Abstract
The Ensemble Transform Kalman Filter (ETKF) is one candidate strategy for targeting observations around tropical cyclones. The characteristics of target areas identified by a revised version of the ETKF are investigated using the THORPEX Interactive Grand Global Ensemble. In order to emphasize sensitivity to the environmental flow, the axisymmetric circulation associated with the tropical cyclone is removed from each ensemble member. The guidance is found to differ markedly from the ensemble variance, and the guidance products based on ensembles from different operational centres often disagree. For the pre-recurvature stage of typhoon Sinlaku (2008), the targets correspond to asymmetries close to the typhoon, neighbouring features including the adjacent subtropical ridge and a nearby upper-level trough, and far-field features including the monsoon trough and areas of flow convergence. During and after recurvature, targets exist in the midlatitude jet upstream and downstream of the typhoon. The midlatitude targets are discernible for forecasts beyond 3 days. The sensitivity to hypothetical observations of wind is more pronounced than those of temperature or specific humidity. The targets based on upper-level observations correspond to the outflow of the tropical cyclone and nearby and remote jets, while the lower-level targets correspond to confluent flow near the cyclone. Multiple remote targets are evident, particularly for longer forecast times, and some of these may be spurious. When ensemble forecasts initialized at different times are used for the same case, the characteristics of the guidance differ, although not dramatically. Future priorities include the evaluation of the effects of assimilating observations sampled in target areas versus those in non-target areas, and the improvement of the data assimilation methodology assumed in the ETKF.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 503-520 |
| Number of pages | 18 |
| Journal | Quarterly Journal of the Royal Meteorological Society |
| Volume | 137 |
| Issue number | 655 |
| DOIs | |
| State | Published - Jan 2011 |
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Keywords
- Data assimilation
- Targeted observations
- Typhoon Sinlaku
ASJC Scopus subject areas
- Atmospheric Science
Cite this
Characteristics of Ensemble Transform Kalman Filter adaptive sampling guidance for tropical cyclones. / Majumdar, Sharanya J; Chen, Shin Gan; Wu, Chun Chieh.
In: Quarterly Journal of the Royal Meteorological Society, Vol. 137, No. 655, 01.2011, p. 503-520.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Characteristics of Ensemble Transform Kalman Filter adaptive sampling guidance for tropical cyclones
AU - Majumdar, Sharanya J
AU - Chen, Shin Gan
AU - Wu, Chun Chieh
PY - 2011/1
Y1 - 2011/1
N2 - The Ensemble Transform Kalman Filter (ETKF) is one candidate strategy for targeting observations around tropical cyclones. The characteristics of target areas identified by a revised version of the ETKF are investigated using the THORPEX Interactive Grand Global Ensemble. In order to emphasize sensitivity to the environmental flow, the axisymmetric circulation associated with the tropical cyclone is removed from each ensemble member. The guidance is found to differ markedly from the ensemble variance, and the guidance products based on ensembles from different operational centres often disagree. For the pre-recurvature stage of typhoon Sinlaku (2008), the targets correspond to asymmetries close to the typhoon, neighbouring features including the adjacent subtropical ridge and a nearby upper-level trough, and far-field features including the monsoon trough and areas of flow convergence. During and after recurvature, targets exist in the midlatitude jet upstream and downstream of the typhoon. The midlatitude targets are discernible for forecasts beyond 3 days. The sensitivity to hypothetical observations of wind is more pronounced than those of temperature or specific humidity. The targets based on upper-level observations correspond to the outflow of the tropical cyclone and nearby and remote jets, while the lower-level targets correspond to confluent flow near the cyclone. Multiple remote targets are evident, particularly for longer forecast times, and some of these may be spurious. When ensemble forecasts initialized at different times are used for the same case, the characteristics of the guidance differ, although not dramatically. Future priorities include the evaluation of the effects of assimilating observations sampled in target areas versus those in non-target areas, and the improvement of the data assimilation methodology assumed in the ETKF.
AB - The Ensemble Transform Kalman Filter (ETKF) is one candidate strategy for targeting observations around tropical cyclones. The characteristics of target areas identified by a revised version of the ETKF are investigated using the THORPEX Interactive Grand Global Ensemble. In order to emphasize sensitivity to the environmental flow, the axisymmetric circulation associated with the tropical cyclone is removed from each ensemble member. The guidance is found to differ markedly from the ensemble variance, and the guidance products based on ensembles from different operational centres often disagree. For the pre-recurvature stage of typhoon Sinlaku (2008), the targets correspond to asymmetries close to the typhoon, neighbouring features including the adjacent subtropical ridge and a nearby upper-level trough, and far-field features including the monsoon trough and areas of flow convergence. During and after recurvature, targets exist in the midlatitude jet upstream and downstream of the typhoon. The midlatitude targets are discernible for forecasts beyond 3 days. The sensitivity to hypothetical observations of wind is more pronounced than those of temperature or specific humidity. The targets based on upper-level observations correspond to the outflow of the tropical cyclone and nearby and remote jets, while the lower-level targets correspond to confluent flow near the cyclone. Multiple remote targets are evident, particularly for longer forecast times, and some of these may be spurious. When ensemble forecasts initialized at different times are used for the same case, the characteristics of the guidance differ, although not dramatically. Future priorities include the evaluation of the effects of assimilating observations sampled in target areas versus those in non-target areas, and the improvement of the data assimilation methodology assumed in the ETKF.
KW - Data assimilation
KW - Targeted observations
KW - Typhoon Sinlaku
UR - http://www.scopus.com/inward/record.url?scp=79952524608&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79952524608&partnerID=8YFLogxK
U2 - 10.1002/qj.746
DO - 10.1002/qj.746
M3 - Article
AN - SCOPUS:79952524608
VL - 137
SP - 503
EP - 520
JO - Quarterly Journal of the Royal Meteorological Society
JF - Quarterly Journal of the Royal Meteorological Society
SN - 0035-9009
IS - 655
ER -