Abstract:Spatial correlations in the annual rainfall anomalies are analyzed using principal component analysis (PCA). Cross correlation analysis and composites are used to measure the influence of sea-surface temperature anomalies (SSTAs) in the tropical Atlantic (TA) and the tropical Pacific Ocean on the seasonal rainfall in Suriname. It is shown that the spatial and time variability in rainfall is mainly determined by the meridional movement of the inter-tropical convergence zone (ITCZ). The rainfall anomalies are fairly uniform over the whole country. The strongest correlation in the December-January rainfall (short wet season) at station Cultuurtuin is found to occur with the SSTAs in the Pacific region and is about c k Nino 1+2 = 0.59 at lag 1 month. In the March-May rainfall (beginning of the long wet season), there is a lagged correlation with the SSTAs in the Pacific region (c lag 3 Nino 1+2 = 0.59). The June-August rainfall (end of the long wet season) shows the highest correlation with SSTAs in the TSA region and is about c = −0.52 for lag 0. In the September-November long dry season there is also a lagged correlation with the TSA SSTAs of about c lag 3 = 0.66. These different correlations and predictors can be used for seasonal rainfall predictions.

[1] Weekly sonde observations in Suriname, supported by ECMWF analyses and a linear stability analysis, are used to analyze the recurrence of inert ial instability as the ITCZ migrates over land during the South American Monsoon. A layer of cool moist air from the Atlantic Ocean is then advected southward over Suriname in the shape of a cold front, displacing the warmer air over the continent. The return flow northward, by the upper branch of the Hadley cell, is a region where inertial instability pervades due to crossequatorial advection o f anticyclonic vorticity and the proximity of the subtropical jet as it migrates closer to the Equator. This unstable region evidently leads to the episodical formation of a meridional sub-cell below the tropopause, where the damping is calculated to be strong enough to stabilize flow at smaller vertical scales, and yet weak enough to allow the observed cell recurrence -at approximately the inertial frequency of the underlying latitudes. This instability should also contribu te to the Hadley cell formation thr ough northward acceleration in the upper branch. The moist saturated conditions in the lower troposphere do allow inertial instability here, but the high damping values within the boundary layer suggests that the observed southward acceleration in the lower branch of the Hadley cell has a cause other than inertial instability.

In climate research there is a strong need for accurate observations of water vapor in the upper atmosphere. Radiosoundings provide relative humidity profiles but the accuracy of many routine instruments is notoriously inadequate in the cold upper troposphere. In this study results from a soundings program executed in Paramaribo, Suriname (5.8°N, 55.2°W), are presented. The aim of this program was to compare the performance of different humidity sensors in the upper troposphere in the Tropics and to test different bias corrections suggested in the literature. The payload of each sounding consisted of a chilled-mirror "Snow White" sensor from Meteolabor AG, which was used as a reference, and two additional sensors from Vaisala, that is, either the RS80A, the RS80H, or the RS90. In total 37 separate soundings were made.For the RS80A a clear, dry bias of between Ϫ4% and Ϫ8% RH is found in the lower troposphere compared to the Snow White observation, confirming the findings in previous studies. A mean dry bias was found in the upper troposphere, which could be effectively corrected. The RS80H sensor shows a significant wet bias of 2%-5% in RH in the middle and upper troposphere, which has not been reported before. Comparing observations with RS80H sensors of different ages gives no indication of sensor aging or sensor contamination. It is therefore concluded that the plastic cover introduced by Vaisala to avoid sensor contamination is effective. Finally, the RS90 sensor yields a small but significant wet bias of 2%-3% below 7-km altitude.The time-lag error correction from Miloshevich et al. was applied to the Vaisala data, which resulted in an increased variability in the relative humidity profile above 9-(RS80A), 8-(RS80H), and 11-km (RS90) altitude, respectively, which is in better agreement with the Snow White data.The averaged Snow White profile is compared with the average profiles of relative humidity from the European Centre for Medium-Range Weather Forecasts (ECMWF). No significant bias is found in either the analyses or the forecasts. The correlation coefficient for the Snow White and ECMWF data between 200 and 800 hPa was 0.66 for the 36-h forecast and 0.77 for the analysis.

Abstract:Long-term changes and variability in river flows in the tropical Upper Suriname River Basin in Suriname (2-6°N, 54-58°W) are analysed, including the relation to sea surface temperatures (SSTs) in the tropical Atlantic and Pacific Ocean. To analyse variability, lag correlation and statistical properties of the data series are used. Long-term changes are analysed using parametric and non-parametric statistical techniques. The analyses are performed for the period 1952-1985. The results show that both river discharge series at Semoisie and Pokigron are non-stationary and have a negative trend. The negative rainfall trend in the centre of Suriname may be responsible for the negative trend in the annual river discharges in the basin. The highest correlation (Pearson's coefficient c) is obtained when the Tropical North Atlantic (TNA) SSTs lags the monthly discharges at Pokigron by 3-4 months (c D 0Ð7) and when the Tropical South Atlantic (TSA) SSTs lags the discharges by 4 months (c D 0Ð7). It also follows that the high (low) monthly flows, from April-August (September-March) are associated with increasing (decreasing) SSTs in the TNA and with decreasing (increasing) SSTs in the TSA. The results also reveal that years with low (high) discharges are more related to warmer (colder) SSTs during the year in the TNA region and a southward displacement of the Inter-Tropical Convergence Zone (ITCZ). However, the Pacific El Niño (La Niña) events may also be responsible for low (high) flow years in this basin.

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