Christian Jakob

Christian Jakob
Monash University (Australia) · School of Geosciences, Clayton

PhD

About

187
Publications
21,881
Reads
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7,210
Citations
Additional affiliations
June 2007 - present
Monash University (Australia)
Position
  • Professor
January 2002 - May 2007
Bureau of Meteorology
Position
  • Researcher
October 1993 - December 2001
European Center For Medium Range Weather Forecasts
Position
  • Researcher

Publications

Publications (187)
Article
Focussing on the major cities of Brisbane, Sydney, and Melbourne in southeast Australia, this study seeks to determine the environmental factors that distinguish between heavy rainfall events (HREs) and extreme rainfall events (EREs). Using daily rain gauge observations, HREs and EREs are defined for each domain based, respectively, on the 95th and...
Article
A clustering methodology is applied to cloud optical depth cloud top pressure (TAU-PC) histograms from the new, 1-degree resolution, ISCCP-H dataset, to derive an updated global Weather State (WS) dataset. Then, PC-TAU histograms from current-climate CMIP6 model simulations are assigned to the ISCCP-H WSs along with their concurrent radiation and p...
Article
Climate models are fundamental to understanding climate change and anticipating its risks. They provide the basis for predicting impacts, guiding adaptation decisions and setting mitigation targets. Society now needs more detailed and precise information to enable robust decision-making in the face of rapidly amplifying climate change and for achie...
Article
A robust and computationally efficient object tracking algorithm is developed by incorporating various tracking techniques. Physical properties of the objects, such as brightness temperature or reflectivity, are not considered. Therefore, the algorithm is adaptable for tracking convection-like features in simulated data and remotely sensed two-dime...
Article
Full-text available
Abstract Small‐domain cloud‐resolving model and single‐column model simulations have historically applied one of three representations of large‐scale vertical motion, wLS. In simulations of radiative‐convective equilibrium, wLS=0, and a balance develops between convective heating and radiative cooling. Under the weak‐temperature gradient approximat...
Article
Full-text available
Plain Language Summary On horizontal scales of several tens to hundreds of kilometers, which we call “mesoscale,” mean vertical motion is very small compared to mean horizontal motion. Yet the vertical motion exerts a critical influence on the formation of clouds: Large‐scale descent is associated with fair weather, and ascent is associated with cl...
Article
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Precipitation efficiency refers to the fraction of condensate in the atmosphere that reaches the surface as precipitation. A high‐quality data set of radar‐estimated precipitation rates and convective scale vertical velocity near Darwin, Australia, is used to construct the first estimate of precipitation efficiency at convective scales for a long r...
Article
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Accurately representing the properties and impact of tropical convection in climate models requires an understanding of the relationships between the state of a convective cloud ensemble and the environment it is embedded in. We investigate this relationship using 13 years of radar observations in the tropics. Specifically, we focus on convective c...
Article
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A multiplicative cascade model called HiDRUS is developed, and tested in the greater Melbourne region (Australia) by downscaling coarse resolution ERA‐I rainfall to 1 km horizontal and 6 minute temporal resolutions. The parameters required for the cascade model are computed from radar observations of rain events during 2008–2015, and a library of r...
Article
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Future precipitation changes include contributions from both thermodynamic and dynamic processes. Given that precipitation in the tropics is commonly associated with convergence lines, we construct a simple linear regression model relating the convergence line frequency and strength to precipitation at subdaily time scales, and use it to show that...
Article
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...
Article
Full-text available
Global climate models suffer from a persistent shortcoming in their simulation of rainfall by producing too much drizzle and too little intense rain. This erroneous distribution of rainfall is a result of deficiencies in the representation of underlying processes of rainfall formation. In the real world, clouds are precursors to rainfall and the di...
Article
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Distributions of rainfall with the time and space resolutions of minutes and kilometers respectively are often needed to drive the hydrological models used in a range of engineering, environmental and urban design applications. The work described here is the first step in constructing a model capable of downscaling rainfall to scales of minutes and...
Article
Annual precipitation in north-western Australia has been increasing since the 1950s. The work presented here investigates the causes of rainfall using K-means clustering to classify daily rainfall patterns into regimes, demonstrating their link to known synoptic structures in northern Australia and explaining the overall change in rainfall in terms...
Article
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Recent research has suggested that the overall dependence of convection near coasts on large-scale atmospheric conditions is weaker than over the open ocean or inland areas. This is due to the fact that in coastal regions convection is often supported by meso-scale land-sea interactions and the topography of coastal areas. As these effects are not...
Article
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The parameterization of convection in climate models is a large source of uncertainty in projecting future precipitation changes. Here, an objective method to identify organized low-level convergence lines has been used to better understand how atmospheric convection is organized and projected to change, as low-level convergence plays an important...
Article
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Deep convection is a multiscale process that significantly influences the budgets of heat, moisture and momentum. In global climate models the thermodynamic effects of convection are normally treated by parametrisation schemes, with a separate formulation for convective momentum transport (CMT). The transport modules for current thermodynamic and m...
Article
The initiation of Northern Australian monsoon rainfall bursts is accompanied by an increase in cyclonic circulation in the monsoon region. In this study we show that the change in circulation at the start of the composite rainfall burst is predominantly influenced by mid-latitude front-like features. By exploiting the relationship between circulati...
Article
Full-text available
Previous work has shown that: the sharp fall in winter rainfall over coastal southwestern Australia in 1970s was mainly due to a fall in the frequency of fronts; the gradual reduction in rainfall since the late 1990s was due to a reduction in the number of light rain days; and the increased inland summer rainfall in the 1970s was due to an increase...
Article
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We implement a Stochastic Multicloud Model (SMCM) in an observation-informed configuration into the convection scheme of the state-of-the-art GCM ECHAM6.3. The SMCM configuration we use here has been tuned to represent observed tropical convection by associating the occurrence and strength of deep convection to mid-tropospheric vertical velocity an...
Article
Human activity is changing Earth's climate. Now that this has been acknowledged and accepted in international negotiations, climate research needs to define its next frontiers.
Conference Paper
Full-text available
This study examines commuter cyclist’s travel behaviour, particularly in response to changes in weather conditions and situational factors. Motivators, deterrents and preferences of commuter cycling are also examined. In an effort to reach greater understanding of a commuter cyclist’s decision making process, cyclists have been clustered. Disaggreg...
Article
Full-text available
This study examined commuter cyclists’ travel behavior, particularly in response to changes in weather conditions and situational factors. The motivators, deterrents, and preferences of commuter cycling were also examined. To reach greater understanding of commuter cyclists’ decision making, cyclists were clustered. Disaggregated travel data were c...
Article
Full-text available
Climate models show considerable rainfall biases in coastal tropical areas, where approx. 33% of the overall rainfall received is associated with coastal land-sea interaction. Building on an algorithm to objectively identify rainfall that is associated with land-sea interaction we investigate whether the relationship between rainfall in coastal reg...
Article
A climatology of clouds within marine cold air outbreaks, primarily using long-term satellite observations, is presented. Cloud properties between cold air outbreaks in different regions in both hemispheres are compared. In all regions marine cold air outbreak clouds tend to be low level with high cloud fraction and low-to-moderate optical thicknes...
Article
Cumulus parameterizations in general circulation models (GCMs) frequently apply mass-flux schemes in their description of tropical convection. Mass flux constitutes the product of the fractional area covered by cumulus clouds in a model grid box and the vertical velocity within the cumulus clouds. The cumulus area fraction profiles can be derived f...
Article
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A comparison of marine cold air outbreaks (MCAOs) in the Northern and Southern Hemispheres is presented, with attention to their seasonality, frequency of occurrence, and strength as measured by a cold air outbreak index. When considered on a gridpoint-by-gridpoint basis, MCAOs are more severe and more frequent in the Northern Hemisphere (NH) than...
Conference Paper
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An adequate representation of convective processes general circulation models (GCMs) remains one of the grand challenges in atmospheric science. In particular, the models struggle with correctly representing convection associated tropical intraseasonal variability. We use observations of tropical convection obtained from high resolution rain radar...
Conference Paper
This study examines commuter cyclist’s travel behavior specifically in response to changes in weather. In an effort to contribute to greater understanding of commuter cyclist’s decision making process the Theory of Planned Behaviour (TPB) is used to predict their intention to cycle and their actual cycling behavior. Disaggregate travel data collect...
Article
Much of the day-to-day variability of rainfall in the midlatitudes is controlled by the passage of extratropical cyclones and their related fronts. A good representation of fronts and their associated rainfall in climate models is essential to have confidence of future projections of midlatitude precipitation. An objective front identification meth...
Article
Full-text available
Rainfall in coastal areas of the tropics is often shaped by the presence of circulations directly associated with the topography, such as land-sea and/or mountain-valley breezes. In many regions the coastally-affected rainfall consitutes more than half of the overall rainfall received. Weather and climate models with parametrized convection produce...
Article
The linear trend in the local Hadley and Walker circulations from 1979 to 2009 is calculated. These local circulations are defined through a decomposition of the vertical mass flux into its zonal and meridional components. Defining the local circulation this way ensures that the two orthogonal circulations (the local Hadley and Walker circulations)...
Article
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A deficit of shortwave cloud forcing over the Southern Ocean is persistent in many global climate models. Cloud regimes have been widely used in model evaluation studies to make a process-oriented diagnosis of cloud parameterization errors, but cloud regimes have some limitations in resolving both observed and simulated cloud behavior. A hybrid met...
Conference Paper
Full-text available
An adequate representation of convective processes in numerical models of the atmospheric circulation (general circulation models, GCMs) remains one of the grand challenges in atmospheric science. In particular, the models struggle with correctly representing the spatial distribution and high variability of tropical convection. It is thought that t...
Article
Full-text available
Fundamental puzzles of climate science remain unsolved because of our limited understanding of how clouds, circulation and climate interact. One example is our inability to provide robust assessments of future global and regional climate changes. However, ongoing advances in our capacity to observe, simulate and conceptualize the climate system now...
Article
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Increasing global precipitation has been associated with a warming climate resulting from a strengthening of the hydrological cycle. This increase, however, is not spatially uniform. Observations and models have found that changes in rainfall show patterns characterized as 'wet-gets-wetter' and 'warmer-gets-wetter'. These changes in precipitation a...
Article
Cumulus parameterizations in weather and climate models frequently apply mass-flux schemes in their description of tropical convection. Mass flux constitutes the product of the fractional area covered by convection in a model grid box and the vertical velocity in cumulus clouds. However, vertical velocities are difficult to observe on GCM scales, m...
Article
Organized tropical convection is a crucial mechanism in the climate system but its representation in climate models through parametrization schemes has numerous shortcomings. One of these shortcomings is that they are deterministic despite the statistical nature of the relationship they are representing. Several attempts at devising a stochastic pa...
Article
Observational data of rainfall from a rain radar in Darwin, Australia, are combined with data defining the large-scale dynamic and thermodynamic state of the atmosphere around Darwin to develop a multicloud model based on a stochastic method using conditional Markov chains. The authors assign the radar data to clear sky, moderate congestus, strong...
Article
Full-text available
Coastally induced rainfall is a common feature especially in tropical and subtropical regions. However, it has been difficult to quantify the contribution of coastal rainfall features to the overall local rainfall. We develop a novel technique to objectively identify precipitation associated with land-sea interaction and apply it to satellite based...
Data
This repository contains source-code for the recognition of coastal rainfall project. A zip-file with the source-code can be retrieved below or from GitHub (https://github.com/antarcticrainforest/PatternRecog). A description of how to apply the algorithm is also available on GitHub. For scientific details, see the Journal of Climate publication "Gl...
Article
Climate models have increased in complexity over time as more processes have been included. Now we need to return to the underpinning basics in the models and ensure they are the best they can be.
Article
Atmospheric fronts are important for the day-to-day variability of weather in the midlatitudes. It is therefore vital to know how their distribution and frequency will change in a projected warmer climate. Here we apply an objective front identification method, based on a thermal front parameter, to 6-hourly data from models participating in CMIP5....
Article
Tropical precipitation is caused by many processes that occur over a wide-range of temporal and spatial scales. Such processes vary from local, diurnal convection driven by a destabilisation of the boundary layer to planetary-scale systems that result in rainfall over many days. It is therefore important to assess whether general circulation models...
Article
Full-text available
Since the 1970s, winter rainfall over coastal southwestern Australia (SWA) has decreased by 10%–20%, while summer rainfall has been increased by 40%–50% in the semiarid inland area. In this paper, a K-means algorithm is used to cluster rainfall patterns directly as opposed to the more conventional approach of clustering synoptic conditions (usually...
Conference Paper
Full-text available
An adequate representation of convective processes in numerical models of the atmospheric circulation remains one of the grand challenges in atmospheric science. In particular, the models struggle with correctly representing the spatial distribution and high variability of tropical convection. It is thought that this model deficiency partly results...
Article
The representation of clouds over the Southern Ocean in contemporary climate models remains a major challenge. A major dynamical influence on the structure of clouds is the passage of extratropical cyclones. They exert significant dynamical influences on the clouds in the dynamically active frontal regions as well as in the dynamically suppressed r...
Article
Full-text available
Clouds strongly affect the absorption and reflection of shortwave and longwave radiation in the atmosphere. A key bias in climate models is related to excess absorbed shortwave radiation in the high-latitude Southern Ocean. Model evaluation studies attribute these biases in part to midtopped clouds, and observations confirm significant midtopped cl...
Article
Four model intercomparisons were run and evaluated using the TWP-ICE field campaign, each involving different types of atmospheric model. Here we highlight what can be learnt from having single-column model (SCM), cloud-resolving model (CRM), global atmosphere model (GAM) and limited-area model (LAM) intercomparisons all based around the same field...
Article
The representation of rainfall and in particular its diurnal cycle, is generally poor in general circulation models (GCMs). Nonetheless, studies make use of GCMs in future climate projections in regions where precipitation has a strong diurnal cycle. In this study we evaluate whether one GCM (ACCESS1.3) can represent the rainfall in such a region (...
Article
Some cumulus clouds with tops between 3 and 7 km (Cu3km-7km) remain in this height region throughout their lifetime (congestus) while others develop into deeper clouds (cumulonimbus). This study describes two techniques to identify the congestus and cumulonimbus cloud types using data from scanning weather radar and identifies the atmospheric condi...
Article
Conceptually, it is useful to partition the three-dimensional tropical circulation into meridional and zonal components, na