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Mark R. Jury

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This observational study examines zonal gradients in the lower atmosphere and upper ocean across the windward Antilles during midsummer 2012. While earlier work reported on meridional confluence, here the focus is on the zonal enrichment of trade winds by upstream shallow seas and islands. Intercomparisons along 18.2°N are made between modern reanalysis and satellite estimates, and coastal station, moored buoy, aircraft, and radiosonde observations for one case and as a June–July 2012 average. Mean gradients per 100 km east of Puerto Rico were 0.2 g kg−1 for 925-hPa specific humidity, 0.16°C for SST, 0.01 m for sea level, and 2.0 × 10−3 g kg−1 for cloud water. Zonal changes in the lower atmosphere occur in three stages: 1) Atlantic, where westward ocean currents, strong trade winds, and subsidence prevail; 2) Antilles, where ocean currents diminish and sea temperatures increase; and 3) island, where trade winds abate [−1 m s−1 (100 km)−1] and diurnal evapotranspiration greater than 10 mm day−1 offsets large-scale subsidence producing a localized convection.

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Mark R. Jury

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This study analyzes a convective outbreak over the Red Sea on 25 August 2009 that generated easterly waves over the Sahel, floods in Ouagadougou, and a hurricane in the east Atlantic. The convective outbreak occurred on the equatorward flank of the African easterly jet 18°–22°N and associated meridional heating gradients over the Arabian Peninsula. The Rift Valley mountains induced a vertical orographic undulation and cyclonic perturbation. Two thunderstorm clusters over the southern Red Sea received moist inflow from the Ethiopian highlands and northern Red Sea. This group of three easterly waves intensified downstream over the Sahel. One of the convective triggers was enhancement of the Arabian Ridge by the northern subtropical jet. Statistical analyses indicate that African easterly waves and subsequent tropical storms are more influenced by upstream kinematic shear than thermodynamic energy. The work offers new insights on the formation of easterly waves over the northern Rift Valley.

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Mark R. Jury

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This study examines the spatial variability of mean annual rainfall in the Caribbean in the satellite era 1979–2000. Intercomparisons of gridded rainfall fields from conventional stations, satellite estimators, reanalysis products, and coupled general circulation models (CGCMs) are made, with a focus on the Antilles island chain and their land–sea transitions. The rainfall products are rated for their ability to capture a number of key features, including (i) topographically enhanced precipitation over the larger western Antilles islands of Cuba, Jamaica, Hispanola, and Puerto Rico; (ii) the rain shadow west of Hispanola; (iii) the two dry zones where SSTs are low: north of Venezuela and north of the Lesser Antilles; and (iv) the wet axis extending north of Trinidad. The various monitoring and modeling systems produce gridded rainfall fields at resolutions from 50 to 280 km, from station reconstructions, satellite estimates, blended and reanalysis products, and CGCM climatologies with respect to surface forcing fields. Wet and dry biases were found in many of the reanalysis and satellite products, respectively—either over the whole Caribbean or in a certain sector. The intercomparison found some measure of consensus, but no single product is without discrepancy. High-resolution passive microwave satellite rainfall estimates [Climate Prediction Center’s multisaltellite passive microwave, IR morphed product (cMOR)] appear “most representative”; however, the climatology is short (2003–07) and the field is generally drier than the consensus. Of the conventional products, decadal variability of climate interpolated rain gauges (DEKL), World Climate Research Programme’s (WCRP) blended rain gauges, the Comprehensive Ocean–Atmosphere Data Set (COADS), and an operational climate anomaly monitoring system of NCEP (CAMS) perform well. Among the satellite estimators, the Global Precipitation Climatology Project’s blended gauge and IR satellite (GPCP) and outgoing longwave radiation (OLR) capture the key features and ocean–island transitions. The Center for Ocean–Land–Atmosphere Studies [COLA; the coupled model, part of the Coupled Model Intercomparison Project (CMIP, phase 3)] and the climate forecast system of the NCEP (CFS) models perform reasonably, but NCAR’s Parallel Climate Model (PCM; the CGCM’s historical run of CMIP3) fares poorly. The version 2 hindcast of the operational Medium-Range Forecast (MRF) weather prediction model (REAN) captures the smaller wet zones and topographically enhanced features, but it does not handle the broad oceanic dry zones well, as the input from the operational climate data assimilation system of NCEP (CDAS) has a wet bias. Of the various key rainfall features, high rainfall over southern Cuba and the rain shadow west of Hispanola are poorly handled by most products. The wet axis north of Trinidad and the dry zone north of Venezuela are well represented in many climatologies.

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Mark R. Jury

Abstract

Ocean and atmosphere reanalysis fields are used to study environmental conditions and their relation to commercial fish catch in the central Benguela upwelling zone, using both targeted and objective techniques. Composite maps and sections indicate a 10%–20% weakening of southeasterly winds, a 0.5°C warming of sea temperatures over the shelf, and changes in currents and subsurface upwelling associated with higher fish catch. During periods of high fish catch, recirculating gyres form that may aid the retention of eggs and larvae. Offshore winds contribute to poleward Ekman transport in a 50-m-deep layer within 100 km of the coast.

In addition to composite analysis, the natural variability is studied by principal component analysis of wind stress, sea level, temperature, salinity, currents, and vertical motion in the period 1970–2007. Comparison of interannual time scores and fisheries data indicate that anomalous poleward winds and warmer temperatures in the Lüderitz plume, driven by an atmospheric trough in the South Atlantic, are associated with higher catch rates.

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Mark R Jury

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This study compares different methods of predicting crop-related climate in the Ethiopian highlands for the period 1979–2009. A target index (ETH4) is developed as an average of four variables in the June–September season—rainfall, rainfall minus evaporation, estimated latent heat flux, and vegetation, following correlation with crop yields at Melkassa, Ethiopia (8.4°N, 39.3°E, 1550 m elevation). Predictors are drawn from gridded near-global fields of surface temperature, surface air pressure, and 200-hPa zonal wind in the preceding December–March season. Prediction algorithms are formulated by stepwise multivariate regression. The first set of predictors derive from objective principal component (PC) time scores with tropical loading patterns, and the second set is based on key areas determined from correlation with the target index. The second PC of upper zonal wind reveals a tropical–subtropical dipole that is correlated with ETH4 at two-season lead time (correlation coefficient r = −0.53). Point-to-field regression maps show high-latitude signals in surface temperature (positive in North America and negative in Eurasia) and air pressure (negative in the North Pacific Ocean and positive in the South Pacific). Upper zonal winds are most strongly related with ETH4 over the tropical Pacific and Africa at two-season lead time. The multivariate algorithm that is based on PC predictors has an adjusted r 2 fit of 0.23, and the algorithm using key-area predictors achieves r 2 = 0.37. In comparison, numerical model forecasts reach r 2 = 0.33 for ECMWF simulations but are low for other models. The statistical results are specific to the ETH4 index, which is a climate proxy for crop yields in the Ethiopian highlands.

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Mark R. Jury

Abstract

This study considers eastern Antilles (11°–18°N, 64°–57°W) weather and climate interactions in the context of the 2013 Christmas storm. This unseasonal event caused flash flooding in Grenada, St. Vincent, St. Lucia, Martinique, and Dominica from 24 to 25 December 2013, despite having winds <15 m s−1. The meteorological scenario and short-term forecasts are analyzed. At the low level, a convective wave propagated westward while near-equatorial upper westerly winds surged with eastward passage of a trough. The combination of tropical moisture, cyclonic vorticity, and uplift resulted in rain rates greater than 30 mm h−1 and many stations reporting 200 mm. Although forecast rainfall was low and a few hours late, weather services posted flood warnings in advance. At the climate scale, the fresh Orinoco River plume brought into the region by the North Brazil Current together with solar radiation greater than 200 W m−2, enabled sea temperatures to reach 28°C, and supplied convective available potential energy greater than 1800 J kg−1. Climate change model simulations are compared with reference fields and trends are analyzed in the eastern Antilles. While temperatures are set to increase, the frequency of flood events appears to decline in the future.

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Mark R. Jury

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Hydrological fluctuations of Malawi’s Shire River and climatic drivers are studied for a range of time and space scales. The annual cycles of basin rainfall and river flow peak in summer and autumn, respectively. Satellite and model products at <50-km resolution resolve the water deficit in this narrow valley. The leading climate index fitting Shire River flow anomalies is the Climatic Research Unit (CRU) Palmer drought severity index, based on interpolated gauge rainfall minus Penman–Monteith potential evapotranspiration. Climate variables anticipate lake level changes by 2 months, while weather variables anticipate river flow surges by 2 days. Global climate patterns related to wet years include a Pacific La Niña cool phase and low pressure over northeastern Africa. Shire River floods coincide with a cyclonic looping wind pattern that amplifies the equatorial trough and draws monsoon flow from Tanzania. Hot spells are common in spring: daytime surface temperatures can reach 60°C causing rapid desiccation. An anticyclonic high pressure cell promotes evaporation losses of ~20 mm day−1 over brief periods. Flood and drought in Malawi are shown to be induced by the large-scale atmospheric circulation and rainfall in the surrounding highlands. Hence, early warning systems should consider satellite and radar coverage of the entire basin.

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Mark R. Jury

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This study considers tropical cyclones Irene in Puerto Rico from 2011 and Isaac in the Dominican Republic from 2012. Impacts trailed more than a day after the storm in both cases. Irene passed Puerto Rico on 22 August 2011, yet bands of heavy rainfall caused floods and disruption on 23 August. In the second case, Isaac passed Hispaniola on 24 August 2012, but stormy weather continued on 25 August. Onshore winds, 4-m waves, and associated tides and river outflow closed the harbor of Santo Domingo. Emergency managers and maritime operators should be aware of the delayed impacts of tropical cyclones in the Caribbean Sea region.

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Mark R. Jury

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The concentration of trace gases and aerosols in Ethiopia is poorly characterized due to a limited history of surface measurements. Here, satellite measurements and model estimates of atmospheric composition are employed to understand space–time distributions in the period 2000–16. Methane (CH4) and carbon monoxide (CO) display high concentrations over the highlands and provide a focus for analysis of monthly and daily data. CH4 emissions from livestock peak at the beginning of the dry season, while CO from biomass burning rises at the end of the dry season. The seasonal cycle of dust, aerosol optical depth (AOD), and CO2 is inversely related with CH4, while CO closely follows sensible heat flux, thus linking drying and rural biomass burning. Stable easterly flow in the dry season accumulates local emissions, so near-surface concentrations of CO and CH4 are high then. The weather pattern underlying an episode of high nitrogen dioxide (NO2) concentrations was studied. In addition to a stable lapse rate and dry anticyclonic weather, midtropospheric subsidence was related to intrusion of the northern subtropical jet stream on 24–26 December 2010. The wind shadow was cast by the Rift Escarpment limited dispersion, particularly with the dry, stable weather conditions. A key outcome of this work is that CH4 concentrations over Ethiopia are high in global context and have increased >0.1 ppm from 2002 to 2016; hence, there is a need to improve livestock management and production efficiency.

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Mark R. Jury

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This study reconsiders the role of the Agulhas Current in South African climate variability. Here, the Agulhas Current is delimited by its anticyclonic looping flow and cluster analysis of detrended SST anomalies that lead to an area 28°–37°S, 18°–35°E, poleward of South Africa. Regression of detrended Agulhas SST with rainfall anomaly fields in the years 1950–2012 yields a surprising negative influence over the interior. In summer, the negative regression exhibits a northwest axis consistent with reduced cloud band activity. Positive influence is confined to the eastern escarpment in the September–November season when cutoff lows are prevalent. The overall negative influence of the Agulhas SST is confirmed by regression with the vegetation fraction and latent heat flux in the satellite era.

Mechanisms of South African rainfall suppression were investigated. The Agulhas SST index is positively related to the multivariate ENSO index at the 1–3-month lead time. Hence, warm years in the Agulhas Current follow Pacific El Niño. Composite ocean analysis shows enhanced westerly winds offshore and a westward extension of warm salty water from the anticyclonic south Indian Ocean gyre. Composite atmospheric analysis exhibits moist uplifted air over the Agulhas Current folding into an equatorward circulation that sinks over the interior plateau. Because Agulhas SST partially follows ENSO, its suppression of interior rainfall is concluded to be passive.

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