scholarly journals Observations of Cloud, Radiation, and Surface Forcing in the Equatorial Eastern Pacific

2008 ◽  
Vol 21 (4) ◽  
pp. 655-673 ◽  
Author(s):  
C. W. Fairall ◽  
Taneil Uttal ◽  
Duane Hazen ◽  
Jeffrey Hare ◽  
Meghan F. Cronin ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Surface Flux ◽  
Cloud Fraction ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Cloud Base ◽  
Tropical Eastern Pacific ◽  
Cloud Forcing ◽  
The North

Abstract In this paper the authors report on a study of cloud and surface flux processes in the tropical eastern Pacific Ocean based on a series of ship-based cloud and flux measurements made during fall (1999–2002) and spring (2000–02) maintenance cruises along the 95° and 110°W Tropical Atmosphere Ocean (TAO) buoy lines between 8°S and 12°N. The year-to-year and seasonal variabilities of many of the meteorological and oceanic means are relatively small. However, notable seasonal variability is found in the northern branch of the intertropical convergence zone, the north–south sea surface temperature gradient, and heat fluxes north of the equator. In the fall, the strengthening of the north–south SST contrast enhances convective activity (more and deeper clouds, precipitation, southerly inflow) in the area around 6°N, 95°W; diurnal variations of low cloud fraction were weak. Spring cloud fraction varied significantly over the diurnal cycle with substantially lower cloud fraction during the day south of 5°N. Relatively low average cloud-base heights around the equator are due to chilling of the marine boundary layer over the cold tongue. Cloud radiative forcing strongly correlates with cloud fraction; clouds in the observation region cool the surface by about 40 W m−2 in both seasons. Cloud forcing estimates from the ship data, the TAO buoys, and International Satellite Cloud Climatology Project (ISCCP) products were combined to form a consensus observation dataset that is compared with the second NCEP reanalysis (NCEP-2) and 40-yr ECMWF Re-Analysis (ERA-40) cloud forcing values. The reanalysis products were within 10 W m−2 of the observations for IR cloud forcing but substantially overestimated the solar cloud forcing, particularly in spring.

scholarly journals Shallow-Water Foraminifera and Other Microscopic Biota of Clipperton Island, Tropical Eastern Pacific

2019 ◽  
Author(s):  
Mary L McGann ◽  
Robert W. Schmieder ◽  
Louis-Philippe Loncke
Keyword(s):  
Shallow Water ◽  
Geographic Location ◽  
Oceanic Islands ◽  
Tropical Pacific ◽  
Eastern Pacific ◽  
North Equatorial Current ◽  
Tropical Eastern Pacific ◽  
Foraminiferal Assemblage ◽  
Island Endemic ◽  
The North

<p></p><p>The recent foraminiferal fauna and associated microbiota of Clipperton Island (10.2833°N, 109.2167°W) were investigated at 20 sites collected in the intertidal zone around the perimeter of the island and from the edge of the inner brackish-water lagoon. Due to the island’s geographic location in a low productivity zone, a lack of variable habitats on and surrounding the island, and heavy surf that pounds the exposed land, a depauperate fauna was recovered although mixed biogeographic affinities are represented. The shallow-water foraminiferal assemblage has no endemics but primarily tropical Indo-Pacific and eastern Pacific (Panamic) affinities, as well as one species of Caribbean affinity. The most abundant taxa are <i>Sorites</i> spp. and <i>Quinqueloculina</i> spp. Noticeably absent are any species of <i>Amphistegina, </i>despite the fact that they are considered ubiquitous in the tropical Pacific. The molluscan fauna has Clipperton Island endemics, a tropical Pacific/Inter-Island endemic, and tropical eastern Pacific oceanic islands/Panamic Molluscan affinities. The ostracods included endemics found restricted to Clipperton Island lagoon, as well as Indo-Pacific and Panamic Province species. The foraminifera, mollusks, and ostracods are thought to disperse to Clipperton Island by way of the North Equatorial Countercurrent and North Equatorial Current, suggesting that the island is indeed a stepping stone for migration both east and west across the Eastern Pacific Barrier.</p><br><p></p>

scholarly journals Reduced Wet-Season Length Detected by Satellite Retrievals of Cloudiness over Brazilian Amazonia: A New Methodology

2018 ◽  
Vol 31 (24) ◽  
pp. 9941-9964 ◽  
Author(s):  
Elisa T. Sena ◽  
M. A. F. Silva Dias ◽  
L. M. V. Carvalho ◽  
P. L. Silva Dias
Keyword(s):  
Rainy Season ◽  
Cloud Cover ◽  
Amazon Basin ◽  
Warm Pool ◽  
Cloud Fraction ◽  
Heat Fluxes ◽  
Significant Shift ◽  
Season Length ◽  
Wet Season ◽  
The North

This study investigates the variability of the seasonal cycle of convection in the Brazilian Amazon basin during the last decades, and examines physical mechanisms that potentially trigger these modifications. A new methodology to evaluate the onset and length of the rainy season using long-term cloud fraction observations from geostationary satellites is proposed and the connection between cloud cycle variability, surface properties, and thermodynamic and dynamic conditions is explored. The results show that cloud cover has significantly decreased over the last decades. The decline in cloudiness is steeper at 1200 UTC (0800 LT), when a trend of up to −6% decade−1 is observed over the central and eastern Amazon. High-cloud-cover reduction is the major contributor to the observed decline in total cloud fraction. Delayed onsets and a reduction of up to 4 days yr−1 in the northern and central Amazon wet-season length are observed. Correlation analyses indicate that the El Niño phenomenon affects the interannual variability of cloudiness in the Amazon, leading to delayed onset and early demise of the rainy season. The tropical South Atlantic, the Pacific warm pool, and the North Atlantic tripole also play a small, but significant, role in the Amazon’s cloudiness variability. The decrease in cloudiness over the Amazon basin reduces the amount of solar radiation reflected back to space while increasing irradiance at the surface. This local warming alters surface heat fluxes and the atmospheric thermodynamic profile, further affecting cloud development. The strong tendencies reported here indicate a significant shift in the Amazonian hydroclimate during the last few decades.

scholarly journals Coastal Clouds at the Eastern Margin of the Southeast Pacific: Climatology and Trends

2016 ◽  
Vol 29 (12) ◽  
pp. 4525-4542 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
Juan Quintana ◽  
Mark J. Falvey ◽  
José A. Rutllant ◽  
René Garreaud
Keyword(s):  
Cloud Cover ◽  
Marine Boundary Layer ◽  
Onset Time ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Physical Factors ◽  
Near Surface ◽  
Low Level ◽  
Drying Trend ◽  
Long Term Trends

Abstract The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent with the subtropical location, cloud types are dominated by stratocumuli having greatest coverage (&gt;7 oktas) and smaller heights (600–750 m) during the nighttime of austral winter and spring. Meridionally, nighttime cloud fraction and cloud-base heights increase from south to north. Long-term trends in mean cloud cover are observed at all sites albeit with a seasonal modulation, with increasing (decreasing) coverage in the spring (fall). Consistent trend patterns are also observed in independent sunshine hour measurements at the same sites. Cloud heights show negative trends of about 100 m decade−1 (1995–2010), although the onset time of this tendency differs between sites. The positive cloud fraction trends during the cloudy season reported here disagree with previous studies, with discrepancies attributed to differences in datasets used or to methodological differences in data analysis. The cloud-base height tendency, together with a less rapid lowering of the subsidence inversion base height, suggests a deepening of the coastal cloud layer. While consistent with the tendency toward greater low-level cloud cover and the known cooling of the marine boundary layer in this region, these tendencies are at odds with a drying trend of the near-surface air documented here as well. Assessing whether this intriguing result is caused by physical factors or by limitations of the data demands more detailed observations, some of which are currently under way.

Simulation of Seasonal Variation of Marine Boundary Layer Clouds over the Eastern Pacific with a Regional Climate Model*

2011 ◽  
Vol 24 (13) ◽  
pp. 3190-3210 ◽  
Author(s):  
Lei Wang ◽  
Yuqing Wang ◽  
Axel Lauer ◽  
Shang-Ping Xie
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Seasonal Cycle ◽  
Marine Boundary Layer ◽  
Eastern Pacific ◽  
Cloud Base ◽  
Low Level ◽  
Surface Latent Heat Flux ◽  
Cloud Regime ◽  
Low Cloud

Abstract The seasonal cycle of marine boundary layer (MBL) clouds over the eastern Pacific Ocean is studied with the International Pacific Research Center (IPRC) Regional Atmospheric Model (iRAM). The results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution, cloud regime transition, and vertical structure of MBL clouds over the eastern Pacific. Although the modeled MBL cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations, the model simulated well the westward deepening and decoupling of the MBL, the rise in cloud base and cloud top of the low cloud decks off the Peru and California coasts, and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast Pacific. In particular, the model reproduced major features of the seasonal variations in stratocumulus decks off the Peru and California coasts, including cloud amount, surface latent heat flux, subcloud-layer mixing, and the degree of MBL decoupling. In both observations and the model simulation, in the season with small low-level cloudiness, surface latent heat flux is large and the cloud base is high. This coincides with weak subcloud-layer mixing and strong entrainment at cloud top, characterized by a high degree of MBL decoupling, while the opposite is true for the season with large low-level cloudiness. This seasonal cycle in low-cloud properties resembles the downstream stratocumulus-to-cumulus transition of marine low clouds and can be explained by the “deepening–decoupling” mechanism proposed in previous studies. It is found that the seasonal variations of low-level clouds off the Peru coast are mainly caused by a large seasonal variability in sea surface temperature, whereas those off the California coast are largely attributed to the seasonal cycle in lower-tropospheric temperature.

scholarly journals On the parameterization of turbulent fluxes over the tropical Eastern Pacific

2006 ◽  
Vol 6 (3) ◽  
pp. 5251-5268
Author(s):  
G. B. Raga ◽  
S. Abarca
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
High Wind ◽  
Tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.

scholarly journals Statistical Analyses of Satellite Cloud Object Data from CERES. Part V: Relationships between Physical Properties of Marine Boundary Layer Clouds

2008 ◽  
Vol 21 (24) ◽  
pp. 6668-6688 ◽  
Author(s):  
Zachary A. Eitzen ◽  
Kuan-Man Xu ◽  
Takmeng Wong
Keyword(s):  
Boundary Layer ◽  
Cluster Analysis ◽  
Physical Properties ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Radiant Energy ◽  
Cloud Fraction ◽  
Cloud Radiative Forcing ◽  
Boundary Layer Clouds ◽  
Shallow Cumulus

Abstract Relationships between physical properties are studied for three types of marine boundary layer cloud objects identified with the Clouds and the Earth’s Radiant Energy System (CERES) footprint data from the Tropical Rainfall Measuring Mission satellite between 30°S and 30°N. Each cloud object is a contiguous region of CERES footprints that have cloud-top heights below 3 km, and cloud fractions of 99%–100% (overcast type), 40%–99% (stratocumulus type), or 10%–40% (shallow cumulus type). These cloud fractions represent the fraction of ∼2 km × 2 km Visible/Infrared Scanner pixels that are cloudy within each ∼10 km × 10 km footprint. The cloud objects have effective diameters that are greater than 300 km for the overcast and stratocumulus types, and greater than 150 km for the shallow cumulus type. The Spearman rank correlation coefficient is calculated between many microphysical/optical [effective radius (re), cloud optical depth (τ), albedo, liquid water path, and shortwave cloud radiative forcing (SW CRF)] and macrophysical [outgoing longwave radiation (OLR), cloud fraction, cloud-top temperature, longwave cloud radiative forcing (LW CRF), and sea surface temperature (SST)] properties for each of the three cloud object types. When both physical properties are of the same category (microphysical/optical or macrophysical), the magnitude of the correlation tends to be higher than when they are from different categories. The magnitudes of the correlations also change with cloud object type, with the correlations for overcast and stratocumulus cloud objects tending to be higher than those for shallow cumulus cloud objects. Three pairs of physical properties are studied in detail, using a k-means cluster analysis: re and τ, OLR and SST, and LW CRF and SW CRF. The cluster analysis of re and τ reveals that for each of the cloud types, there is a cluster of cloud objects with negative slopes, a cluster with slopes near zero, and two clusters with positive slopes. The joint OLR and SST probability plots show that the OLR tends to decrease with SST in regions with boundary layer clouds for SSTs above approximately 298 K. When the cloud objects are split into “dry” and “moist” clusters based on the amount of precipitable water above 700 hPa, the associated OLRs increase with SST throughout the SST range for the dry clusters, but the OLRs are roughly constant with SST for the moist cluster. An analysis of the joint PDFs of LW CRF and SW CRF reveals that while the magnitudes of both LW and SW CRFs generally increase with cloud fraction, there is a cluster of overcast cloud objects that has low values of LW and SW CRF. These objects are generally located near the Sahara Desert, and may be contaminated with dust. Many of these overcast objects also appear in the re and τ cluster with negative slopes.

What Maintains the SST Front North of the Eastern Pacific Equatorial Cold Tongue?*

2007 ◽  
Vol 20 (11) ◽  
pp. 2500-2514 ◽  
Author(s):  
Simon P. de Szoeke ◽  
Shang-Ping Xie ◽  
Toru Miyama ◽  
Kelvin J. Richards ◽  
R. Justin O. Small
Keyword(s):  
Mixed Layer ◽  
Radiative Forcing ◽  
Cold Water ◽  
Eastern Pacific ◽  
Boreal Summer ◽  
Cold Tongue ◽  
Surface Cooling ◽  
Sst Front ◽  
The North ◽  
Atmospheric Feedback

Abstract A coupled ocean–atmosphere regional model suggests a mechanism for formation of a sharp sea surface temperature (SST) front north of the equator in the eastern Pacific Ocean in boreal summer and fall. Meridional convergence of Ekman transport at 5°N is forced by eastward turning of the southeasterly cross-equatorial wind, but the SST front forms considerably south of the maximum Ekman convergence. Geostrophic equatorward flow at 3°N in the lower half of the isothermally mixed layer enhances mixed layer convergence. Cold water is upwelled on or south of the equator and is advected poleward by mean mixed layer flow and by eddies. The mixed layer current convergence in the north confines the cold advection, so the SST front stays close to the equator. Warm advection from the north and cold advection from the south strengthen the front. In the Southern Hemisphere, a continuous southwestward current advects cold water far from the upwelling core. The cold tongue is warmed by the net surface flux, which is dominated by solar radiation. Evaporation and net surface cooling are at a maximum just north of the SST front where relatively cool dry air is advected northward over warm SST. The surface heat flux is decomposed into a response to SST alone, and an atmospheric feedback. The atmospheric feedback enhances cooling on the north side of the front by 178 W m−2, about half of which is due to enhanced evaporation from cold dry advection, while the other half is due to cloud radiative forcing.

scholarly journals On the parameterization of turbulent fluxes over the tropical Eastern Pacific

2007 ◽  
Vol 7 (3) ◽  
pp. 635-643 ◽  
Author(s):  
G. B. Raga ◽  
S. Abarca
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
High Wind ◽  
Tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.

Characterization and Evolution of Marine Heat Waves in the Peruvian Upwelling System

2020 ◽  
Author(s):  
Alice Pietri ◽  
François Colas ◽  
Rodrigo Mogollon ◽  
Dante Espinoza-Morriberón ◽  
Adolfo Chamorro ◽  
...  
Keyword(s):  
Extreme Events ◽  
Coastal Upwelling ◽  
Heat Waves ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
The South ◽  
Tropical Eastern Pacific ◽  
High Pressure Cell ◽  
Upwelling System ◽  
Equatorial Wave

&lt;p align=&quot;justify&quot;&gt;Rapidly developing extreme events such as anomalously warm water events, known as Marine Heat Waves (MHWs), have received considerable attention in the past few years due to the significant impact they have on regional ecosystems and socioeconomic activity. The Peruvian Coastal Upwelling System (PCUS), one of the most productive ecosystem in the world in terms of fisheries, is highly exposed to climate variability in particular because of its geographic location close to the equator, and the influence of the subtropical high pressure cell variability.&lt;/p&gt;&lt;p align=&quot;justify&quot;&gt;The PCUS is highly influenced by El Ni&amp;#241;o events, which have been intensively studied, and whose variability is related to the longest and most intense MHWs in the region. However the very visible El Ni&amp;#241;o events probably overshadowed the MHWs of shorter duration that also have an important impact on the coastal environment as they can often go with other extreme events such as nearshore hypoxia. To date, a census of MHWs of shorter duration (less than 30 days) is lacking in the region.&lt;/p&gt;&lt;p&gt;&lt;span&gt;Here, we investigate the characteristics (spatial variability, frequency, intensity and duration) and evolution of such MHWs in the South Tropical Eastern Pacific, with a focus on the PCUS coastal area where the ecological vulnerability is higher. Several sea surface temperature satellite products are compared to test the sensitivity of the results. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The distinction between El Ni&amp;#241;o events and regular MHWs has a major impact on the statistical distribution of MHWs properties in the South Equatorial and South Tropical Eastern Pacific as well as on their evolution over the last 35 years. First results indicate that in the equatorial region and along the Peruvian coast, fewer MHWs and of shorter duration are observed north than south of 15&amp;#176;S. The observed trend is an increase of MHWs occurrences, duration and intensity in the South Tropical Eastern Pacific over the last 35 years, with the exception of the coastal region off Peru where &lt;/span&gt;&lt;span&gt;t&lt;/span&gt;&lt;span&gt;he trend in occurrences and duration is the same &lt;/span&gt;&lt;span&gt;but &lt;/span&gt;&lt;span&gt;the average temperature anomaly associated to MHWs has decreased. It also seems that there is no apparent preferential season for the occurrence of MHWs. A study of the possible drivers is performed in an attempt to disentangle the role of the local (wind stress, heat fluxes) and remote (equatorial wave activity) forcing. &lt;/span&gt;&lt;/p&gt;

scholarly journals Temporal–Spatial Distribution of Thin Moist Layers in the Midtroposphere over the Tropical Eastern Pacific

2009 ◽  
Vol 22 (19) ◽  
pp. 5102-5114
Author(s):  
Shigenori Otsuka ◽  
Shigeo Yoden
Keyword(s):  
Spatial Distribution ◽  
Annual Variation ◽  
Intertropical Convergence Zone ◽  
Eastern Pacific ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Tropical Eastern Pacific ◽  
Local Maxima ◽  
The North ◽  
The Vertical Distribution

Abstract The temporal–spatial distribution of thin moist layers in the midtroposphere over the tropical eastern Pacific is studied by data analyses of radiosonde soundings and downscaling numerical experiments with a regional model. Radiosonde soundings at San Cristóbal, Galápagos, show frequent existence of thin moist layers between 2 and 10 km in altitude, with a local minimum at 7–8 km. The downscaling experiments with global objective analyses are completed for 2005–06, September and December of 1999–2004, and March of 2000–04. The vertical distribution of thin moist layers has three local maxima at 5, 10, and 16 km, where bimodality of the frequency distribution of water vapor is evident. Between 4 and 7 km, an annual variation is dominant in the occurrence ratio of thin moist layers, which tend to appear in nonconvective regions. In boreal winter, the layers appear to the north of the intertropical convergence zone (ITCZ), whereas in boreal summer the layers appear in the equator-side of the ITCZ. Interannual variations of the appearance of thin moist layers are also studied in 1999–2006, based on the experiments for particular months (March, September, and December). The occurrence ratio is generally high in December and March and low in September. In La Niña years, the annual variation is smaller than that in El Niño years; the occurrence ratio is higher in boreal summer to the south of the ITCZ.

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