions. In the forecasts, the impact on precipitation decreases rapidly, similarly to past experiments using a diagnostic treatment of precipitation. With respect to other forecast parameters, the overall impact is nearly neutral, e.g. in terms of rmse against radiosonde observations. Thus, the problems related to prognostic precipitation appear to be mitigated to a satisfactory degree. However, the scheme needs still to be tested for stratiform precipitation, and at least two important shortcomings remain. Firstly, this is the rapid decrease of benefit in the forecasts, and secondly, there are indications that the LHN forcing is too strong: • The surface pressure fields indicate that strong gravity waves are induced during the assimilation. While local pressure disturbances of 2 − 3 hPa can be realistic for convective systems, they sometimes exceed 5 hPa in LHN simulations. The fact that these perturbations do also occur before precipitation is triggered by LHN indicates that they are not primarily linked to the problems related to prognostic precipitation. • In comparison to surface observations, the convective outflow appears to be too strong (Leuenberger, personal communication). • LHN tends to stabilise the mid troposphere too much. • LHN leads to significant cooling and drying of the planetary boundary layer (PBL). This is likely to contribute to the rapid decrease of impact in the precipitation forecasts. Hence, there is still a need to improve and better balance the scheme. One line of thought is to modify the vertical distribution of LHN increments and add (or take away) more energy and humidity at lower levels and less further above. Unless this is found to require larger LHN increments altogether, it may reduce the effects on the stratification and possibly even extend slightly the period of positive impact on predicted precipitation as a result of increased PBL humidity and decreased stability. To pave the way for developing modifications or new methods with significantly longer forecast impact, a better understanding is needed COSMO Newsletter No. 6
1 Working Group on Data Assimilation 37 of how the model itself produces convection, which conditions (such as low-level moisture convergence) it needs, and consequently what kind of observational information and forcing it should be given at which scale. References Baldauf, M., J.-P. Schulz, 2004: Prognostic precipitation in the Lokal Modell (LM) of DWD. COSMO Newsletter, No. 4, 177 - 180. Gassmann, A., 2002: 3D-transport of precipitation. COSMO Newsletter, No. 2, 113 - 117. Klink, S., K. Stephan, 2005: Latent heat nudging and prognostic precipitation. COSMO Newsletter, No. 5, 124 - 131. COSMO Newsletter No. 6
Page 1: Consortium July 2006 for Small−Sc
Page 4 and 5: Contents ii 4 Working Group on Inte
Page 6 and 7: Contents iv COSMO Newsletter No. 6
Page 8 and 9: Editorial 2 We would like to thank
Page 10 and 11: 1 Working Group on Data Assimilatio
Page 50 and 51: 2 Working Group on Numerical Aspect
Page 88 and 89: 3 Working Group on Physical Aspects
Page 90 and 91: 3 Working Group on Physical Aspects
Page 92 and 93:
3 Working Group on Physical Aspects
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
4 Working Group on Interpretation a
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
5 Working Group on Verification and
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205:
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
6 Working Group on Implementation a
Page 218 and 219:
6 Working Group on Implementation a
Page 220 and 221:
7 External Contributions 214 Figure
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
7 External Contributions 220 An Obj
Page 228 and 229:
7 External Contributions 222 a b c
Page 230 and 231:
7 External Contributions 224 • Py
Page 232 and 233:
7 External Contributions 226 lbdcli
Page 234 and 235:
7 External Contributions 228 MSLP [
Page 236 and 237:
7 External Contributions 230 22 20
Page 238 and 239:
7 External Contributions 232 0 -5 -
Page 240 and 241:
7 External Contributions 234 encour
Page 242 and 243:
7 External Contributions 236 The Ef
Page 244 and 245:
7 External Contributions 238 Veloci
Page 246 and 247:
7 External Contributions 240 WARMRA
Page 248 and 249:
7 External Contributions 242 1 Intr
Page 250 and 251:
Page 252 and 253:
7 External Contributions 246 Numeri
Page 254 and 255:
7 External Contributions 248 Erzgeb
Page 256 and 257:
7 External Contributions 250 Simula
Page 258 and 259:
7 External Contributions 252 1.2 1
Page 260 and 261:
7 External Contributions 254 a) b)
Page 262 and 263:
7 External Contributions 256 Hartje
show all

document - Cosmo

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?