A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model

Ulrik Smith Korsholm, Claus Petersen, Bent Hansen Sass, Niels Woetmann Nielsen, David Getreuer Jensen, Bjarke Tobias Olsen, Rasphal Gill, Henrik Vedel

Research output: Contribution to journalJournal articleResearchpeer-review

14 Citations (Scopus)

Abstract

A new approach for assimilation of 2D precipitation in numerical weather prediction models is presented and tested in a case with convective, heavy precipitation. In the scheme a nudging term is added to the horizontal velocity divergence tendency equation. In case of underproduction of precipitation, the strength of the nudging is proportional to the offset between observed and modelled precipitation, leading to increased moisture convergence. If the model over-predicts precipitation, the low level moisture source is reduced, and in-cloud moisture is nudged towards environmental values. The method was implemented in the Danish Meteorological Institute numerical weather prediction (DMI NWP) nowcasting system, running with hourly cycles, performing a surface analysis and 3D variational analysis for upper air assimilation at each cycle restart, followed by nudging assimilation of precipitation and then a free forecast. The precipitation fields are based on a 2D composite CAPPI (constant altitude plan position indicator) field made from observations with the DMI weather radars, and have a 10 min time resolution. The results obtained in this study indicate that the new method implies fast adjustment of the dynamical state of the model to facilitate precipitation release when the model precipitation intensity is too low. Removal of precipitation is shown to be of importance and the position of the model precipitation cells becomes skilful even at the smallest scales (∼3 km). Bias is reduced for low and extreme precipitation rates. In this meteorological case, the usage of the nudging procedure has been shown to improve the prediction of heavy precipitation substantially.
Original languageEnglish
JournalMeteorological Applications
Volume22
Issue number1
Pages (from-to)48-59
Number of pages12
ISSN1350-4827
DOIs
Publication statusPublished - 2015

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radar
moisture
weather
prediction
nowcasting
environmental values
precipitation intensity
divergence
assimilation
air
method
analysis

Keywords

  • NWP nowcasting
  • Rapid update cycle
  • Nudging
  • Divergence
  • Radar-derived precipitation

Cite this

Korsholm, U. S., Petersen, C., Sass, B. H., Nielsen, N. W., Jensen, D. G., Olsen, B. T., ... Vedel, H. (2015). A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model. Meteorological Applications, 22(1), 48-59. https://doi.org/10.1002/met.1466
Korsholm, Ulrik Smith ; Petersen, Claus ; Sass, Bent Hansen ; Nielsen, Niels Woetmann ; Jensen, David Getreuer ; Olsen, Bjarke Tobias ; Gill, Rasphal ; Vedel, Henrik. / A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model. In: Meteorological Applications. 2015 ; Vol. 22, No. 1. pp. 48-59.
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abstract = "A new approach for assimilation of 2D precipitation in numerical weather prediction models is presented and tested in a case with convective, heavy precipitation. In the scheme a nudging term is added to the horizontal velocity divergence tendency equation. In case of underproduction of precipitation, the strength of the nudging is proportional to the offset between observed and modelled precipitation, leading to increased moisture convergence. If the model over-predicts precipitation, the low level moisture source is reduced, and in-cloud moisture is nudged towards environmental values. The method was implemented in the Danish Meteorological Institute numerical weather prediction (DMI NWP) nowcasting system, running with hourly cycles, performing a surface analysis and 3D variational analysis for upper air assimilation at each cycle restart, followed by nudging assimilation of precipitation and then a free forecast. The precipitation fields are based on a 2D composite CAPPI (constant altitude plan position indicator) field made from observations with the DMI weather radars, and have a 10 min time resolution. The results obtained in this study indicate that the new method implies fast adjustment of the dynamical state of the model to facilitate precipitation release when the model precipitation intensity is too low. Removal of precipitation is shown to be of importance and the position of the model precipitation cells becomes skilful even at the smallest scales (∼3 km). Bias is reduced for low and extreme precipitation rates. In this meteorological case, the usage of the nudging procedure has been shown to improve the prediction of heavy precipitation substantially.",
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author = "Korsholm, {Ulrik Smith} and Claus Petersen and Sass, {Bent Hansen} and Nielsen, {Niels Woetmann} and Jensen, {David Getreuer} and Olsen, {Bjarke Tobias} and Rasphal Gill and Henrik Vedel",
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Korsholm, US, Petersen, C, Sass, BH, Nielsen, NW, Jensen, DG, Olsen, BT, Gill, R & Vedel, H 2015, 'A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model' Meteorological Applications, vol. 22, no. 1, pp. 48-59. https://doi.org/10.1002/met.1466

A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model. / Korsholm, Ulrik Smith; Petersen, Claus; Sass, Bent Hansen; Nielsen, Niels Woetmann; Jensen, David Getreuer; Olsen, Bjarke Tobias; Gill, Rasphal; Vedel, Henrik.

In: Meteorological Applications, Vol. 22, No. 1, 2015, p. 48-59.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model

AU - Korsholm, Ulrik Smith

AU - Petersen, Claus

AU - Sass, Bent Hansen

AU - Nielsen, Niels Woetmann

AU - Jensen, David Getreuer

AU - Olsen, Bjarke Tobias

AU - Gill, Rasphal

AU - Vedel, Henrik

PY - 2015

Y1 - 2015

N2 - A new approach for assimilation of 2D precipitation in numerical weather prediction models is presented and tested in a case with convective, heavy precipitation. In the scheme a nudging term is added to the horizontal velocity divergence tendency equation. In case of underproduction of precipitation, the strength of the nudging is proportional to the offset between observed and modelled precipitation, leading to increased moisture convergence. If the model over-predicts precipitation, the low level moisture source is reduced, and in-cloud moisture is nudged towards environmental values. The method was implemented in the Danish Meteorological Institute numerical weather prediction (DMI NWP) nowcasting system, running with hourly cycles, performing a surface analysis and 3D variational analysis for upper air assimilation at each cycle restart, followed by nudging assimilation of precipitation and then a free forecast. The precipitation fields are based on a 2D composite CAPPI (constant altitude plan position indicator) field made from observations with the DMI weather radars, and have a 10 min time resolution. The results obtained in this study indicate that the new method implies fast adjustment of the dynamical state of the model to facilitate precipitation release when the model precipitation intensity is too low. Removal of precipitation is shown to be of importance and the position of the model precipitation cells becomes skilful even at the smallest scales (∼3 km). Bias is reduced for low and extreme precipitation rates. In this meteorological case, the usage of the nudging procedure has been shown to improve the prediction of heavy precipitation substantially.

AB - A new approach for assimilation of 2D precipitation in numerical weather prediction models is presented and tested in a case with convective, heavy precipitation. In the scheme a nudging term is added to the horizontal velocity divergence tendency equation. In case of underproduction of precipitation, the strength of the nudging is proportional to the offset between observed and modelled precipitation, leading to increased moisture convergence. If the model over-predicts precipitation, the low level moisture source is reduced, and in-cloud moisture is nudged towards environmental values. The method was implemented in the Danish Meteorological Institute numerical weather prediction (DMI NWP) nowcasting system, running with hourly cycles, performing a surface analysis and 3D variational analysis for upper air assimilation at each cycle restart, followed by nudging assimilation of precipitation and then a free forecast. The precipitation fields are based on a 2D composite CAPPI (constant altitude plan position indicator) field made from observations with the DMI weather radars, and have a 10 min time resolution. The results obtained in this study indicate that the new method implies fast adjustment of the dynamical state of the model to facilitate precipitation release when the model precipitation intensity is too low. Removal of precipitation is shown to be of importance and the position of the model precipitation cells becomes skilful even at the smallest scales (∼3 km). Bias is reduced for low and extreme precipitation rates. In this meteorological case, the usage of the nudging procedure has been shown to improve the prediction of heavy precipitation substantially.

KW - NWP nowcasting

KW - Rapid update cycle

KW - Nudging

KW - Divergence

KW - Radar-derived precipitation

KW - NWP nowcasting

KW - Rapid update cycle

KW - Nudging

KW - Divergence

KW - Radar-derived precipitation

U2 - 10.1002/met.1466

DO - 10.1002/met.1466

M3 - Journal article

VL - 22

SP - 48

EP - 59

JO - Meteorological Applications

JF - Meteorological Applications

SN - 1350-4827

IS - 1

ER -