Variability of Monthly Diurnal Cycle Composites of TOA Radiative Fluxes in the Tropics

2013 ◽  
Vol 71 (2) ◽  
pp. 754-766 ◽  
Author(s):  
Patrick C. Taylor
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Longwave Radiation ◽  
Atmospheric Variability ◽  
Radiative Fluxes ◽  
System Variability ◽  
Synchronous Orbit ◽  
Cloud Evolution ◽  
The Tropics ◽  
The Impact

Abstract Earth system variability is generated by a number of different sources and time scales. Understanding sources of atmospheric variability is critical to reducing the uncertainty in climate models and to understanding the impacts of sampling on observational datasets. The diurnal cycle is a fundamental variability evident in many geophysical variables—including top-of-the-atmosphere (TOA) radiative fluxes. This study considers aspects of the TOA flux diurnal cycle not previously analyzed: namely, deseasonalized variations in the monthly diurnal cycle composites, termed monthly diurnal cycle variability. Significant variability in the monthly diurnal cycle composites is found in both outgoing longwave radiation (OLR) and reflected shortwave (RSW). OLR and RSW monthly diurnal cycle variability exhibits a regional structure that follows traditional, climatological diurnal cycle categorization by prevailing cloud and surface types. The results attribute monthly TOA flux diurnal cycle variability to variations in the diurnal cloud evolution, which is sensitive to monthly atmospheric dynamic- and thermodynamic-state anomalies. The results also suggest that monthly diurnal cycle variability can amplify or buffer monthly TOA flux anomalies, depending on the region. Considering the impact of monthly diurnal cycle variability on monthly TOA flux anomalies, the results suggest that monthly TOA flux diurnal cycle variability must be considered when constructing a TOA flux dataset from sun-synchronous orbit. The magnitude of monthly diurnal composite variability in OLR and RSW is regionally dependent—1–7 W m−2 and 10%–80% relative to interannual TOA flux variability. The largest (4–7 W m−2; 40%–80%) and smallest (1–3 W m−2; 10%–30%) TOA flux uncertainties occur in convective and nonconvective regions, respectively, over both land and ocean.

scholarly journals An Evaluation of Northern Australian Wet Season Rainfall Bursts in CMIP5 Models

2018 ◽  
Vol 31 (19) ◽  
pp. 7789-7802 ◽  
Author(s):  
Sugata Narsey ◽  
Michael J. Reeder ◽  
Christian Jakob ◽  
Duncan Ackerley
Keyword(s):  
Outgoing Longwave Radiation ◽  
Climate Models ◽  
Longwave Radiation ◽  
Cmip5 Models ◽  
Madden Julian Oscillation ◽  
Wet Season ◽  
The North ◽  
Coupled Climate Models ◽  
The Tropics ◽  
The Relationship

The simulation of northern Australian wet season rainfall bursts by coupled climate models is evaluated. Individual models produce vastly different amounts of precipitation over the north of Australia during the wet season, and this is found to be related to the number of bursts they produce. The seasonal cycle of bursts is found to be poor in most of the models evaluated. It is known that northern Australian wet season bursts are often associated with midlatitude Rossby wave packets and their surface signature as they are refracted toward the tropics. The relationship between midlatitude waves and the initiation of wet season bursts is simulated well by the models evaluated. Another well-documented influence on the initiation of northern Australian wet season bursts is the Madden–Julian oscillation (MJO). No model adequately simulated the tropical outgoing longwave radiation temporal–spatial patterns seen in the reanalysis-derived OLR. This result suggests that the connection between the MJO and the initiation of northern Australian wet season bursts in models is poor.

scholarly journals Model-based Climatology of Diurnal Variability in Stratospheric Ozone as a Data Analysis Tool

2019 ◽  
Author(s):  
Stacey M. Frith ◽  
Pawan K. Bhartia ◽  
Luke D. Oman ◽  
Natalya A. Kramarova ◽  
Richard D. McPeters ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Analysis Tool ◽  
Diurnal Variability ◽  
Data Merging ◽  
Wide Range ◽  
Synchronous Orbit ◽  
Mean Differences ◽  
The Tropics

Abstract. Observational studies of stratospheric ozone often involve data from multiple instruments that measure the ozone at different times of day. There has been an increased awareness of the potential impact of the diurnal cycle when interpreting measurements of stratospheric ozone at altitudes in the mid to upper stratosphere. To address this issue we present a climatological representation of diurnal variations in ozone with a half hour temporal resolution as a function of latitude, pressure and month, based on output from the NASA GEOS-GMI chemistry model run. This climatology can be applied in a wide range of ozone data analyses, including data inter-comparisons, data merging, and analysis of data from a single platform in a non-sun-synchronous orbit. We evaluate the diurnal climatology by comparing mean differences between ozone measurements made at different local solar times to the differences predicted by the diurnal model. The ozone diurnal cycle is a complicated function of latitude, pressure and season, with variations of less than 5 % in the tropics and sub-tropics, increasing to more than 15 % near the polar summer boundary in the upper stratosphere. These results compare well with previous modeling simulations and are supported by similar size variations in satellite observations. We present several example applications of the climatology in currently relevant data studies. We also compare this diurnal climatology to the diurnal signal from a previous iteration of the free-running GEOS Chemistry Climate Model (GEOSCCM) and to the ensemble runs of GEOS-GMI to test the sensitivity of the model diurnal cycle to changes in model formulation and simulated time period.

Quasi-Biweekly Extensions of the Monsoon Winds and the Philippines Diurnal Cycle

2021 ◽  
Author(s):  
Michael B. Natoli ◽  
Eric D. Maloney
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Transition Period ◽  
Intraseasonal Oscillation ◽  
Maximum Amplitude ◽  
Longwave Radiation ◽  
The Philippines ◽  
Boreal Summer ◽  
Monsoon Winds ◽  
The Impact

AbstractThe impact of quasi-biweekly variability in the monsoon southwesterly winds on the precipitation diurnal cycle in the Philippines is examined using CMORPH precipitation, ERA5 reanalysis, and outgoing longwave radiation (OLR) fields. Both a case study during the 2018 Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign and a 23-year composite analysis are used to understand the effect of the QBWO on the diurnal cycle. QBWO events in the west Pacific, identified with an extended EOF index, bring increases in moisture, cloudiness, and westerly winds to the Philippines. Such events are associated with significant variability in daily mean precipitation and the diurnal cycle. It is shown that the modulation of the diurnal cycle by the QBWO is remarkably similar to that by the boreal summer intraseasonal oscillation (BSISO). The diurnal cycle reaches a maximum amplitude on the western side of the Philippines on days with average to above average moisture, sufficient insolation, and weakly offshore prevailing wind. This occurs during the transition period from suppressed to active large-scale convection for both the QBWO and BSISO.Westerly monsoon surges associated with QBWO variability generally exhibit active precipitation over the South China Sea (SCS), but a depressed diurnal cycle. These results highlight that modes of large-scale convective variability in the tropics can have a similar impact on the diurnal cycle if they influence the local scale environmental background state similarly.

UV-Indien Network- a network dedicated to the long-term monitoring of UV radiation in the Indian Ocean.

2020 ◽  
Author(s):  
Thierry Portafaix ◽  
Kevin Lamy ◽  
Jean-Baptiste Forestier ◽  
Solofo Rakotoniaina ◽  
Vincent Amélie
Keyword(s):  
Indian Ocean ◽  
Uv Radiation ◽  
Cloud Cover ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Global Climate Models ◽  
Climate Projections ◽  
Second Phase ◽  
The Tropics ◽  
The Impact

<p>Radiation (UV) is one of the main components of solar radiation transmitted by the Earth's atmosphere. Exposure to UV radiation can have both positive and negative effects on the biosphere and humans in particular. Overexposure significantly increases the risk of skin cancer and eye problems.</p><p>Ozone, cloud cover and zenithal solar angle are the main parameters affecting UV radiation levels at the surface. Stratospheric ozone in particular strongly absorbs UV radiation. A dense cloud cover absorbs UV radiation, while a split cloud cover may tend to amplify it.</p><p>Although the stratospheric ozone layer is showing signs of recovery from reduced ozone-depleting substances. The impact of greenhouse gases on the climate is still in increase and global climate models anticipate an acceleration in Brewer-Dobson Circulation, which would lead to lower ozone levels in the tropics. Butler et al. (2016) estimate a decrease in stratospheric ozone in the tropics of 5 to 10 DU for all climate scenarios. Some recent projections (Lamy et al., 2019) predict a 2-3% increase in UVR in the southern tropical band, a region where UV levels are already extreme.</p><p>The purpose of the UV-Indien network is to :</p><p>- Monitor UV levels at different sites in the Western Indian Ocean (WIO)</p><p>- Describe the annual and inter-annual variability of UV radiation in the WIO</p><p>- Perform regional climate projections of UV radiations, validated by quality ground measurements.</p><p>UV-Indien is split into three phases. The first phase began in 2016, with the deployment of the first measurement sites (Reunion Island, Madagascar, Seychelles, Rodrigues). These sites are equipped with a broadband radiometer measuring the UVI and a camera estimating the coverage and sometimes a spectrometer for the measurement of total ozone. The second phase from 2019, sees the extension of this network to 4 other sites (Juan de Nova, Diego Suarez, Fort Dauphin and Grande Comoros). The data validation phase began in 2019 (comparative study with satellite data) and will also propose the study of the variability of UV radiation on different sites. Finally, climate projections will be made from 2020 onwards and will use data from the network to validate the results.</p><p>The aim of this communication is to describe the entire network and its objectives. The first results, as well as the first climatologies will also be discussed.</p>

scholarly journals Evaluating the Diurnal Cycle of Upper-Tropospheric Ice Clouds in Climate Models Using SMILES Observations

2015 ◽  
Vol 72 (3) ◽  
pp. 1022-1044 ◽  
Author(s):  
Jonathan H. Jiang ◽  
Hui Su ◽  
Chengxing Zhai ◽  
T. Janice Shen ◽  
Tongwen Wu ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Space Station ◽  
Temporal Patterns ◽  
Spatial And Temporal Patterns ◽  
Ice Clouds ◽  
Diurnal Variability ◽  
Diurnal Cycles ◽  
Ice Cloud ◽  
The Tropics

Abstract Upper-tropospheric ice cloud measurements from the Superconducting Submillimeter Limb Emission Sounder (SMILES) on the International Space Station (ISS) are used to study the diurnal cycle of upper-tropospheric ice cloud in the tropics and midlatitudes (40°S–40°N) and to quantitatively evaluate ice cloud diurnal variability simulated by 10 climate models. Over land, the SMILES-observed diurnal cycle has a maximum around 1800 local solar time (LST), while the model-simulated diurnal cycles have phases differing from the observed cycle by −4 to 12 h. Over ocean, the observations show much smaller diurnal cycle amplitudes than over land with a peak at 1200 LST, while the modeled diurnal cycle phases are widely distributed throughout the 24-h period. Most models show smaller diurnal cycle amplitudes over ocean than over land, which is in agreement with the observations. However, there is a large spread of modeled diurnal cycle amplitudes ranging from 20% to more than 300% of the observed over both land and ocean. Empirical orthogonal function (EOF) analysis on the observed and model-simulated variations of ice clouds finds that the first EOF modes over land from both observation and model simulations explain more than 70% of the ice cloud diurnal variations and they have similar spatial and temporal patterns. Over ocean, the first EOF from observation explains 26.4% of the variance, while the first EOF from most models explains more than 70%. The modeled spatial and temporal patterns of the leading EOFs over ocean show large differences from observations, indicating that the physical mechanisms governing the diurnal cycle of oceanic ice clouds are more complicated and not well simulated by the current climate models.

scholarly journals Investigating the impact of cloud-radiative feedbacks on tropical precipitation extremes

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Brian Medeiros ◽  
Amy C. Clement ◽  
James J. Benedict ◽  
Bosong Zhang
Keyword(s):  
Extreme Precipitation ◽  
Climate Models ◽  
Longwave Radiation ◽  
Extreme Rainfall ◽  
Radiative Effects ◽  
Tropical Oceans ◽  
Cloud Radiative Effects ◽  
Radiative Feedbacks ◽  
Mean Climate ◽  
The Impact

AbstractAlthough societally important, extreme precipitation is difficult to represent in climate models. This study shows one robust aspect of extreme precipitation across models: extreme precipitation over tropical oceans is strengthened through a positive feedback with cloud-radiative effects. This connection is shown for a multi-model ensemble with experiments that make clouds transparent to longwave radiation. In all cases, tropical extreme precipitation reduces without cloud-radiative effects. Qualitatively similar results are presented for one model using the cloud-locking method to remove cloud feedbacks. The reduced extreme precipitation without cloud-radiative feedbacks does not arise from changes in the mean climate. Rather, evidence is presented that cloud-radiative feedbacks enhance organization of convection and most extreme precipitation over tropical oceans occurs within organized systems. This result suggests that climate models must correctly predict cloud structure and properties, as well as capture the essence of organized convection in order to accurately represent extreme rainfall.

scholarly journals Systematic Model Error: The Impact of Increased Horizontal Resolution versus Improved Stochastic and Deterministic Parameterizations

2012 ◽  
Vol 25 (14) ◽  
pp. 4946-4962 ◽  
Author(s):  
J. Berner ◽  
T. Jung ◽  
T. N. Palmer
Keyword(s):  
Climate Models ◽  
Zonal Flow ◽  
Model Error ◽  
Horizontal Resolution ◽  
Systematic Bias ◽  
Model Errors ◽  
Tropical Variability ◽  
The Tropics ◽  
Ecmwf Model ◽  
The Impact

Abstract Long-standing systematic model errors in both tropics and extratropics of the ECMWF model run at a horizontal resolution typical for climate models are investigated. Based on the hypothesis that the misrepresentation of unresolved scales contributes to the systematic model error, three model refinements aimed at their representation—fluctuating or deterministically—are investigated. Increasing horizontal resolution to explicitly simulate smaller-scale features, representing subgrid-scale fluctuations by a stochastic parameterization, and improving the deterministic physics parameterizations all lead to a decrease in the systematic bias of the Northern Hemispheric circulation. These refinements reduce the overly zonal flow and improve the model’s ability to capture the frequency of blocking. However, the model refinements differ greatly in their impact in the tropics. While improving the deterministic and introducing stochastic parameterizations reduces the systematic precipitation bias and improves the characteristics of convectively coupled waves and tropical variability in general, increasing horizontal resolution has little impact. The fact that different model refinements can lead to reductions in systematic model error is consistent with the hypothesis that unresolved scales play an important role. At the same time, this degeneracy of the response to different forcings can lead to compensating model errors. Hence, if one takes the view that stochastic parameterization should be an important element of next-generation climate models, if only to provide reliable estimates of model uncertainty, then a fundamental conclusion of this study is that stochasticity should be incorporated within the design of physical process parameterizations and improvements of the dynamical core and not added a posteriori.

scholarly journals Revisiting the Relationship among Metrics of Tropical Expansion

2018 ◽  
Vol 31 (18) ◽  
pp. 7565-7581 ◽  
Author(s):  
D. W. Waugh ◽  
K. M. Grise ◽  
W. J. M. Seviour ◽  
S. M. Davis ◽  
N. Davis ◽  
...  
Keyword(s):  
Climate Models ◽  
Longwave Radiation ◽  
Systematic Investigation ◽  
Hadley Cell ◽  
Subtropical High ◽  
Coupled Climate Models ◽  
Dry Zone ◽  
The Tropics ◽  
The Relationship

There is mounting evidence that the width of the tropics has increased over the last few decades, but there are large differences in reported expansion rates. This is, likely, in part due to the wide variety of metrics that have been used to define the tropical width. Here we perform a systematic investigation into the relationship among nine metrics of the zonal-mean tropical width using preindustrial control and abrupt quadrupling of CO2 simulations from a suite of coupled climate models. It is shown that the latitudes of the edge of the Hadley cell, the midlatitude eddy-driven jet, the edge of the subtropical dry zones, and the Southern Hemisphere subtropical high covary interannually and exhibit similar long-term responses to a quadrupling of CO2. However, metrics based on the outgoing longwave radiation, the position of the subtropical jet, the break in the tropopause, and the Northern Hemisphere subtropical high have very weak covariations with the above metrics and/or respond differently to increases in CO2 and thus are not good indicators of the expansion of the Hadley cell or subtropical dry zone. The differing variability and responses to increases in CO2 among metrics highlights that care is needed when choosing metrics for studies of the width of the tropics and that it is important to make sure the metric used is appropriate for the specific phenomena and impacts being examined.

Propagation and Diurnal Evolution of Warm Season Cloudiness in the Australian and Maritime Continent Region

2008 ◽  
Vol 136 (3) ◽  
pp. 973-994 ◽  
Author(s):  
T. D. Keenan ◽  
R. E. Carbone
Keyword(s):  
Diurnal Cycle ◽  
Warm Season ◽  
The United States ◽  
Daily Basis ◽  
Heat Sources ◽  
Maritime Continent ◽  
Synoptic Conditions ◽  
Subsequent Event ◽  
The Tropics ◽  
The Impact

Abstract Warm season cold cloud-top climatology in the Austral–Indonesian region is examined for evidence of propagating modes of precipitation that originate from elevated heat sources and the diurnal heating cycle. Using satellite-inferred cloudiness from the period 1996–2001 as a proxy for rainfall, this coherent regeneration process and subsequent event propagation is found to consistently occur from the midlatitudes (30°–40°S) to the tropics (10°–20°S) in the Austral region. Given favorable environmental shear at midlatitudes, long-lived eastward-propagating events are observed to occur regularly with a span and duration typically larger than observed by Carbone et al. The genesis of these events, while intermittent, is directly related to elevated heat sources and the diurnal cycle, similar to the United States. However, given the relatively flat terrain of Australia, an elevated heat source is often insufficient, thus increasing the relative influence of transient synoptic forcing. In the tropics, the thermal forcing associated with elevated terrain found over the islands of the Maritime Continent and the land–sea interface is increasingly dominant on daily basis. While eastward- and westward-propagating events are found in the more varied environment of the monsoon regime, evidence for meridionally propagating modes is also found. In this manner, complex interactions occur that modify the location and timing of clouds that develop over neighboring oceanic and continental locations. The impact of convection initially linked to the New Guinea highlands and subsequently impacting the Java Sea region is particularly evident affecting the observed diurnal cycle. The subtropics show characteristics intermediate between the above extremes. With the seasonal cycle, the spring environment favors eastward-propagating events but in summer there is an increasing frequency of diurnally forced quasi-stationary development over elevated terrain enhanced by favorable synoptic conditions. Overall the subtropical summer events have a shorter duration and span than their spring counterparts. The increased environmental steering winds and shear in spring are thought to be the primary reason.

scholarly journals Diagnosing the average spatio-temporal impact of convective systems – Part 2: A model inter-comparison using satellite data

2014 ◽  
Vol 14 (7) ◽  
pp. 9155-9201 ◽  
Author(s):  
M. S. Johnston ◽  
S. Eliasson ◽  
P. Eriksson ◽  
R. M. Forbes ◽  
A. Gettelman ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Rain Rate ◽  
Climate Models ◽  
Deep Convection ◽  
Geographical Location ◽  
Longwave Radiation ◽  
Convective Systems ◽  
Deep Convective Systems ◽  
Spatio Temporal ◽  
Ice Water

Abstract. The representation of the effect of tropical deep convective (DC) systems on upper-tropospheric moist processes and outgoing longwave radiation (OLR) is evaluated in the climate models EC-Earth, ECHAM6, and CAM5 using satellite observations. A composite technique is applied to thousands of deep convective systems that are identified using local rain rate (RR) maxima in order to focus on the temporal evolution of the deep convective processes in the model and observations. The models tend to over-produce rain rates less than about 3 mm h−1 and underpredict the occurrence of more intense rain. While the diurnal distribution of oceanic rain rate maxima in the models is similar to the observations, the land-based maxima are out of phase. Over land, the diurnal cycle of rain is too intense, with DC events occurring at the same position on subsequent days, while the observations vary more in timing and geographical location. Despite having a larger climatological mean upper tropospheric relative humidity, models closely capture the observed moistening of the upper troposphere following the peak rain rate in the deep convective systems. A comparison of the evolution of vertical profiles of ice water content and cloud fraction shows significant differences between models and with the observations. Simulated cloud fractions near the tropopause are also larger than observed, but the corresponding ice water contents are smaller compared to the observations. EC-Earth's CF at pressure levels > 300 hPa are generally less than the obervations while the other models tend to have larger CF for similar altitudes. The models' performance for ocean-based systems seems to capture the evolution of DC systems fairly well, but the land-based systems show significant discrepancies. In particular, the models have a significantly stronger diurnal cycle at the same geo-spatial position. Finally, OLR anomalies associated with deep convection are in reasonable agreement with the observations. This study shows that such agreement with observations can be achieved in different ways in the three models due to different representations of deep convection processes and compensating errors.

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