Standard Surface Observations Research Articles

Central Arctic weather forecasting: Confronting theECMWF IFSwith observations from the Arctic Ocean 2018 expedition

AbstractForecasts with the European Centre for Medium‐Range Weather Forecasts' numerical weather prediction model are evaluated using an extensive set of observations from the Arctic Ocean 2018 expedition on the Swedish icebreakerOden. The atmospheric model (Cy45r1) is similar to that used for the ERA5 reanalysis (Cy41r2). The evaluation covers 1 month, with the icebreaker moored to drifting sea ice near the North Pole; a total of 125 forecasts issued four times per day were used. Standard surface observations and 6‐hourly soundings were assimilated to ensure that the initial model error is small. Model errors can be divided into two groups. First, variables related to dynamics feature errors that grow with forecast length; error spread also grows with time. Initial errors are small, facilitating a robust evaluation of the second group; thermodynamic variables. These feature fast error growth for 6–12 hr, after which errors saturates; error spread is roughly constant. Both surface and near‐surface air temperatures are too warm in the model. During the summer both are typically above zero in spite of the ongoing melt; however, the warm bias increases as the surface freezes. The warm bias is due to a too warm atmosphere; errors in surface sensible heat flux transfer additional heat from the atmosphere to the surface. The lower troposphere temperature error has a distinct vertical structure: a substantial warm bias in the lowest few 100 m and a large cold bias around 1 km; this structure features a significant diurnal cycle and is tightly coupled to errors in the modelled clouds. Clouds appear too often and in a too deep layer of the lower atmosphere; the lowest clouds essentially never break up. The largest error in cloud presence is aligned with the largest cold bias at around 1 km.

An Objective Detection Method for Convective Cold Pool Events and Its Application to Northern Africa

Abstract Convective cold pool events in (semi) arid areas have significant impacts on their environment. They reach horizontal extents of up to several hundred kilometers and the associated turbulence and shear can cause dust emissions and threaten aviation safety. Furthermore, cold pools play a major role in the organization of deep convection and in horizontal moisture transport. They have even been proposed to have impacts on larger-scale monsoon dynamics. Cold pools are not well represented in models using a convective parameterization. To test and improve these models, it is necessary to reliably detect cold pool occurrence from standard observational data. Former studies, however, focused on single cases or short time periods. Here, an objective and automated method for the generation of multiyear climatologies of cold-pool events is presented. The algorithm combines standard surface observations with satellite microwave data. Representativeness of stations and influence of their spatial density are addressed by comparison to a satellite-only climatology. Applying this algorithm to data from automatic weather stations and manned synoptic stations in and south of the Atlas Mountains in Morocco and Algeria reveals the frequent occurrence of cold pool events in this region. On the order of six cold-pool events per month are detected from May to September when the Saharan heat low is in its northernmost position. The events tend to cluster into several-days-long convectively active periods, often with strong events on consecutive days. The algorithm is flexible enough to be applied in comparable regions around the world.

High resolution re-analysis for the Baltic Sea region during 1965–2005 period

Regional reanalysis database BaltAn65+ comprising meteorological data for Baltic Sea region for the time period 1965–2005 is described. For data assimilation and hindcasts, the numerical weather prediction model HIRLAM 7.1.4 is applied, with 11 km horizontal and 60-layer vertical resolution. Reanalysis includes three-dimensional weather analysis data. Standard surface observations and meteorological soundings together with ship and buoy measurements from WMO observational network are used in analysis. Boundary fields are obtained from ECMWF ERA-40 global re-analysis. The BaltAn65+ can be considered as a regional refinement of ERA-40 for Baltic Sea region, providing the historical weather and climate data with enhanced spatial resolution, which is main motivation for creation of this novel reanalysis database.

Relationships between Gulf of California Moisture Surges and Tropical Cyclones in the Eastern Pacific Basin

Abstract Relationships between Gulf of California moisture surges and tropical cyclones (TCs) in the eastern Pacific basin are examined. Standard surface observations are used to identify gulf surge events at Yuma, Arizona, for a multiyear (July–August 1979–2001) period. The surges are related to TCs using National Hurricane Center 6-hourly track data for the eastern Pacific basin. Climate Prediction Center (CPC)- observed daily precipitation analyses and the NCEP Regional Reanalysis are used to examine the relative differences in the precipitation, atmospheric circulation, and moisture fields for several categories of surge events, including those that are directly related to TCs, indirectly related to TCs, and not related to TCs. It is shown that the response to the surge in the southwestern United States and northwestern Mexico is strongly discriminated by the presence or absence of TCs. Surges related to TCs tend to be associated with much stronger and deeper low-level southerly flow, deeper plumes of tropical moisture, and wetter conditions over the core monsoon region than surges that are unrelated to TCs. The response to the surge is also strongly influenced by the proximity of the TC to the Gulf of California (GOC) region. Tropical cyclones that track toward the GOC region exert a stronger, more direct influence on Yuma surges than those that track away from the GOC.

Relationships between Gulf of California Moisture Surges and Precipitation in the Southwestern United States

Abstract Relationships between Gulf of California moisture surges and precipitation in the southwestern United States are examined. Standard surface observations are used to identify gulf surge events at Yuma, Arizona, for a multiyear (July–August of 1977–2001) period, and Climate Prediction Center (CPC) precipitation analyses and NCEP–NCAR reanalysis data are used to relate the gulf surge events to the precipitation and atmospheric circulation patterns, respectively. Emphasis is placed on the relative differences in the precipitation and atmospheric circulation patterns for several categories of surge events, including those that are relatively strong (weak) and those that are accompanied by relatively wet (dry) conditions in Arizona and New Mexico after onset. It is shown that rapid surface dewpoint temperature increases are not necessarily a good indicator of increased rainfall in the region. The extent to which the precipitation and atmospheric circulation patterns are influenced by a phasing of tropi...

The Relationship between Tropical Easterly Waves and Surges over the Gulf of California during the North American Monsoon

Abstract Coastally trapped disturbances, which occur over the Gulf of California and are commonly referred to as gulf surges, are an important mechanism in the transport of low-level moisture into the southwestern United States. To determine whether or not gulf surges develop in association with the passage of tropical easterly waves, as hypothesized in previous studies, standard surface observations and European Centre for Medium-Range Weather Forecasts reanalysis data during the months of July and August over a 14-yr period are examined. Results indicate that tropical easterly wave troughs often cross western Mexico 1–3 days prior to surge onset at Yuma, Arizona, indicating a strong correlation between these two events. This analysis documents yet another mechanism by which the Tropics influences convection in the midlatitudes.

Bulk models of solar radiation at sea

With a view to improving climate prediction, we test various models for estimating solar radiation at sea from standard meteorological surface observations against long series of radiation measurements at several Ocean Weather Stations and at an offshore island meteorological station. The widely-used Budyko formula is found to err by up to 32% in estimating long-term mean insolation, and has even larger errors in reproducing seasonal variations. Various models which estimate solar radiation from solar elevation and from hourly cloud amount and type, using empirical or simple physical formulae, are evaluated. None of these models estimate mean insolation better than an existing formula which relies only on noon solar elevation and daily mean cloud amount, although the hourly models do reproduce seasonal, monthly and daily variations better. None of the formulae using standard surface observations is able to achieve the 10 Wm−2 accuracy in long-term mean insolation which is required for climate prediction.

Bulk models of solar radiation at sea

AbstractWith a view to improving climate prediction, we test various models for estimating solar radiation at sea from standard meteorological surface observations against long series of radiation measurements at several Ocean Weather Stations and at an offshore island meteorological station. The widely‐used Budyko formula is found to err by up to 32% in estimating long‐term mean insolation, and has even larger errors in reproducing seasonal variations. Various models which estimate solar radiation from solar elevation and from hourly cloud amount and type, using empirical or simple physical formulae, are evaluated. None of these models estimate mean insolation better than an existing formula which relies only on noon solar elevation and daily mean cloud amount, although the hourly models do reproduce seasonal, monthly and daily variations better. None of the formulae using standard surface observations is able to achieve the 10 Wm−2 accuracy in long‐term mean insolation which is required for climate prediction.

Nocturnal radiation measurements in Nigeria

Experimental work was carried out to determine the net flux of the long-wave radiation from the earth's surface to the atmosphere for clear nights in Nsukka, Nigeria. Values of the effective sky temperature were also obtained. The experimental radiator consisted of a flat mild steel plate coated with high emissivity black enamel paint. Data were obtained for the months of February through May. This seasonal period is free from the harmattan dust haze which characterizes part of the dry season and is free from the rain-bearing clouds of the wet season. A comparison of the measured downward flux of the atmospheric radiation was made with the data generated from the empirical formulas of some investigators using standard surface observations. Generally, the theoretical models yielded values that are lower than the observed results. However, the analytical values derived from Idso and Jackson's empirical model gave the best agreement with the experimental data. Agreement was within 0–5 per cent. The effective sky temperatures obtained are on the average 12.2°C less than the surface air temperatures. This was in close agreement with the result of Exell for the tropical climate of Thailand. The overall results presented are suitable for use in Nigeria and other regions with similar tropical or near-equatorial climate.