Climatological Patterns Research Articles

Offshore wind climate analysis and variability in the Mediterranean Sea

ABSTRACTThe long‐term offshore wind characteristics in the Mediterranean Sea are assessed using the ERA‐Interim dataset for the period 1979–2014. Three main aspects of the wind climate analysis are examined in detail; the spatio‐temporal behaviour (including variability characteristics) of wind speed and direction for the annual and monthly time scale; the joint association of wind speed and direction for the annual and monthly time scale, and; the wind speed trends and wind direction changes. From this analysis, the systematic wind flow patterns are identified and the general features of the wind climatology patterns are revealed. The most typical examples of stable and intense regional winds are the Mistral (throughout the year) in the Gulf of Lion and the Etesians (during summer) in the Aegean Sea. High values of mean annual variability of wind speed occur over the western part of the basin (Balearic, Tyrrhenian and Ligurian sub‐basins) as well as over the Adriatic and N Aegean Seas, and the E Levantine Basin. Moreover, the assessment of the joint association of wind speed and direction indicates that areas with high values of linear–circular correlation are the ones characterized by intense wind climate. As regards, long‐term changes of wind speed and direction, the linear trend for the former and the angular distance for the latter variable are provided. The fastest increasing wind speed trends are observed in the Ionian, the N Tyrrhenian and N Adriatic Seas, the eastern part of the Algerian Basin up to Balearic Isl. and the western part of the S Levantine Basin while the fastest decreasing ones are observed offshore Monaco, the central Aegean and the E Alboran Seas and the N Levantine Basin. The highest values of angular variance and mean angular distances are depicted for the Ligurian, Balearic and Alboran Seas.

Investigating added value of regional climate modeling in North American winter storm track simulations

Extratropical Cyclone (EC) characteristics depend on a combination of large-scale factors and regional processes. However, the latter are considered to be poorly represented in global climate models (GCMs), partly because their resolution is too coarse. This paper describes a framework using possibilities given by regional climate models (RCMs) to gain insight into storm activity during winter over North America (NA). Recent past climate period (1981–2005) is considered to assess EC activity over NA using the NCEP regional reanalysis (NARR) as a reference, along with the European reanalysis ERA-Interim (ERAI) and two CMIP5 GCMs used to drive the Canadian Regional Climate Model—version 5 (CRCM5) and the corresponding regional-scale simulations. While ERAI and GCM simulations show basic agreement with NARR in terms of climatological storm track patterns, detailed bias analyses show that, on the one hand, ERAI presents statistically significant positive biases in terms of EC genesis and therefore occurrence while capturing their intensity fairly well. On the other hand, GCMs present large negative intensity biases in the overall NA domain and particularly over NA eastern coast. In addition, storm occurrence over the northwestern topographic regions is highly overestimated. When the CRCM5 is driven by ERAI, no significant skill deterioration arises and, more importantly, all storm characteristics near areas with marked relief and over regions with large water masses are significantly improved with respect to ERAI. Conversely, in GCM-driven simulations, the added value contributed by CRCM5 is less prominent and systematic, except over western NA areas with high topography and over the Western Atlantic coastlines where the most frequent and intense ECs are located. Despite this significant added-value on seasonal-mean characteristics, a caveat is raised on the RCM ability to handle storm temporal ‘seriality’, as a measure of their temporal variability at a given location. In fact, the driving models induce some significant footprints on the RCM skill to reproduce the intra-seasonal pattern of storm activity.

On the need to consider multiphasic sensitivity of marine organisms to climate change: a case study of the Antarctic acorn barnacle

Aim Species distribution models (SDMs) are routinely employed to evaluate shifts in the geographic distributions of organisms in response to changing climatic conditions. Many marine invertebrates exhibit a biphasic life cycle: benthic adults and planktonic larvae, which inhabit different environments and may react dissimilarly to anticipated changes in climatological patterns. To date, SDMs applied to benthic species have only considered adult life-history stages. Here, we present the first study in which SDMs have been simultaneously developed for both the larval and adult stages of the same organism. Location The Southern Ocean. Methods Occurrence data for the study species, the Antarctic barnacle Bathylasma corolliforme, were sourced from: (1) benthic geo-referenced records from museum collections and online databases; and (2) observations of planktonic larvae identified with genetic and morphological methods. These records were used to construct two independent SDMs (adult-larvae) with Maxent 3.3.3k; their outputs were then projected to environmental conditions forecast for the year 2050 (IPCC scenario A1B). Results The two different SDMs had high predictive capability and identified preferred environmental conditions of each life-history stage. For the projected 2050 climate change scenario, SDMs predicted that the extent of environmentally suitable areas of both life-history stages was reduced, with planktonic larvae experiencing greater reductions and latitudinal displacement of their suitable areas. Main conclusions For multiphasic species, considering only a single life-history stage while studying distribution shifts may lead to erroneous conclusions for the species as a whole, regardless of the predictive capability of models employed. Ignoring the changes in suitable areas for larval stages can lead to underestimation of habitat reduction, distribution shifts, effects on population connectivity and potential for colonization of newly available habitats.

Impact of soil moisture over Palmer Drought Severity Index and its future projections in Brazil

ABSTRACT Soil moisture is a main factor for the study of drought impacts on vegetation. Drought is a regional phenomenon and affects the food security more than any other natural disaster. Currently, the monitoring of different types of drought is based on indexes that standardize in temporal and regional level allowing, thus, comparison of water conditions in different areas. Therefore, in order to assess the impact of soil moisture during periods of drought, drought Palmer Severity Index was estimated for the entire region of the territory. For this were used meteorological data (rainfall and evapotranspiration) and soil (field capacity, permanent wilting point and water storage in the soil). The data field capacity and wilting point were obtained from the physical properties of soil; while the water storage in soil was calculated considering the water balance model. The results of the PSDI were evaluated during the years 2000 to 2015, which correspond to periods with and without occurrence of drought. In order to assess the future drought projections, considering the set of the Coupled Model Intercomparison rainfall data Project Phase 5 (CMIP5). Climate projections precipitation in CMIP5 for the period 2071-2100 was extracted generating entitled forcing scenarios Representative Concentration Pathways - RCPs, and referred to as RCOP 8.5, corresponding to an approximate radiative forcing the end the twenty-first century of 8.5 Wm-2. The results showed that the PDSI is directly associated with climatological patterns of precipitation and soil moisture in any spatial and temporal scale (including future projections). Therefore, it is concluded that the PDSI is an important index to assess soil moisture different water conditions, as well as the association with economic and social information to create risk maps for subsidies to decision makers.

Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32‐year satellite Global Precipitation Climatology Project data, part I: evaluation and climatological patterns

ABSTRACTThe precipitation regime over the Mediterranean basin is investigated for the period 1979–2010 using monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2). The results show that a clear contrast exists between the more rainy northern part of the study region (Southern Europe) and the drier southern area (North Africa, Iberian Peninsula) and between the western sides (rainsides) of the Iberian, Italian and Balkan peninsulas and their eastern sides (rainshadows). The mean annual precipitation averaged over the study area is P = 593 ± 203 mm year−1, but it has a strong spatial variability ranging from 20 mm year−1 (North Africa) to 1500 mm year−1 (Alps). A significant seasonal variability exists, with the early winter and late autumn months (November and December) being the wettest with precipitation amounts larger than 60 mm month−1. The GPCPv2 satellite precipitation data are satisfactorily correlated with rain gauge measurements from 433 stations within the study area (correlation coefficient R = 0.78 for all stations on a yearly basis, with values ranging between 0.72 and 0.82, depending on the season) with a slight overestimation. They also compare well with the higher spatial and temporal resolution Tropical Rainfall Measuring Mission (TRMM) data, which supports the validity of the present study.

On the vertical distribution of the chlorophyll <i>a</i> concentration in the Mediterranean Sea: a basin-scale and seasonal approach

Abstract. The distribution of the chlorophyll a concentration ([Chl a]) in the Mediterranean Sea, mainly obtained from satellite surface observations or from scattered in situ experiments, is updated by analyzing a database of fluorescence profiles converted into [Chl a]. The database, which includes 6790 fluorescence profiles from various origins, was processed with a specific quality control procedure. To ensure homogeneity between the different data sources, 65 % of fluorescence profiles have been intercalibrated on the basis of their concomitant satellite [Chl a] estimation. The climatological pattern of [Chl a] vertical profiles in four key sites of the Mediterranean Sea has been analyzed. Climatological results confirm previous findings over the range of existing [Chl a] values and throughout the principal Mediterranean trophic regimes. They also provide new insights into the seasonal variability in the shape of the vertical [Chl a] profile, inaccessible through remote-sensing observations. An analysis based on the recognition of the general shape of the fluorescence profile was also performed. Although the shape of [Chl a] vertical distribution characterized by a deep chlorophyll maximum (DCM) is ubiquitous during summer, different forms are observed during winter, thus suggesting that factors affecting the vertical distribution of the biomass are complex and highly variable. The [Chl a] spatial distribution in the Mediterranean Sea mimics, on smaller scales, what is observed in the global ocean. As already evidenced by analyzing satellite surface observations, midlatitude- and subtropical-like phytoplankton dynamics coexist in the Mediterranean Sea. Moreover, the Mediterranean DCM variability appears to be characterized by patterns already observed on the global scale.

Global and regional skill of the seasonal predictions by WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble

The World Meteorological Organization (WMO) Lead Centre for Long-Range Forecast Multi-Model Ensemble (WMO LC-LRFMME) has been established to collect and share long-range forecasts from the WMO designated Global Producing Centres (GPC). In this study, the seasonal skill of the deterministic multi-model prediction of GPCs in WMO LC-LRFMME is investigated. The GPC models included in the analysis cover 30 years of common hindcast period from 1981 to 2010 and real-time forecast for the period from DJF2011/2012 to SON2014. The equal-weighted multi-model ensemble (MME) method is used to produce the MME forecast. We show that the GPC models generally capture the observed climatological patterns and seasonal variations in temperature and precipitation. However, some systematic biases/errors in simulation of the climatological mean patterns and zonal mean profiles are also found, most of which are located in mid-latitudes or high latitudes. The temporal correlation coefficients both of 2 m temperature and precipitation in the tropical region (especially over the ocean) exceed 95%, but drop gradually towards high latitudes and are even negative in the polar region for precipitation. The prediction skills of individual models and the MME over 13 regional climate outlook forum (RCOF) regions for four calendar seasons are also assessed. The prediction skills vary with season and region, with the highest skill being demonstrated by the MME forecasts for the regions of the tropical RCOFs. These predictions are strongly affected by the ENSO over Pacific Islands, Southeast Asia and Central America. Additionally, Southeast of South America and North Eurasian regions show relatively low skills for all seasons when compared to other regions.

Assessment of the Summer South Asian High in Eighteen CMIP5 Models

AbstractThe South Asian High (SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models (GCMs) to capture the major characteristics of the SAH, the authors evaluate 18 atmospheric models that participated in the Coupled Model Intercomparison Project Phase 5/Atmospheric Model Intercomparison Project (CMIP5/AMIP). Results show that the multi-model ensemble (MME) mean is able to capture the climatological pattern of the SAH, although its intensity is slightly underestimated. For the interannual variability of the SAH, the MME exhibits good correlation with the reanalysis for the area and intensity index, but poor skill in capturing the east-west oscillation of the SAH. For the interdecadal trend, the MME shows pronounced increasing trends from 1985 to 2008 for the area and intensity indexes, which is consistent with the re-analysis, but fails to capture the westward shift of the SAH center. The individual models s...

Spatio-temporal patterns in water surface temperature from Landsat time series data in the Chesapeake Bay, U.S.A.

Abstract Water temperature is a key factor used to assess biogeochemical cycles and aquatic habitat quality, and is typically monitored using in situ sensors deployed on distributed piers, buoys or mobile platforms. Due to multiple, spatially and temporally varying influences on surface water temperature, (e.g., solar radiation, water depth, tidal stage, turbidity, and industrial activities) multi-temporal remote sensing observations might effectively be used to link these drivers with observations. However, while low- to moderate-resolution sensors provide temporally continuous observations, large pixel sizes have proven problematic in coastal regions where shoreline influences on pixel radiance contaminate the radiation signal leaving the water surface. To alleviate this problem, we used a dense stack of Landsat TM/ETM+ thermal imagery organized by day of year of acquisition, thus producing a climatology of water temperature. We use these data to analyze the spatial patterns of water surface temperature climatology (e.g., average maximum and minimum temperatures) for the past thirty years. We also explore the impact of power plant thermal effluent on water surface temperature climatology of the Chesapeake Bay tributaries. Finally, we divide the Landsat record into 5-year intervals, and calculate the water surface temperature climatology for each period. Trends in water surface temperature over the Landsat record were then compared against air temperature records available from coastal NOAA weather stations. The resulting data exhibit broad scale patterns, such as water surface climatology differences between the main stem of the Bay and its tributaries. The results also include the influence of urbanization and industrialization such as increases in impervious surface area and thermal effluent from power plants. Trends of increasing water surface temperature and air temperature were found for more than 92% of the Bay. While water temperature was always ~ 2–3° cooler than the air temperature, water temperature has been increasing more rapidly than air temperature in some areas, particularly in the main stem of the Bay and in the Potomac estuary. Therefore, there is a detectable impact of global change on the Chesapeake Bay in the form of an increase in water temperature, which can only partially be explained by increasing air temperatures.

Terrestrial Aridity and Its Response to Greenhouse Warming across CMIP5 Climate Models

Abstract The aridity of a terrestrial climate is often quantified using the dimensionless ratio of annual precipitation (P) to annual potential evapotranspiration (PET). In this study, the climatological patterns and greenhouse warming responses of terrestrial P, Penman–Monteith PET, and are compared among 16 modern global climate models. The large-scale climatological values and implied biome types often disagree widely among models, with large systematic differences from observational estimates. In addition, the PET climatologies often differ by several tens of percent when computed using monthly versus 3-hourly inputs. With greenhouse warming, land P does not systematically increase or decrease, except at high latitudes. Therefore, because of moderate, ubiquitous PET increases, decreases (drying) are much more widespread than increases (wetting) in the tropics, subtropics, and midlatitudes in most models, confirming and expanding on earlier findings. The PET increases are also somewhat sensitive to the time resolution of the inputs, although not as systematically as for the PET climatologies. The changes in the balance between P and PET are also quantified using an alternative aridity index, the ratio , which has a one-to-one but nonlinear correspondence with . It is argued that the magnitudes of changes are more uniformly relevant than the magnitudes of changes, which tend to be much higher in wetter regions. The ratio and its changes are also found to be excellent statistical predictors of the land surface evaporative fraction and its changes.

Analysis of Nonstationary Wind Fluctuations Using the Hilbert-Huang Transform

AbstractClimatological patterns in wind fluctuations on time scales of 1–10 h are analyzed at a meteorological mast at the Yangmeishan wind farm, Yunnan Province, China, using a 2-yr time series of 10-min wind speed observations. For analyzing the spectral properties of nonstationary wind fluctuations in mountain terrain, the Hilbert-Huang transform (HHT) is applied to investigate climatological patterns between wind variability and several variables including time of year, time of day, wind direction, and pressure tendency. Compared with that for offshore sites, the wind variability at Yangmeishan wind farm has a more distinct diurnal cycle, but the seasonal discrepancies and the differences according to directions are not distinct, and the synoptic influences on wind variability are weaker. There is enhanced variability in spring and winter compared with summer and autumn. For flow from the main direction sector, the maximum wind variability is observed in spring. And the severe wind fluctuations are mo...

Assessment of Precipitation Characteristics and Synoptic Pattern Associated with Typhoon Affecting the South Korea

The recent unusual climate and extreme weather events have frequently given unexpected disaster and damages, facing difficulties in the management of water resources. In particular, climate change could result in intensified typhoons, and this would be the worst case scenario that can happen. The primary objective of this study is to identify the patterns of typhoon-induced precipitation and the associated synoptic pattern. This study focused on analyzing precipitation patterns over the South Korea using historic records as opposed to a specified season or duration, and further investigates the potential connection with heavy rainfall to synoptic patterns. In this study, we used the best track data provided by the Regional Specialized Meteorological Center of Japan for 40 years from 1973 to 2012. The patterns of the typhoon-induced precipitation were categorized into four groups according to a given typhoon track information, and then the associated synoptic climatology patterns were further investigated. The results demonstrate that the typhoon-induced precipitation patterns could be grouped and potentially simulated according to the identified synoptic patterns. Our future work will focus on developing a short-term forecasting model of typhoon-induced precipitation considering the identified climate patterns as inputs.

Global climate internal variability in a 2000-year control simulation with Community Earth System Model (CESM)

Using the low-resolution (T31, equivalent to 3.75° × 3.75°) version of the Community Earth System Model (CESM) from the National Center for Atmospheric Research (NCAR), a global climate simulation was carried out with fixed external forcing factors (1850 Common Era. (C.E.) conditions) for the past 2000 years. Based on the simulated results, spatio-temporal structures of surface air temperature, precipitation and internal variability, such as the El Nino-Southern Oscillation (ENSO), the Atlantic Multi-decadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO), were compared with reanalysis datasets to evaluate the model performance. The results are as follows: 1) CESM showed a good performance in the long-term simulation and no significant climate drift over the past 2000 years; 2) climatological patterns of global and regional climate changes simulated by the CESM were reasonable compared with the reanalysis datasets; and 3) the CESM simulated internal natural variability of the climate system performs very well. The model not only reproduced the periodicity of ENSO, AMO and PDO events but also the 3–8 years variability of the ENSO. The spatial distribution of the CESM-simulated NAO was also similar to the observed. However, because of weaker total irradiation and greenhouse gas concentration forcing in the simulation than the present, the model performances had some differences from the observations. Generally, the CESM showed a good performance in simulating the global climate and internal natural variability of the climate system. This paves the way for other forced climate simulations for the past 2000 years by using the CESM.

Classification and Synoptic Analysis of Subtropical Cyclones within the Northeastern Atlantic Ocean

AbstractSince more research is needed on subtropical cyclones (STCs) formed within the North Atlantic eastern basin, this survey analyzes them from a synoptic point of view, on a climatological basis, with the main aims of studying their common features, complementing other studies of these storms in the North Atlantic, and aiding the forecasting community. Fifteen cases of STCs were identified during the period 1979–2011 by applying a set of criteria from two databases. Composite analysis reveals that an extratropical depression acts as a precursor when it is isolated from the westerlies and then suffers a deepening when becoming subtropical instead of decaying through occlusion. This process is accompanied by an atmospheric circulation, within the North Atlantic, whose main feature is characterized by notable departures from the climatological pattern with a statistically significant anomalous high pressure to the north of the STCs. Three conceptual models of synoptic pattern of subtropical cyclogenesis are derived and show that these departures appeared because the westerly circulation moves poleward and/or the flow has a great meridional component, with the possibility of a blocked flow pattern occurring. Moreover, the identified STCs predominantly formed in a highly sheared (>10 m s−1) environment with low sea surface temperature values (<25°C), which differs from the dominant features of STCs in the North Atlantic, especially within its western region. Finally, a recent (2010) STC, identified by the authors, is synoptically discussed in order to achieve a better interpretation of the general results.

Connections between the South Asian summer monsoon and the tropical sea surface temperature in CMIP5

The South Asian summer monsoon (SASM) precipitation is analyzed based on reanalysis datasets and historical simulation results from 23 climate models of the Coupled Model Intercomparison Project phase 5 (CMIP5). The results show that most models reproduce well the climatological pattern of SASM precipitation, but the main rainfall period lags that of the reanalysis by one month. The relationship between the simulated SASM precipitation and sea surface temperature anomalies (SSTAs) is quite similar to the reanalysis data. This is attributed to the well-reproduced Walker cell anomaly in the tropical zone. It is projected that the negative correlation between SASM precipitation and SSTAs in the eastern equatorial Pacific will weaken and even reverse to a positive one in the period 2070–2096 under the representative concentration pathway (RCP) scenario with strong external forcing (RCP8.5), while the change of the correlation under moderate forcing (RCP4.5) still has great uncertainty.

An intercomparison of CMIP5 and CMIP3 models for interannual variability of summer precipitation in Pan‐Asian monsoon region

ABSTRACTTwenty‐one climate models from Coupled Model Intercomparison Project Phase 3 (CMIP3) and thirty‐one models from the project's Phase 5 (CMIP5) were used to evaluate model reproducibility in assessing interannual variability of summer precipitation in Pan‐Asian monsoon region. The results show that both the multi‐model ensemble means of the best eight models and of the thirty‐one CMIP5 models are more skilful than those of the CMIP3 models in simulating the climatological pattern and the dominant mode of summer precipitation in Pan‐Asian monsoon region. CMIP5 models show improved skill in representing the main characteristic of the first mode of summer precipitation in Pan‐Asian monsoon region, which is a meridional tripole pattern from north to south occurring east of the 80°E region. That is, owing to the improved El Niño–Southern Oscillation (ENSO) pattern and the relationship between Antarctic oscillation in the southern Pacific Ocean (AAOSP) and ENSO, the first dominant mode of summer precipitation in Pan‐Asian monsoon region are captured by CMIP5 models, which indicates that these models are more skilful in simulating the air–sea interaction of the Southern Hemisphere.

Using a Snow Drift Model to Simulate Eolian Drift and Snowfall on the Summit of Mauna Kea, Hawaii

The goal of this research is to help develop a better understanding of the micro-meteorology of the Mauna Kea summit area and its relationship to the distribution and population health of the Wēkiu bug (Nysius wekiuicola). SnowModel, a spatially distributed snow-evolution model, is used to construct snowfall and summit eolian debris (known as bug fall throughout this study) accumulation maps across the summit. Eight weather stations associated with astronomical observatories on the summit ridges and four Davis weather stations located in various cinder cones (pu‘u in Hawaiian), provide the meteorological observations needed as input to run SnowModel. Snow depth observations taken after a passing cold front in January 2011 are used to help validate the model accumulation predictions prior to the climatological study. Observations from summit weather stations over a three-year period (2008, 2009, and 2010) are used as input for the modeled summit accumulations of snowfall and bug fall presented in this study. For the snowfall maps, only weather data from days during which snow fell are included. For the bug-fall estimates, all days where valid weather data are available are included in the model output. Since there are no comprehensive data available on the distribution of bug fall, the bug-fall maps only provide a climatological pattern, without reference to the magnitude of the bug fall. The greatest modeled snow accumulations are found on Pu‘u Wēkiu and Pu‘u Haukea. Similar results are found in the climatological bug-fall accumulation pattern. Prevailing wind direction is most critical for the distribution of snowfall and bug fall, with maximum accumulations occurring on the lee side of ridges and crests. Favorable Wēkiu bug trapping sites in which bugs were found historically are spatially well collocated with snowfall and bug-fall accumulations, suggesting that the results of this study will be of interest to entomologists in locating Wēkiu bug populations.

FORAGES AND PASTURES SYMPOSIUM: Assessing drought vulnerability of agricultural production systems in context of the 2012 drought1,2

Weather and climate events and agronomic enterprise are coupled via crop phenology and yield, which is temperature and precipitation dependent. Additional coupling between weather and climate and agronomic enterprise occurs through agricultural practices such as tillage, irrigation, erosion, livestock management, and forage. Thus, the relationship between precipitation, temperature, and yield is coupled to the relationship between temperature, precipitation, and drought. Unraveling the different meteorological and climatological patterns by comparing different growing seasons provides insight into how drought conditions develop and what agricultural producers can do to mitigate and adapt to drought conditions. The 2012 drought in the United States greatly impacted the agricultural sector of the economy. With comparable severity and spatial extent of the droughts of the 1930s, 1950s, and 1980s, the 2012 drought impacted much of the U.S. crop and livestock producers via decreased forage and feed. This brief summary of drought impacts to agricultural production systems includes 1) the basics of drought; 2) the meteorology and climatology involved in forecasting, predicting, and monitoring drought with attribution of the 2012 drought explored in detail; and 3) comparative analysis completed between the 2011 and 2012 growing season. This synthesis highlights the complex nature of drought in agriculture production systems as producers prepare for future climate variability.

Climatology of Upper Tropospheric–Lower Stratospheric (UTLS) Jets and Tropopauses in MERRA

Abstract A global climatology (1979–2012) from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) shows distributions and seasonal evolution of upper tropospheric jets and their relationships to the stratospheric subvortex and multiple tropopauses. The overall climatological patterns of upper tropospheric jets confirm those seen in previous studies, indicating accurate representation of jet stream dynamics in MERRA. The analysis shows a Northern Hemisphere (NH) upper tropospheric jet stretching nearly zonally from the mid-Atlantic across Africa and Asia. In winter–spring, this jet splits over the eastern Pacific, merges again over eastern North America, and then shifts poleward over the North Atlantic. The jets associated with tropical circulations are also captured, with upper tropospheric westerlies demarking cyclonic flow downstream from the Australian and Asian monsoon anticyclones and associated easterly jets. Multiple tropopauses associated with the thermal tropopause “break” commonly extend poleward from the subtropical upper tropospheric jet. In Southern Hemisphere (SH) summer, the tropopause break, along with a poleward-stretching secondary tropopause, often occurs across the tropical westerly jet downstream of the Australian monsoon region. SH high-latitude multiple tropopauses, nearly ubiquitous in June–July, are associated with the unique polar winter thermal structure. High-latitude multiple tropopauses in NH fall–winter are, however, sometimes associated with poleward-shifted upper tropospheric jets. The SH subvortex jet extends down near the level of the subtropical jet core in winter and spring. Most SH subvortex jets merge with an upper tropospheric jet between May and December; although much less persistent than in the SH, merged NH subvortex jets are common between November and April.

Oscillation modes of humidity over the Amazon basin derived from GPS RO profiles

The Global Positioning System radio occultation (GPS RO) technique provides vertical profiles of refractivity from which water vapor can be derived. It is possible to reproduce global, synoptic, and regional climatological patterns. From Formosa Satellite 3/Constellation Observing System for Meteorology Ionosphere and Climate mission data (2006–2013), the variability of the moistest region of Southern Hemisphere as the Amazon basin is analyzed. Applying different spatial and temporal filters, oscillation modes of the integrated specific humidity (Q) are found. A slight decreasing trend in Q is found during the studied period. Zonal variability of this variable averaged in time between Amazon basin latitudes presents a main mode of oscillation of a wavelength of one quarter of the Earth (T4). A secondary mode of wavelength at around T6 wavelength is also found after high‐pass filtering the original signal. In turn, temporal variability averaged over Amazon basin latitudes shows a wavelength at around 12 months, while secondary modes of 6 months are found.