Browse

You are looking at 1 - 10 of 121,525 items for

  • Refine by Access: All Content x
Clear All
Joaquín E. Blanco
,
Rodrigo Caballero
,
George Datseris
,
Bjorn Stevens
,
Sandrine Bony
,
Or Hadas
, and
Yohai Kaspi

Abstract

The Northern and Southern Hemispheres reflect on average almost equal amounts of sunlight due to compensating hemispheric asymmetries in clear-sky and cloud albedo. Recent work indicates that the cloud albedo asymmetry is largely due to clouds in extratropical oceanic regions. Here, we investigate the proximate causes of this extratropical cloud albedo asymmetry using a cloud-controlling factor (CCF) approach. We develop a simple index that measures the skill of CCFs, either individually or in combination, in predicting the asymmetry. The index captures the contribution to the asymmetry due to interhemispheric differences in the probability distribution function of daily CCF values. Cloud albedo is quantified using daily MODIS satellite retrievals, and is related to range of CCFs derived from the ERA5 reanalysis product. We find that sea-surface temperature is the CCF that individually explains the largest fraction of the asymmetry, followed by surface wind. The asymmetry is predominantly due to low clouds, and our results are consistent with prior local-scale modelling work showing that marine boundary-layer clouds become thicker and more extensive as surface wind increases and surface temperature cools. The asymmetry is consistent with large-scale control of storm track intensity and surface winds by meridional temperature gradients: persistently cold and windy conditions in the Southern Hemisphere keep cloud albedo high year-round. Our results have important implications for global-scale cloud feedbacks and contribute to efforts to develop a theory for planetary albedo and its symmetry.

Restricted access
Kevin Boyd
,
Zhuo Wang
, and
John E. Walsh

Abstract

Polar lows (PLs) are intense maritime mesocyclones that typically develop during marine cold-air outbreak events over the high latitudes. The impacts posed by these systems to humans and the broader environment demand a robust understanding of the environmental factors that promote PL formation and, in turn, skillful prediction of PL activity. We hypothesize that the variability of PL activity is associated with some key large-scale climate variables skewed toward “extreme” values, which can provide predictable information on PL activity beyond the synoptic time scale. A PL genesis potential index (PGI) is developed that relates the climatological spatial distribution of PL genesis frequency and key climate variables in a Poisson regression framework. The optimal set of predictors consists of a static stability parameter and an environmental baroclinicity parameter. The optimal predictor categories are shown to be robust across different reanalyses and PL track datasets. The observed spatial distribution and seasonal cycle of PL genesis frequency are represented well by the PGI, and the interannual variability of PL activity is captured skillfully. The effects of the Arctic Oscillation (AO), El Niño–Southern Oscillation (ENSO), and a few other climate modes on the interannual variability of PL activity are explored. Overall, our results suggest that the PGI may be used to inform skillful subseasonal to seasonal prediction of PL activity.

Significance Statement

Polar lows are intense mesocyclones over high-latitude oceans, and they have destructive impacts on coastal and island communities, and maritime and air operations. However, skillful prediction of polar lows on the subseasonal and longer time scales remains challenging. This study links polar low activity to large-scale environmental conditions in the Arctic through a statistical modeling approach. This work is based on the hypothesis that a shared statistical relationship exists between the large-scale climate variables and polar low activity across the Arctic, which enables a geographical unification of the controlling factors on polar low activity. Our results reveal two dominant factors, one related to the lower-tropospheric stratification and the other to the hydrodynamic instability of the lower-tropospheric flow. This statistical framework has potential applications to climate prediction and projection of polar low activity.

Restricted access
Richard M. Schulte
,
Christian D. Kummerow
,
Stephen M. Saleeby
, and
Gerald G. Mace

Abstract

There are many sources of uncertainty in satellite precipitation retrievals of warm rain. In this paper, the second of a two-part study, we focus on uncertainties related to spatial heterogeneity and surface clutter. A cloud resolving model simulation of warm, shallow clouds is used to simulate satellite observations from 3 theoretical satellite architectures – one similar to the Global Precipitation Measurement Core Observatory, one similar to CloudSat, and one similar to the planned Atmosphere Observing System (AOS). Rain rates are then retrieved using a common optimal estimation framework. For this case, retrieval biases due to nonuniform beam filling are quite large, with retrieved rain rates biased low by as much as 40-50% (depending on satellite architecture) at 5 km horizontal resolution. Surface clutter also acts to negatively bias retrieved rain rates. Combining all sources of uncertainty, the theoretical AOS satellite is found to outperform CloudSat in terms of retrieved surface rain rate, with a bias of −19% compared to −28%, a reduced spread of retrieval errors, and an additional 17.5 % of cases falling within desired uncertainty limits. The results speak to the need for additional high resolution modeling simulations of warm rain in order to better characterize the uncertainties in satellite precipitation retrievals.

Restricted access
Rong Fei
and
Yuqing Wang

Abstract

Recent studies have demonstrated the sensitivity of simulated tropical cyclone (TC) intensity to horizontal diffusion in numerical models. It is unclear whether such sensitivity comes from the horizontal diffusion in or above the boundary layer. To address this issue, both an Ooyama-type model and a full-physics model are used to conduct sensitivity experiments with reduced or enlarged horizontal mixing length (lh ) in the boundary layer and/or in the free atmosphere. Results from both models show that enlarging (reducing) lh throughout the model domain considerably reduces (increases) the TC intensification rate and quasi-steady intensity. A new finding is that changing lh above the boundary layer imposes a much greater influence than that in the boundary layer. Large lh above the boundary layer is found to effectively reduce the radial gradient of tangential wind inside the radius of maximum tangential wind and thus the inward flux of absolute vorticity, reducing the positive tangential wind tendency and the TC intensification rate and the steady-state intensity. In contrast, although larger lh in the boundary layer reduces the boundary-layer tangential wind tendency, it also leads to the more inward-penetrated inflow and thus enhances the inward flux of absolute vorticity, which offsets part of the direct negative contribution by horizontal diffusion, making the net change in tangential wind tendency not obvious. Results from three-dimensional simulations also show that the resolved eddies contribute negatively to TC spinup when lh is small, while its effect weakens when lh is enhanced either in or above the boundary layer.

Restricted access
Neelesh Rampal
,
Andrew Lorrey
, and
Nicolas Fauchereau

Abstract

Weather regimes (WRs), also known as synoptic types, are defined as recurrent patterns that have been used to categorize variability in atmospheric circulation. However, defining the optimal number of patterns can often be arbitrary, and there are common shortcomings when oversimplifying a wide range of synoptic conditions and weather outcomes. We build on previous work that has defined regional WRs and objectively ascribe an optimal number of once-daily weather patterns for Aotearoa New Zealand (ANZ) using affinity propagation combined with K-means clustering. Nine primary WRs for ANZ were classified based on once-daily geopotential height spatial patterns, but these patterns still retained a wide degree of spatial variability. Subsidiary clusters were subsequently defined within each primary WR by applying affinity propagation and K-means clustering to reveal the largest within-cluster differences based on joint daily temperature and precipitation anomalies. Up to three subsidiary patterns in each of the primary regimes were revealed, with a total of 21 unique daily patterns emerging from the two-tier classification. Subsidiary WRs reveal subtle differences in the location and intensity of regional-scale pressure anomalies, pressure gradients, and wind flow over both main islands that lead to large differences in surface weather anomalies. Impacts of atmospheric variability related to each subsidiary WR are exemplified by different spatial outcomes for rainfall and temperature (including intensity of anomalies) at regional and subregional levels. The approach presented in this study has utility for enhancing prediction of weather outcomes, including extreme weather, and can also be applied more widely over a range of time scales to improve understanding of weather and climate linkages.

Open access
Rolando R. Garcia

Abstract

Temperature observations made by the SABER infrared radiometer from January 2002 through December 2021 are used to study the structure and variability of the migrating diurnal temperature tide in the middle atmosphere (~17 to 105 km). In the lower stratosphere, and in the mesosphere and lower thermosphere (MLT), tidal structure is dominated by the gravest latitudinally symmetric mode, with a smaller contribution from the first anti-symmetric mode; in the middle and upper stratosphere, non-vertically propagating modes are prominent. Consistent with previous work, low-frequency variability is mainly semiannual, with maxima at the equinoxes. Quasi-biennial variability is also present and evident in low-passed time series. There are robust relationships between the semiannual and quasi-biennial variability of the tide and the semiannual and quasi-biennial tropical zonal wind oscillations, respectively, which persist throughout the 20-year dataset. While the physical mechanisms responsible for these relationships cannot be ascertained from the observations, the present results should be useful for hypothesis testing with numerical models. It is also found that the diurnal tide breaks due to convective instability in the MLT. This is reflected in its mean vertical structure, which grows as expected for a non-dissipating wave below ~85 km, but ceases to grow at higher altitudes. Direct confirmation that dissipation is due to breaking is obtained from the potential temperature field, which shows frequent instances of reversed vertical gradient, particularly at the equinoxes. Breaking of the diurnal tide has a major impact on the zonal-mean temperature and zonal wind structure of the MLT at the equinoxes.

Restricted access
Jingyi Chen
,
Samson Hagos
,
Zhe Feng
,
Jerome D. Fast
, and
Heng Xiao

Abstract

Some of the climate research puzzles relate to a limited understanding of the critical factors governing the the lifecycle of cumulus clouds. These factors force the initiation and the various mixing processes during cloud lifecycles. To shed some light into these processes, we tracked the lifecycle of thousands of individual shallow cumulus clouds in a large-eddy simulation during the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems field campaign in the U.S. Southern Great Plains. Concurrent evolution of clouds is tracked and their respective neighboring clouds are examined. Results show that the clouds initially smaller than neighboring clouds can grow larger than the neighboring clouds by a factor of 2 within 20% of their lifetime. Two groups of the tracked clouds with growing and decaying neighboring clouds, respectively, show distinct characteristics in their lifecycles. Clouds with growing neighboring clouds form above regions with larger surface heterogeneity, while clouds with decaying neighboring clouds are associated with less heterogeneous surfaces. Also, those with decaying neighboring clouds experience larger instability and a more humid boundary layer, indicating evaporation below the cloud-base is likely occurring before those clouds are formed. Larger instability leads to higher vertical velocity and convergence within the cloud, which causes stronger surrounding downdrafts and water vapor removal in the surrounding area. The latter appears to be the reason for the decaying neighboring clouds. Understanding those processes provide insights into how cloud-cloud interactions modulate the evolution of cloud population and into how this evolution can be represented in future cumulus parameterizations.

Restricted access
Sem Vijverberg
,
Raed Hamed
, and
Dim Coumou

Abstract

Soy harvest failure events can severely impact farmers, insurance companies and raise global prices. Reliable seasonal forecasts of mis-harvests would allow stakeholders to prepare and take appropriate early action. However, especially for farmers, the reliability and lead-time of current prediction systems provide insufficient information to justify within-season adaptation measures. Recent innovations increased our ability to generate reliable statistical seasonal forecasts. Here, we combine these innovations to predict the 1-3 poor soy harvest years in eastern US. We first use a clustering algorithm to spatially aggregate crop producing regions within the eastern US that are particularly sensitive to hot-dry weather conditions. Next, we use observational climate variables (sea surface temperature (SST) and soil moisture) to extract precursor timeseries at multiple lags. This allows the machine learning model to learn the low-frequency evolution, which carries important information for predictability. A selection based on causal inference allows for physically interpretable precursors. We show that the robust selected predictors are associated with the evolution of the horseshoe Pacific SST pattern, in line with previous research. We use the state of the horseshoe Pacific to identify years with enhanced predictability. We achieve very high forecast skill of poor harvests events, even 3 months prior to sowing, using a strict one-step-ahead train-test splitting. Over the last 25 years, 82% of the in February predicted poor harvests were correct. When operational, this forecast would enable farmers (and insurance/trading companies) to make informed decisions on adaption measures, e.g., selecting more drought-resistant cultivars, invest in insurance, change planting management.

Free access
Rasmus Wiuff

Abstract

In October 1941, Nazi Germany’s High Command realized that the war against the Soviet Union could not be ended before winter. The German professor Franz Baur prepared a long-range weather forecast for the winter of 1941/42. Baur never revealed anything about this forecast. However, according to an article published ten years after Baur’s death, Baur predicted that the winter of 1941/42 would be normal or milder than normal, primarily based on the main argument that the previous two winters had been very severe and never in climatic history had more than two severe winters occurred in a row. The winter ended up being one of the worst.

Today, Baur’s prognoses from wartime are public. In this article, it is shown that the previous description of Baur’s prognosis for the winter of 1941/42 is incorrect. Baur had a problematic relationship with his colleagues, so it is possible that the story of his prognosis is incorrect due to personal and professional contradictions. Baur’s postulated prognosis for the winter of 1941/42 destroyed his reputation. Based on the original prognoses from wartime and Baur’s scientific and personal history, this article shows that this judgment was too harsh and unfair.

Full access
Lauren Vorhees
,
Jane Harrison
,
Michael O’Driscoll
,
Charles Humphrey Jr.
, and
Jared Bowden

Abstract

Nearly one-half of the residents of North and South Carolina use decentralized or onsite wastewater treatment systems (OWTS). As the climate changes, coastal communities relying on OWTS are particularly vulnerable, as soil-based wastewater treatment may be reduced by water inundation from storm surge, sea level rise and associated groundwater rise, and heavy rainfall. Despite the vulnerabilities of OWTS to increased precipitation and sea level rise, there is little known about how onsite wastewater managers are responding to current and future climate risks. We conducted interviews with wastewater operators and installers and health regulators to understand the functioning, management, and regulation of OWTS in the current climate, challenges with rising sea levels and increases in extreme weather events, and what adaptation strategies could be implemented to mitigate negative impacts. Our results indicate that heavy precipitation and storm surges cause malfunctions for conventional septic systems where traditional site variables (e.g., soil type or groundwater level) are undesirable. Weather and climate are not required regulatory factors to consider in system selection and site approval, but many OWTS managers are aware of their impacts on the functioning of systems, and some are preemptively taking action to mitigate those impacts. Our findings suggest that filling gaps in the current communication structure between regulators and homeowners relying on OWTS is critical for coastal communities in the Carolinas to build climate resilience into decentralized wastewater infrastructure.

Significance Statement

This research aims to understand the functioning, management, and regulation of onsite wastewater treatment systems in the current climate, the challenges to these systems caused by rising sea levels and increases in extreme weather events, and the adaptation strategies that can be implemented to mitigate negative climate impacts. These results can be used by state government agencies, municipalities, and private sector wastewater managers to improve the resiliency of onsite wastewater treatment systems.

Restricted access