Atmospheric stratification over Namibia and the southeast Atlantic Ocean

Abstract. We currently have a limited understanding of the spatial and temporal variability in vertically stratified atmospheric layers over Namibia and the southeast Atlantic (SEA) Ocean. Stratified layers are relevant to the transport and dilution of local and long-range transported atmospheric constituents. This study used eleven years of global positioning system radio occultation (GPS-RO) signal refractivity data (2007–2017) over Namibia and the adjacent ocean surfaces, and three years of radiosonde data from Walvis Bay, Namibia, to study the character and variability in stratified layers. From the GPS-RO data and up to a height of 10 km, we studied the spatial and temporal variability in the point of minimum gradient in refractivity, and the temperature inversion height, depth and strength. We also present the temporal variability of temperature inversions and the boundary layer height (BLH) from radiosondes. The BLH was estimated by the parcel method, the top of a surface-based inversion, the top of a stable layer identified by the bulk Richardson number (RN), and the point of minimum gradient in the refractivity (for comparison with GPS-RO data). A comparison between co-located GPS-RO to radiosonde temperature profiles found good agreement between the two, and an average underestimation of GPS-RO to radiosonde temperatures of −0.45 ± 1.25 °C, with smaller differences further from the surface and with decreasing atmospheric moisture content. The minimum gradient (MG) of refractivity, calculated from these two datasets were generally in good agreement (230 ± 180 m), with an exeption of a few cases when differences exceeded 1000 m. The surface of MG across the region of interest was largely affected by macroscale circulation and changes in atmospheric moisture and cloud, and was not consistent with BLH(RN). We found correlations in the character of low-level inversions with macroscale circulation, radiation interactions with the surface, cloud cover over the ocean and the seasonal maximum in biomass burning over southern Africa. Radiative cooling on diurnal scales also affected elevated inversions between 2.5 and 10 km, with more co-occurring inversions observed at night and in the morning. Elevated inversions formed most frequently over the subcontinent and under subsidence by high-pressure systems in the colder months. Despite this macroscale influence peaking in the winter, the springtime inversions, like those at low levels, were strongest.

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Antarctic Low-Tropospheric Humidity Inversions: 10-Yr Climatology

Journal of Climate ◽

10.1175/jcli-d-12-00446.1 ◽

2013 ◽

Vol 26 (14) ◽

pp. 5205-5219 ◽

Cited By ~ 21

Author(s):

Tiina Nygård ◽

Teresa Valkonen ◽

Timo Vihma

Keyword(s):

Water Vapor ◽

Climate Models ◽

Weather Prediction ◽

Temperature Inversion ◽

Statistical Characteristics ◽

The Arctic ◽

Radiosonde Data ◽

Atmospheric Moisture Budget ◽

Temperature Inversions ◽

The Antarctic

Abstract Humidity inversions are nearly permanently present in the coastal Antarctic atmosphere. This is shown based on an investigation of statistical characteristics of humidity inversions at 11 Antarctic coastal stations using radiosonde data from the Integrated Global Radiosonde Archive (IGRA) from 2000 to 2009. The humidity inversion occurrence was highest in winter and spring, and high atmospheric pressure and cloud-free conditions generally increased the occurrence. A typical humidity inversion was less than 200 m deep and 0.2 g kg−1 strong, and a typical humidity profile contained several separate inversion layers. The inversion base height had notable seasonal variations, but generally the humidity inversions were located at higher altitudes than temperature inversions. Roughly half of the humidity inversions were associated with temperature inversions, especially near the surface, and humidity and temperature inversion strengths as well as depths correlated at several stations. On the other hand, approximately 60% of the humidity inversions were accompanied by horizontal advection of water vapor increasing with height, which is also a probable factor supporting humidity inversions. The spatial variability of humidity inversions was linked to the topography and the water vapor content of the air. Compared to previous results for the Arctic, the most striking differences in humidity inversions in the Antarctic were a much higher frequency of occurrence in summer, at least under clear skies, and a reverse seasonal cycle of the inversion height. The results can be used as a baseline for validation of weather prediction and climate models and for studies addressing changes in atmospheric moisture budget in the Antarctic.

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Modes of Vertical Thermodynamic and Wind Variability over the Maritime Continent

10.5194/acp-2016-843 ◽

2016 ◽

Author(s):

Jennie Bukowski ◽

Derek J. Posselt ◽

Jeffrey S. Reid ◽

Samuel A. Atwood

Keyword(s):

Temporal Variability ◽

Large Scale ◽

Principal Component ◽

Structure Functions ◽

Dimensional Subspace ◽

Radiosonde Data ◽

Spatial And Temporal Variability ◽

Convective Systems ◽

Wind Variability ◽

Wind Profiles

Abstract. The Maritime Content (MC) is an exceedingly complex region, both from the perspective of its meteorology and its aerosol characteristics. Convection in the MC is ubiquitous, and assumes a wide variety of forms under the influence of an evolving large scale dynamic and thermodynamic context. Understanding the interaction between convective systems and their environment, both individually and in the aggregate, requires knowledge of the dominant patterns of spatial and temporal variability. To this end, radiosonde observations from 2008–2016 are examined from three sounding release sites within the MC for the purpose of exploring the dominant vertical temperature, humidity, and wind structures in the region. Principal Component Analysis is applied to the vertical atmospheric column to transform patterns present in radiosonde data into canonical thermodynamic and wind profiles for the MC. Both rotated and non-rotated principal components are considered, and the emerging structure functions reflect the fundamental vertical modes of short-term tropical variability. The results indicate that while there is tremendous spatial and temporal variability across the MC, the primary modes of vertical thermodynamic and wind variability in the region can be represented in a lower-dimensional subspace. In addition, the vertical structures are very similar among different sites around the region, though different structures may manifest more strongly at one location than another. The results indicate that, while very different meteorology may be found in various parts of the MC at any given time, the processes themselves are remarkably consistent. The ability to represent this variability using a limited number of structure functions facilitates analysis of co-variability between atmospheric structure and convective systems, and also enables future systematic model-based ensemble analysis of cloud development, convection, and precipitation over the MC.

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Characteristics of Satellite-Derived Clear-Sky Atmospheric Temperature Inversion Strength in the Arctic, 1980–96

Journal of Climate ◽

10.1175/jcli3915.1 ◽

2006 ◽

Vol 19 (19) ◽

pp. 4902-4913 ◽

Cited By ~ 35

Author(s):

Yinghui Liu ◽

Jeffrey R. Key ◽

Axel Schweiger ◽

Jennifer Francis

Keyword(s):

Temperature Inversion ◽

Atmospheric Temperature ◽

Cold Season ◽

The Arctic ◽

Radiosonde Data ◽

Clear Sky ◽

Dominant Feature ◽

Inversion Strength ◽

Arctic Atmosphere ◽

Temperature Inversions

Abstract The low-level atmospheric temperature inversion is a dominant feature of the Arctic atmosphere throughout most of the year. Meteorological stations that provide radiosonde data are sparsely distributed across the Arctic, and therefore provide little information on the spatial distribution of temperature inversions. Satellite-borne sensors provide an opportunity to fill the observational gap. In this study, a 17-yr time series, 1980–96, of clear-sky temperature inversion strength during the cold season is derived from High Resolution Infrared Radiation Sounder (HIRS) data using a two-channel statistical method. The satellite-derived clear-sky inversion strength monthly mean and trends agree well with radiosonde data. Both increasing and decreasing trends are found in the cold season for different areas. It is shown that there is a strong coupling between changes in surface temperature and changes in inversion strength, but that trends in some areas may be a result of advection aloft rather than warming or cooling at the surface.

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Evaluación de dos modelos para la estimación de la evapotranspiración de referencia con datos CERES

Revista de Teledetección ◽

10.4995/raet.2018.9259 ◽

2018 ◽

pp. 87 ◽

Cited By ~ 4

Author(s):

F. Carmona ◽

M. Holzman ◽

R. Rivas ◽

M.F. Degano ◽

E. Kruse ◽

...

Keyword(s):

Temporal Variability ◽

Reference Evapotranspiration ◽

Important Variable ◽

Spatial And Temporal Variability ◽

Suitable Alternative ◽

Pampean Region ◽

Daily Scale ◽

Weather Stations ◽

Good Agreement

Evapotranspiration is the most important variable in the Pampas plain. Information provided by sensors onboard satellite missions allows represent the spatial and temporal variability of evapotranspiration, which cannot be achieved using only measurements of weather stations. In this work, the Priestley and Taylor (PT) and FAO Penman Monteith (FAO PM) equations were adapted to estimate the reference evapotranspiration, ET0 , using only CERES satellite products (SYN1 and CldTypHist). In order to evaluate the reference evapotranspiration from CERES, a comparison with in situ measurements was conducted. We used ET data provided by the Oficina de Riesgo Agropecuario, corresponding to 24 stations placed in the Pampean Region of Argentina (2001-2016). Results showed very good agreement between the estimates with CERES products and in situ values, with errors between ±0.8 and ±1.1 mm d–1 and r2 greater than 0.75 at daily scale, and errors between ±14 and ±19 mm month–1 and r2 greater than 0.9, at monthly scale better results were obtained with adapted model FAO PM than PT. Finally, ET0 monthly maps for the Pampean Region of Argentina were elaborated, which allowed knowing the temporal-spatial variation in the validation area. In conclusion, the methods presented here are a suitable alternative to estimate the reference evapotranspiration without requiring ground measurements.

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Modes of vertical thermodynamic and wind variability over the Maritime Continent

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-4611-2017 ◽

2017 ◽

Vol 17 (7) ◽

pp. 4611-4626 ◽

Cited By ~ 3

Author(s):

Jennie Bukowski ◽

Derek J. Posselt ◽

Jeffrey S. Reid ◽

Samuel A. Atwood

Keyword(s):

Temporal Variability ◽

Large Scale ◽

Cloud Model ◽

Principal Component ◽

Structure Functions ◽

Radiosonde Data ◽

Spatial And Temporal Variability ◽

Maritime Continent ◽

Convective Systems ◽

Wind Variability

Abstract. The Maritime Continent (MC) is an exceedingly complex region from the perspective of both its meteorology and its aerosol characteristics. Convection in the MC is ubiquitous and assumes a wide variety of forms under the influence of an evolving large-scale dynamic and thermodynamic context. Understanding the interaction between convective systems and their environment, both individually and in the aggregate, requires knowledge of the dominant patterns of spatial and temporal variability. Ongoing cloud model ensemble studies require realistic perturbations to the atmospheric thermodynamic state to devise system sensitivities. Apart from modeling studies, evanescent signals in the tropical system are obscured by the underlying broad-scale meteorological variability, which if constrained could illuminate fine-scale physical processes. To this end, radiosonde observations from 2008 to 2016 are examined from three upper-air sounding sites within the MC for the purpose of exploring the dominant vertical temperature, humidity, and wind structures in the region. Principal component analysis is applied to the vertical atmospheric column to transform patterns present in radiosonde data into canonical thermodynamic and wind profiles for the MC. Both rotated and non-rotated principal components are considered, and the emerging structure functions reflect the fundamental vertical modes of short-term tropical variability. The results indicate that while there is tremendous spatial and temporal variability across the MC, the primary modes of vertical thermodynamic and wind variability in the region can be represented in a lower-dimensional subspace. In addition, the vertical structures are very similar among different sites around the region, though different structures may manifest more strongly at one location than another. The results indicate that, while different meteorology may be found in various parts of the MC at any given time, the processes themselves are remarkably consistent. The ability to represent this variability using a limited number of structure functions facilitates analysis of covariability between atmospheric structure and convective systems and also enables future systematic model-based ensemble analysis of cloud development, convection, and precipitation over the MC.

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