Analyses & Numerical Prediction

Operations Bulletin No. 49
THE OPERATIONAL IMPLEMENTATION OF MESO_LAPS_PT125 IN NMOC
29 November 1999

INTRODUCTION

A new upgraded mesoscale prognosis system, called MESO_LAPS_PT125, was introduced into NMOC operations on the 16 November 1999. This new system has replaced both the South East and South West MESO_LAPS, which have been running in operations since May 1997. MESO_LAPS_PT125 was developed by the Regional Meteorology Group in BMRC, led by Dr. Kamal Puri and (during 1999) Dr. John McBride.

MESO_LAPS_PT125 (an acronym for "MESOscale Limited Area Prediction System PoinT 125") is basically a higher horizontal resolution (0.125⁰ latitude/longitude) configuration of the prognostic component in LAPS_PT375 (see APOB No 46). No separate assimilation, or analysis, occurs in the system. Its initial starting condition is derived directly from the LAPS_PT375 analysis. MESO_LAPS_PT125 is scheduled to start running after the completion of LAPS_PT375.

In its operational mode, MESO_LAPS_PT125 is run over a single domain covering the Australian region and incorporating the SE and SW domains of the superseded MESO_LAPS. Forecasts out to 36 hours are produced twice a day from 00 and 12UTC. Products from the system are available through DIFACS, MCIDAS, the real-time database ("rtdb") and the internal web.

OVERALL SCHEME

A simplified view of the operational structure of MESO_LAPS_PT125 is shown in Figure 1. The analysis from LAPS_PT375, interpolated to the 0.125⁰ latitude/longitude grid, provides the initial condition for MESO_LAPS_PT125. LAPS_PT375 also provides the lateral boundary conditions. Absolute values of mean sea level pressure, wind components, temperatures and mixing ratios (from LAPS_PT375) are used at 3-hourly intervals during the nesting procedure. The pre-processor (in Figure 1) generates 'windowed' versions of the LAPS_PT375 and other data (including SSTs and soil moisture) and prepares the initial and boundary conditions for use by the prognosis model.

As noted in APOB No 46, the prognosis component is based on a hydrostatic primitive equation model formulated on sigma levels for a non-staggered (Arakawa "A") latitude/longitude grid. Physical parameterisations include: a mass-flux convective scheme (for deep, mid-level and shallow convection), large-scale rain, radiative transfer with a diurnal cycle, diagnostic clouds, stability-dependent surface fluxes and interactive soil moisture. The land-surface scheme provides a detailed vegetation and soil-type specification and improved soil moisture initialisation.

FIGURE 1. Schematic representation of the operational structure of MESO_LAPS_PT125.

OPERATIONAL CONFIGURATION

(i) Domain: 4.875⁰N-55.0⁰S, 95.0⁰E-169.875⁰E (see Figure 2)

(ii) Horizontal resolution: 0.125⁰ (480x600) latitude/longitude grid (Figure 3 shows the horizontal resolution of the grid in the Perth region)

(iii) Vertical resolution: No. of sigma levels=29

Levels=0.9988, 0.9974, 0.9943, 0.9875, 0.9750, 0.9625, 0.9500, 0.9250, 0.9000, 0.8750, 0.8500, 0.8000, 0.7500, 0.7000, 0.6000, 0.5000, 0.4500, 0.4000, 0.3500, 0.3000, 0.2750, 0.2500, 0.2250, 0.2000, 0.1750, 0.1500, 0.1000, 0.0700, 0.0500 Figure 4 shows the vertical level distribution of levels and Table 1 gives the approximate heights for each of the levels.

(iv) Topography: as shown in Figure 2 (derived from a 0.1⁰ resolution data set)

(v) Initialisation: digital filtering technique

(vi) Timesteps: 10 seconds for dynamics, 240 seconds for physics

(vii) Nesting: lateral boundary conditions derived from +3 to +36 hour LAPS_PT375 forecasts

(viii) Climatology: albedo

(ix) Soil Moisture Analysis: Daily 0.25⁰x 0.25⁰

(x) Sea Surface Temperature Analysis: Weekly 1⁰x1⁰

(xi) Output: hourly single-level and 3-hourly multi-level forecasts out to 36 hours from 00 UTC and 12 UTC (or, more correctly, 23 and 11UTC) daily

FIGURE 2. Full domain of MESO_LAPS_PT125 and associated topography.

(xii) NEC SX-4 supercomputer resources:

36 hour prognosis:- elapsed time: 70 minutes (approx.), number of processors: 16,

memory: 4.9GB

(xiii) NMOC products reliant on MESO_LAPS_PT125:

Seastate model (WAM): driven by 10 m boundary layer winds

Meteograms

EER

(xiv) Feed-back: Comments on MESO_LAPS_PT125 can be mailed to:

laps_feedback@bom.gov.au

FIGURE 3. A sub-domain (over Perth) showing the horizontal 0.125⁰ latitude/longitude grid.

FIGURE 4. Vertical level distribution in MESO_LAPS_PT125.

TABLE 1.Approximate heights corresponding to sigma () levels in MESO_LAPS_PT125.

SYNOPTIC PERFORMANCE

Terry Skinner (MSDSS, NMOC) undertook a synoptic assessment of MESO_LAPS_PT125 for the period: August 1999 - November 1999, looking at the mean sea level pressure, low level wind and rainfall prognosis products. The following features, both positive and negative, emerged from the assessment:

Mean Sea Level Pressure Prognoses:

. Broadscale features are well captured (eg the frontal systems associated with inland prefrontal troughs moving across SE Australia have good timing and amplitude).

. Development of cut off lows are well forecast over the Tasman Sea and Bight, although there is a positive bias (<5 hPa) in central pressure. (The devopment of a "bomb" off the NSW coast from an easterly dip over Queeensland on the 8-9 November 1999 was particularly good).

. Anticyclone centres in Bight and Indian Ocean are generally well placed, but show a negative bias (~2 hPa) in central pressure.

. Unsmoothed fields over both the ocean and land, particularly north of 35⁰S, tend to show noisy meteorological structure.

. An occasional positive pressure bias over Northern Queensland particularly at +36 hours, results in a poor representation of Queensland heat trough (ie the trough does not show sufficient amplitude).

. WA trough is reasonably well forecast, but there is a tendency to oversharpen the trough at +36 hours.

. Kimberley heat low is occasionally misplaced, due to positive pressure bias over Northern Kimberley region.

10 m Wind Forecasts:

Vector wind fields appear to be realistic, but wind speeds over land are too light.

Rainfall Predictions:

. Major rainbands associated with broadscale features, such as frontal systems and upper troughs, are well indicated with good orientation and area.

. 12-36 hour forecasts show a negative bias, ie a severe underprediction of the area of rainfall especially with falls of < 10 mm/day; heavy rainfall rates in the tropics (50-100 mm/day) are occasionally missed, especially in the Kimberley region and the Top End.

. 0-24 hour maximum rainfall rates, especially in the tropics, are sometimes overpredicted.

. Light rainfall rates (<10 mm/day) are, on occasion, missed at 0-24 hours, especially in stream weather on NSW, Victorian and Tasmanian coasts; however, non-frontal spurious areas of rainfall (< 10 mm/day) are occasionally forecast over Queensland and WA interior.

. Heavy tropical falls in Northern Queensland can be misplaced.

. Orographic rainfall along Queensland coast are occasionally overforecast.

PRODUCT AVAILABILITY

DIFACS

MESO_LAPS_PT125 currently uses the Difacs slots: 864 - 892 as follows:

864 - 867: Mean Sea Level Pressure (00, +12, +24, +36 hr)

868 - 870: Precipitation ( +12, +24, +36 hr)

871 - 873: 850 hPa (+12, +24, +36 hr)

874 - 876: 850 hPa Dew Point (+12, +24, +36 hr)

877 - 879: 700 hPa Vertical Motion (+12, +24, +36 hr)

880 - 892: 10 m Wind (00, +03, +06, +09, +12, +15, +18, +21, +24, +27, +30, +33, +36 hr)

(Slots 410 - 413 will soon be used for a set of combined Mean Sea Level Pressure/Thickness charts.)

It is noted that Difacs charts are also available through the web,

REAL-TIME DATABASE:

Both sigma and pressure level gridded data, from MESO_LAPS_PT125, are written to the real-time database (rtdb). Initial condition and forecast fields (out to +36 hours) are available for the full domain. The database is currently constrained to hold MESO_LAPS_PT125 fields for the last day only.

As already stated, MESO_LAPS_PT125 runs on a 480x600 horizontal grid and on 29 sigma levels in the vertical. However, in view of resource limitations (both in terms of CPU power and disc storage), the multi-level (and some single-level) fields are put into NMOC's real-time database (ie rtdb) at a coarse horizontal resolution of 240x300 and only a small number of other single-level fields are put into rtdb at the full horizontal resolution of 480x600 (see Figure 5). Tables 2 and 3 show the various MESO_LAPS_PT125 fields available through rtdb.

For completeness, the characteristics of the rtdb dataset are as follows:

model_type=MESO_LAPS_PT125

dset_name=yyyymmddhh.aus

and the 4 geometry names:

geom_name=australia_240x300 (ie 0.25⁰ grid covering the full domain - see Table 2)

geom_name=australia_480x600 (ie 0.125⁰ grid covering the full domain - see Table 3)

geom_name=seaustralia_120x160 (ie 0.25⁰ grid covering the old SE MESO_LAPS domain)

geom_name=swaustralia_120x160 (ie 0.25⁰ grid covering the old SW MESO_LAPS domain)

However, the last two, covering the superseded SE and SW MESO_LAPS domains, will eventually be discontinued.

FIGURE 5. Schematic diagram showing product resolution and availability for

MESO_LAPS_PT125.

MCIDAS:

All the fields listed in Tables 2 and 3 can be accessed directly by using the MCIDAS ADDE method. The relevant dataset names, corresponding to the 4 geometry names above, are:

MESO-P125

MESO-P125-HR

MESO-P125-SE

MESO-P125-SW

(Again, for the interim, and in addition to the last 2 dataset names above, the GRID1700 series of MCIDAS files will continue to be generated, but with MESO_LAPS_PT125 as the source.)

TABLE 2. MESO_LAPS_PT125 fields in NMOC's real-time database (rtdb) - coarse resolution representation.

Horizontal grid: 240x300

29 Vertical sigma levels (ie sgma_lvl): 0.9988, 0.9974, 0.9943, 0.9875, 0.9750, 0.9625, 0.9500, 0.9250, 0.9000, 0.8750, 0.8500, 0.8000, 0.7500, 0.7000, 0.6000, 0.5000, 0.4500, 0.4000, 0.3500, 0.3000, 0.2750, 0.2500, 0.2250, 0.2000, 0.1750, 0.1500, 0.1000, 0.0700, 0.0500

13 Vertical pressure levels (ie isbr_lvl): 1000, 950, 900, 850, 700, 500, 400, 300, 250, 200, 150, 100, 50 hPa (Note: Dew point temperatures are only ingested to 300hPa.)

Time levels: 3-hourly from 00 to +36 (at 11 and 23UTC)

# isbr_lay (500)

TABLE 3. MESO_LAPS_PT125 fields in rtdb - high (ie full) resolution representation.

Horizontal grid: 480x600

At present, only single level fields are ingested at high resolution.

Time levels: 1-hourly from 00 to +36 (at 11 and 23UTC)

FIGURE 6. 24-hour forecast of mid-level cloud amount over the full domain of MESO_LAPS_PT125.

FIGURE 7. 36-hour forecast of screen temperature over an Adelaide sub-domain.

WEB:

A large number of MESO_LAPS_PT125 products are available through the Bureau's internal web.

-> MESO_LAPS_PT125 Displays

-> LATEST REAL-TIME CHARTS

-> Domain of choice

-> Product choice from table

The link "USER DEFINED CHARTS (INTERACTIVE ACCESS)" is currently being set up to use the newly available display package METVIEW running directly off the real-time database.

Figures 6 and 7 give examples of the types of products available from the web.

ARCHIVES

Data from MESO_LAPS_PT125 is archived on SAM-FS (in NetCDF form)

FUTURE DEVELOPMENTS

The migration of MESO_LAPS_PT125 to the new NEC SX-5 (on its arrival) and the operational implementation of MESO_LAPS_PT050, for the Sydney and Melbourne regions, are the immediate plans for the mesoscale system in NMOC. In addition, a new urban Air Quality Forecast system will be associated with the 0.05⁰ version. Ongoing improvements to the model itself include the Semi-Lagrangian Semi-Implicit (SLSI) and non-hydrostatic formulations and better parameterisation of moist processes. In the longer term, it is planned to introduce a mesoscale analysis system.

REFERENCE

Puri, K., Dietachmayer, G., Mills, G.A., Davidson, N.E., Bowen, R.A., and Logan, L.W.: "The new BMRC Limited Area Prediction System, LAPS." Australian Meteorological Magazine Vol 47, No 3, 203-223, 1998.