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Siebren de Haan
and
Ad Stoffelen

Abstract

In this paper the beneficial impacts of high-resolution (in space and time) wind and temperature observations from aircraft on very short-range numerical weather forecasting are presented. The observations are retrieved using the tracking and ranging radar from the air traffic control facility at Schiphol Airport, Amsterdam, the Netherlands. This enhanced surveillance radar tracks all aircraft in sight every 4 s, generating one million wind and temperature observations per day in a radius of 270 km around the radar. Nowcasting applications will benefit from improved three-dimensional wind fields. When these observations are assimilated into a numerical model with an hourly update cycle, the short-range three-dimensional wind field forecasts match the observations better than those from an operational forecast cycle, which is updated every 3 h. The positive impact on wind in the first hours of the forecast gradually turns into a neutral impact, when compared to other wind and temperature observations. The timeliness of the forecasts combined with the high resolution of the observations are the main reasons for the observed nowcasting benefits. All in all, the assimilation of high-resolution wind (and temperature) observations is found to be beneficial for nowcasting and short-range forecasts up to 2–3 h.

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Siebren de Haan
and
Siebe H. van der Veen

Abstract

The Nowcasting Satellite Application Facility (NWC SAF) cloud mask from the Meteosat Second Generation (MSG) satellite is introduced in the initialization step of an hourly Rapid Update Cycle (RUC) of the High Resolution Limited Area Model (HIRLAM). MSG cloud-top temperatures and synoptic cloud-base height information are combined at analysis time. This cloud initialization scheme is applied to an experimental run, which is a copy of the operational Royal Netherlands Meteorological Institute [Koninklijk Nederlands Meteorologisch Instituut (KNMI)] RUC model. The experimental run was employed during the period June–December 2011. The RUC model has a forecast length of 6 h. Cloud cover forecasts are verified against MSG cloud cover information and synoptic observations. Forecasts of precipitation, surface pressure, 2-m temperature, and upper-air temperature are verified against synoptic observations and aircraft temperature observations. It is shown that including MSG cloud information in the RUC considerably improves the forecasts of most of these model fields, when compared to the operational control RUC. Both the bias and standard deviation of the errors of the cloud cover forecast are reduced substantially. Forecasts of light precipitation show a slight negative impact, but forecasts of heavy precipitation become better. The bias in 3D temperature fields disappears nearly completely. The error bias of 2-m temperatures has become larger. Two case studies are presented. The first case study had very good forecast performance with respect to low clouds when compared to the reference run. The second case study shows an ambiguous impact; there are still some deficiencies in the cloud initialization and cloud forecast when focusing on a single location.

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Siebren de Haan
,
Gert-Jan Marseille
,
Paul de Valk
, and
John de Vries

Abstract

Denial experiments, also denoted observing system experiments (OSEs), are used to determine the impact of an observing system on the forecast quality of a numerical weather prediction (NWP) model. When the impact is neutral or positive, new observations from this observing system may be admitted to an operational forecasting system based on that NWP model. A drawback of the method applied in most denial experiments is that it neglects the operational time constraint on the delivery of observations. In a 10-week twin experiment with the operational High-Resolution Limited-Area Model (HIRLAM) at KNMI, the impact of additional ocean surface wind observations from the Advanced Scatterometer (ASCAT) on the forecast quality of the model has been verified under operational conditions. In the experiment, the operational model was used as reference, parallel to an augmented system in which the ASCAT winds were assimilated actively. Objective verification of the forecast with independent wind observations from moored buoys and ASCAT winds revealed a slight improvement in forecast skill as measured by a decrease in observation-minus-forecast standard deviation in the wind components for the short range (up to 24 h). A subjective analysis in a case study showed a realistic deepening of a low pressure system over the North Atlantic near the coast of Ireland through the assimilation of scatterometer data that were verified with radiosonde observations over Ireland. Based on these results, the decision was made to include ASCAT in operations at the next upgrade of the forecasting system.

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Evert I. F. de Bruijn
,
Siebren de Haan
,
Fred C. Bosveld
,
Ben Wichers Schreur
, and
Albert A. M. Holtslag

Abstract

High-resolution upper-air wind observations are sparse, and additional observations are a welcome source of meteorological information. In this paper the potential of applying balloon flights for upper-air wind measurements is explored, and the meteorological content of this information is investigated. The displacement of a hot-air balloon is a measure for the wind speed and direction and thus a potential source for wind observations in the lower part of the troposphere. The response time of the balloon on the changing wind is fast in the beginning and levels off for smaller relative wind speeds. Four case studies are presented, and the balloon-derived winds are compared with other wind observations and with results from the HIRLAM–ALADIN Research on Mesoscale Operational NWP in Europe (HARMONIE) model. It turns out that hot-air balloon tracks can indeed produce useful wind observations just above and in the atmospheric boundary layer (ABL).

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