Verification and Case Studies for Urban Effectsin HIRLAM Numerical Weather Forecasting

A. Baklanov, A. Mahura, C. Petersen, N.W. Nielsen, B. Amstrup

Danish Meteorological Institute, DMI, Copenhagen, Denmark

3-4 May 2007, COST-728 Workshop on “Model Urbanization Strategy” UKMO, Exeter, United Kingdom

Goal and Specific Objectives

GOAL: Evaluate effects of urbanization of numerical weather prediction (NWP)

model on simulating meteorological fields for specific cases and overall model performance over the urbanized areas

SPECIFIC OBJECTIVES: Perform short- and long-term simulations of meteorological fields using

DMI-HIRLAM-U01/I01 models in two modes: control vs. urbanized runs

Evaluate effects of urbanization on temporal-spatial structure and variability of meteorological fields

Estimate on a diurnal cycle the differences between control and urbanized runs for meteorological variables such as surface pressure, temperature, wind, and relative humidity

HIRLAMDomains, Land-Use Classification, & Urban Features

Domain - DMI-HIRLAM-U01 (1.4 km) Focus - Island of Zeeland (I01) Land surface scheme - Interaction Soil-Biosphere-Atmosphere

(ISBA) Tiles - 5 (low vegetation, forest, ice, water, bare soil) + urban

(fraction >0.1+)

HIRLAM Numerical Weather Prediction Modelling

Model DMI-HIgh Resolution Limited Area Model (HIRLAM)

Boundary conditions DMI-HIRLAM-T15 -> -S05 -> U01/I01

Runs control vs urbanized (i.e. modif ISBA scheme) for U01/I01 domain

Modification/ Urbanization SIMPLE: roughness and anthropogenic heat flux for urban grid cells BEP: Building effect parameterization module

Output 3D meteorological fields (40 levels) for 2 types of runs

Module 1 (DMI etc): Analytical urban parameterisations (SIMPLE)

(i) Displacement height,(ii) Effective roughness and flux

aggregation, (iii) Effects of stratification on the

roughness (Zilitinkevich et al, 2004),

(iv) Different roughness for momentum, heat, and moisture;

(v) Calculation of anthropogenic and storage urban heat fluxes;

(vi) Prognostic MH parameterisations for SBL;

(vii) Parameterisations of wind profile in canopy layer (Coceal and Belcher, 2004; Zilitinkevich and Baklanov, 2004).

1st NWP layer

HIRLAMApproaches + Evaluation of Modelling Results

1. Long-term simulations

2. Short-term simulations - specific meteorological situations

3. NWP Control vs. urbanized runs

1. Diurnal cycle

2. Difference fields for control vs. urbanized runs

3. Temperature at 2m, wind at 10m, rel humidity, surf. pressure

4. Focus: impact of urbanized areas on meteorological fields

Typical Wind Conditions : SIMPLE URBAN

06 UTC

------------------ Difference (control vs. urbanized run) field for wind at 10 m ------------------

------------------ Difference (control vs. urbanized run) field for temperature at 2 m ------------------

12 UTC 18 UTC

Low Wind Conditions : SIMPLE URBAN

03 UTC

------------------ Difference (control vs. urbanized run) field for wind at 10 m ------------------

------------------ Difference (control vs. urbanized run) field for temperature at 2 m ------------------

12 UTC 21 UTC

Low Wind Conditions : BEP URBAN

Difference plots between outputs of DMI-HIRLAM vs. DMI-HIRLAM+BEP

for (a) wind velocity at 10 m and

(b) air temperature at 2 m for

20 UTC forecast on 12 April 2005

(a)

(b)

HIRLAM NWP Model Performance: Overall

all stations

HIRLAM NWP Model Performance: Over Urban Areas

Wind velocity at 10 m (w10s, in m/s; top panel) &Air temperature at 2 m (T2m, in deg. C; lower panel) based on the DMI-HIRLAM-U01 control (NOA) vs urbanized runs (A20, ZO2) vs. observational data (obs)

Værløse urban station (55.8ºN, 12.3ºE)

located in metropolitan Copenhagen

Conclusions

Long-term runs with the DMI-HIRLAM-U01/I01 high resolution urbanized model showed a slight improvement for the overall NWP model performance, &

this improvement is more considerable over the urbanized areas

Differences between NWP control vs. urbanized runs: For typical wind conditions:

wind at 10 m (m/s) <0.5 (max up to 1.5, at midday) temperature at 2 m (ºC) <0.25 (max up to 0.5, at nighttime) relative humidity (%) > 3 (max up to 5, at midday)

For low wind conditions: wind at 10 m (m/s) >1 (max up to 3 at nighttime) temperature at 2 m (ºC) >0.5 (max up to 1.5, at nighttime) relative humidity > 4 (max up to 7, at midday)

Plans

Long-term simulations by DMI-HIRLAM high resolution model urbanized version (on-going runs): HIRLAM+BEP - building effect parameterization module, HIRLAM+SM2_U - soil model for sub-meso scales urbanized version,

At first, at least, for 1-2 months; Second, for a longer period (year) in order to evaluate month-to-month

variability.

Thank you

Computing DMI facilities of NEC SX6 Advice of DMI EDB Computer Support

Department

Financial Support DMI-ENVIRO-HIRLAM project activities