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Moisture Budgets (moisture + budget)
Selected AbstractsAtmospheric moisture budget over Antarctica and the Southern Ocean based on the ERA-40 reanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2008Hanna Tietäväinen Abstract The atmospheric moisture budget over Antarctica and the Southern Ocean was analysed for the period 1979,2001 on the basis of the ERA-40 reanalysis of the European Centre for Medium-Range Weather Forecasts. Meridional transport by transient eddies makes the largest contribution to the southward water vapour transport. The mean meridional circulation contributes to the northward transport in the Antarctic coastal areas, but this effect is compensated by the southward transport by stationary eddies. The convergence of meridional water vapour transport is at its largest at 64,68°S, while the convergence of zonal transport is regionally important in areas of high cyclolysis. Inter-annual variations in water vapour transport are related to the southern annular mode (SAM). The eastward transport has a significant (95% confidence level) positive correlation with the SAM index, while the northward transport has a significant negative correlation with SAM near 60°S. Hydrological balance is well-achieved in the ERA-40 reanalysis: the difference between the water vapour flux convergence (based on analysis) and the net precipitation (precipitation minus evaporation, based on 24-h forecasts) is only 13 mm yr,1 (3%) over the Southern Ocean and , 8 mm yr,1 (5%) over the continental ice sheet. Over the open ocean, the analysis methodology favours the accuracy of the flux convergence. For the whole study region, the annual mean flux convergence exceeded net precipitation by 11 mm yr,1 (3%). The ERA-40 result for the mean precipitation over the Antarctic continental ice sheet in 1979,2001 is 177 ± 8 mm yr,1, while previous estimates range from 173 to 215 mm yr,1. For the period 1979,2001, the ERA-40 data do not show any statistically significant trend in precipitation over the Antarctic grounded ice sheet and ice shelves. From the ERA-40 data, the annual average net evaporation (evaporation minus condensation) is positive over the whole continent. Copyright © 2008 Royal Meteorological Society [source] The impact of soil moisture modifications on CBL characteristics in West Africa: A case-study from the AMMA campaignTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S1 2010M. Kohler Abstract Within the framework of the AMMA campaign in 2006, the response of surface properties to precipitation and their effect on the state of the convective boundary layer (CBL) and on convective instability were analysed. The observation periods covered the pre-monsoon onset (SOP 1) and the mature monsoon phase (SOP 2) and were performed in southwest Burkina Faso. Precipitation caused a distinctive increase in the volumetric soil moisture content in the upper 20 cm of the soil. Coupled with the increase in soil moisture, a continuous decrease of surface and soil temperature with time was observed. Changes in surface temperature, albedo, and a higher availability of water affected the partitioning of the energy balance. Highest values of the Bowen ratio were found during SOP 1 when the surface was dry and vegetation sparse. In SOP 2, a higher vegetation cover made the albedo and Bowen ratio less sensitive to changes in soil moisture. Modifications of surface fluxes influenced the CBL conditions. The CBL height in SOP 1 was 1658 m and in SOP 2 877 m. The heat budget of the CBL was dominated by sensible heat flux convergence, whereas the moisture budget was controlled by both advection and latent heat flux convergence. It was confirmed by the measurements that the diurnal development of convective instability was dominated by the CBL evolution and controlled by changes in the mid- or upper troposphere to a minor degree only. Linear correlations were found between the near-surface equivalent potential temperature and both convective available potential energy and convection index. Copyright © 2009 Royal Meteorological Society [source] Spring northward retreat of Eurasian snow cover relevant to seasonal and interannual variations of atmospheric circulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2003Hiroaki Ueda Abstract An observational study is made of the seasonal and interannual variations of spring snow-disappearance over the Eurasian continent and the circulation mechanisms causing those variations. The spring northward retreat of the snow boundary over the East European Plain (EEP) between 30 and 60° E is faster (0.4° per day) than to the east of the Ural Mountain range (0.3° per day). These migrations of the snow boundary lag behind the appearance of the surface air temperature 0 °C by about 1 to 5 pentads. The analyses of the atmospheric heat and moisture budgets showed that the seasonal intrusion of warm air associated with southwesterly winds is primarily responsible for the rapid snowmelt in March and April over the EEP. In addition, the adiabatic heating of descending air plays a secondary role in the snowmelt in mid-March. On an interannual time scale, horizontal warm advection also plays an essential role in the spring northward retreat of snow cover extent. The present study confirms the previous finding that the surface air temperature anomalies, produced during the seasonal snow-disappearance period, diminished in May, suggesting a weak dynamical linkage between the EEP snow cover and Asian summer monsoon. Copyright © 2003 Royal Meteorological Society [source] Aircraft observations of cloud droplet number concentration: Implications for climate studiesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 602 2004I. Gultepe Abstract Droplet number concentration (Nd) is a major parameter affecting cloud physical processes and cloud optical characteristics. In most climate models, Nd is usually assumed to be constant or a function of the droplet and aerosol number concentration (Na). Three types of cloud systems over Canada, namely Arctic clouds, maritime boundary-layer clouds, and winter storms, were studied to obtain values of Nd as a function of temperature (T). The probability density function of Nd was also calculated to show the variability of this parameter. The results show that Nd reaches a maximum at about 10 °C (200 cm,3) and then decreases gradually to a minimum (,1,3 cm,3) at about ,35°C. A comparison of relationships between Nd and Na indicates that estimates of Nd from Na can have an uncertainty of about 30,50 cm,3, resulting in up to a 42% uncertainty in cloud short-wave radiative forcing. This study concludes that the typical fixed values of Nd, which are ,100 cm,3 and ,200 cm,3 for maritime and continental clouds, respectively, and the present relationships of Nd to Na, could result in a large uncertainty in the heat and moisture budgets of the earth's atmosphere. It is suggested that the use of relationships between Nd and T can improve climate simulations. © Crown copyright, 2004. Royal Meteorological Society [source] Comparing mass-consistent atmospheric moisture budgets on an irregular grid: An Arctic exampleTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 592 2003M. Göber Abstract We present a method to minimize the effects of different resolution and mass imbalance when comparing atmospheric energy and water budgets from different datasets. Sizeable differences between re-analysis- and radiosonde-based atmospheric budgets had been found in earlier studies and it had been suspected that the different resolutions of the datasets strongly contributes to these discrepancies. Furthermore, most studies so far had used mass-imbalanced wind fields, which can lead to serious errors. We balance the wind field by using a variational modification algorithm combined with a finite-element discretization which allows the use of data on a grid defined by the radiosonde network. This method permits the computation of flux divergences in integral form and gives a consistent numerical method to get a mass-balanced wind field with minimum modifications. Applying this method to Arctic radiosonde and re-analysis data on the same grid leads to a better agreement with respect to the horizontal distribution and the mean annual cycle of the moisture flux convergence. The constraint of mass balance on the wind field leads to a greatly reduced and more realistic variability in space and time. However, a systematic difference of about 20% remains between the estimate based on a re-analysis dataset sampled only on the coarse grid of the radiosonde network and an estimate based on the use of the full, fine grid of the re-analysis. These systematic differences can be significantly reduced by creating a simulated radiosonde dataset from the re-analysis with doubled resolution. We undertake an extensive analysis of the uncertainty of the estimates originating from the choices made in the specification of the algorithm. Based solely on radiosonde data, which are likely to result in a low bias, we estimate the net water gain of the Arctic atmosphere as 164 ± 10 mm yr,1 (0.45 ± 0.03 mm d,1) for 1979,93. Copyright © 2003 Royal Meteorological Society. [source] | ||||||||||