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

Maximum Amplitude ◽

Longwave Radiation ◽

The Philippines ◽

Boreal Summer ◽

Monsoon Winds ◽

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.

Intraseasonal Variability of the Diurnal Cycle of Precipitation in the Philippines

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0152.1 ◽

2019 ◽

Vol 76 (11) ◽

pp. 3633-3654 ◽

Cited By ~ 2

Author(s):

Michael B. Natoli ◽

Eric D. Maloney

Keyword(s):

Diurnal Cycle ◽

Coastal Waters ◽

Sea Breeze ◽

Active Phase ◽

The Philippines ◽

Boreal Summer ◽

Breeze Circulation ◽

Convective Envelope ◽

Cycle Amplitude

Abstract Precipitation in the region surrounding the South China Sea over land and coastal waters exhibits a strong diurnal cycle associated with a land–sea temperature contrast that drives a sea-breeze circulation. The boreal summer intraseasonal oscillation (BSISO) is an important modulator of diurnal precipitation patterns, an understanding of which is a primary goal of the field campaign Propagation of Intraseasonal Tropical Oscillations (PISTON). Using 21 years of CMORPH precipitation for Luzon Island in the northern Philippines, it is shown that the diurnal cycle amplitude is generally maximized over land roughly 1 week before the arrival of the broader oceanic convective envelope associated with the BSISO. A strong diurnal cycle in coastal waters is observed in the transition from the inactive to active phase, associated with offshore propagation of the diurnal cycle. The diurnal cycle amplitude is in phase with daily mean precipitation over Mindanao but is nearly out of phase over Luzon. The BSISO influence on the diurnal cycle on the eastern side of topography is nearly opposite to that on the western side. Using wind, moisture, and radiation products from the ERA5 reanalysis, it is proposed that the enhanced diurnal cycle west of the mountains during BSISO suppressed phases is related to increased insolation and weaker prevailing onshore winds that promote a stronger sea-breeze circulation when compared with the May–October mean state. Offshore propagation is suppressed until ambient midlevel moisture increases over the surrounding oceans during the transition to the active BSISO phase. In BSISO enhanced phases, strong low-level winds and increased cloudiness suppress the sea-breeze circulation.

Impact of the Boreal Summer Intraseasonal Oscillation on the Diurnal Cycle of Precipitation near and over the Island of Luzon

Monthly Weather Review ◽

10.1175/mwr-d-19-0252.1 ◽

2020 ◽

Vol 148 (5) ◽

pp. 1805-1827

Author(s):

Kyle Chudler ◽

Weixin Xu ◽

Steven A. Rutledge

Keyword(s):

Intraseasonal Variability ◽

Vertical Wind Shear ◽

The Philippines ◽

Heat Fluxes ◽

Boreal Summer ◽

Diurnal Variability ◽

Boreal Summer Intraseasonal Oscillation ◽

Precipitation Estimates ◽

Monsoon Winds

Abstract During the boreal summer, satellite-based precipitation estimates indicate a distinct maximum in rainfall off the west coast of the island of Luzon in the Philippines. Also occurring during the summer months is the boreal summer intraseasonal oscillation (BSISO), a main driver of intraseasonal variability in the region. This study investigates the diurnal variability of convective intensity, morphology, and precipitation coverage offshore and over the island of Luzon. The results are then composited by BSISO activity. Results of this study indicate that offshore precipitation is markedly increased during active BSISO phases, when strong low-level southwesterly monsoon winds bring increased moisture and enhanced convergence upwind of the island’s high terrain. A key finding of this work is the existence of an afternoon maximum in convection over Luzon even during active BSISO phases, when solar heating and instability are apparently reduced due to enhanced cloud cover. This result is important, as previous studies have shown in other areas of the tropics afternoon convection over landmasses is a key component to offshore precipitation. Although offshore precipitation is maximized in the evening hours during active phases, results indicate that precipitation frequently occurs over the ocean around the clock (both as organized systems and isolated, shallow showers), possibly owing to an increase in sensible and latent heat fluxes, vertical wind shear, and convergence of the monsoon flow with land features.

Topographic Effects on the Luzon Diurnal Cycle during the BSISO

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0046.1 ◽

2019 ◽

Vol 77 (1) ◽

pp. 3-30 ◽

Cited By ~ 3

Author(s):

Emily M. Riley Dellaripa ◽

Eric D. Maloney ◽

Benjamin A. Toms ◽

Stephen M. Saleeby ◽

Susan C. van den Heever

Keyword(s):

South China Sea ◽

Diurnal Cycle ◽

Large Scale ◽

Boreal Summer ◽

Topographic Effects ◽

Surface Precipitation ◽

Amplitude Increase ◽

The Mean ◽

Induced Changes

Abstract Cloud-resolving simulations are used to evaluate the importance of topography to the diurnal cycle (DC) of precipitation (DCP) over Luzon, Philippines, and surrounding ocean during the July–August 2016 boreal summer intraseasonal oscillation (BSISO) event. Composites of surface precipitation for each 30-min time increment during the day are made to determine the mean DCP. The mean DCP is computed separately for suppressed and active BSISO conditions and compared across three simulations with varying topography—flat, true, and doubled topographic height. The magnitude of the topographic height helps to dictate the timing, intensity, and location of diurnal precipitation over and near Luzon. For example, the mean DCP in the true topography run peaks 1.5 h later, is broader by 1 h, and has a 9% larger amplitude during active conditions relative to suppressed conditions. By contrast, the flat run mean DCP is earlier and narrower by 0.5 h with a 5% smaller amplitude during active conditions versus suppressed conditions. Within the suppressed or active BSISO conditions, the mean DCP peak and amplitude increase as the topographic height increases. The presence of elevated topography focuses precipitation over the coastal mountains during suppressed conditions, while dictating which side of the domain (i.e., east Luzon and the Philippine Sea vs west Luzon and the South China Sea) more precipitation occurs in during active conditions. These topographic-induced changes are discussed in terms of mechanical and thermodynamic forcing differences between the two large-scale BSISO regimes for the three runs.

Impact of the Extended Boreal Summer Intraseasonal Oscillation on Western North Pacific Tropical Cloud Cluster Genesis Productivity

Journal of Climate ◽

10.1175/jcli-d-18-0113.1 ◽

2018 ◽

Vol 31 (22) ◽

pp. 9175-9191 ◽

Cited By ~ 5

Author(s):

Haikun Zhao ◽

Shaohua Chen ◽

Philip J. Klotzbach ◽

G. B. Raga

Keyword(s):

Relative Humidity ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Boreal Summer ◽

Synoptic Scale ◽

Boreal Summer Intraseasonal Oscillation ◽

Low Level ◽

Tropical cloud clusters (TCCs) are traditionally viewed as precursors of tropical cyclone (TC) genesis. Most studies have focused on the impact of the extended boreal summer intraseasonal oscillation (ISO) on TC activity over the western North Pacific (WNP), while the modulation of the ISO on WNP TCC genesis productivity (TCCGP), that is, the ratio of TC to TCC counts, has been investigated much less frequently. This study suggests that the extended boreal summer ISO modulates WNP TCCGP, with higher (lower) TCCGP during convectively active (inactive) ISO phases. Changes in TCCGP are found to be closely associated with changes of large-scale environmental factors. During the convectively active ISO phase, significantly increased TCCGP is associated with strengthened low-level cyclonic circulation anomalies and increased midlevel relative humidity anomalies over the WNP basin. The genesis potential index (GPI) contains several large-scale environmental variables demonstrated to relate to TCs and TCCs. The GPI can adequately depict the ISO modulation of WNP TCCGP through its alterations of large-scale parameters. Low-level vorticity makes the largest contribution to the change of TCCGP with a secondary contribution from midlevel relative humidity. Interestingly, the nonlinear GPI terms make comparable contributions, which can be partly explained by the synoptic-scale wave activity associated with the ISO mode. Stronger (weaker) 3–8-day synoptic-scale wave train intensity and increased (decreased) low-level eddy kinetic energy are found to be associated with the enhanced (weakened) monsoon circulation over the WNP basin during convectively active (inactive) ISO phases.

Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer

Atmosphere ◽

10.3390/atmos12020136 ◽

2021 ◽

Vol 12 (2) ◽

pp. 136

Author(s):

Yahya Darmawan ◽

Huang-Hsiung Hsu ◽

Jia-Yuh Yu

Keyword(s):

Large Scale ◽

Precipitation Variability ◽

Specific Humidity ◽

Boreal Summer ◽

Moisture Budget ◽

Large Scale Circulation ◽

Budget Analysis ◽

Sumatra Island ◽

Precipitation Anomalies ◽

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

The Impact of Finer-Resolution Air–Sea Coupling on the Intraseasonal Oscillation of the Indian Monsoon

Journal of Climate ◽

10.1175/2010jcli3868.1 ◽

2011 ◽

Vol 24 (10) ◽

pp. 2451-2468 ◽

Cited By ~ 38

Author(s):

Nicholas P. Klingaman ◽

Steven J. Woolnough ◽

Hilary Weller ◽

Julia M. Slingo

Keyword(s):

Atmospheric Stability ◽

Boreal Summer ◽

Upper Ocean ◽

Vertical Resolution ◽

Coupled Models ◽

Diurnal Variability ◽

Near Surface ◽

The Impact ◽

Coupling Frequency

Abstract A newly assembled atmosphere–ocean coupled model, called HadKPP, is described and then used to determine the effects of subdaily air–sea coupling and fine near-surface ocean vertical resolution on the representation of the Northern Hemisphere summer intraseasonal oscillation. HadKPP comprises the Hadley Centre atmospheric model coupled to the K-Profile Parameterization ocean boundary layer model. Four 30-member ensembles were performed that vary in ocean vertical resolution between 1 and 10 m and in coupling frequency between 3 and 24 h. The 10-m, 24-h ensemble exhibited roughly 60% of the observed 30–50-day variability in sea surface temperatures and rainfall and very weak northward propagation. Enhancing only the vertical resolution or only the coupling frequency produced modest improvements in variability and just a standing intraseasonal oscillation. Only the 1-m, 3-h configuration generated organized, northward-propagating convection similar to observations. Subdaily surface forcing produced stronger upper-ocean temperature anomalies in quadrature with anomalous convection, which likely affected lower-atmospheric stability ahead of the convection, causing propagation. Well-resolved air–sea coupling did not improve the eastward propagation of the boreal summer intraseasonal oscillation in this model. Upper-ocean vertical mixing and diurnal variability in coupled models must be improved to accurately resolve and simulate tropical subseasonal variability. In HadKPP, the mere presence of air–sea coupling was not sufficient to generate an intraseasonal oscillation resembling observations.

Disaster impacts in a port-city; learning from Beirut's Port explosion

10.5194/egusphere-egu21-14560 ◽

2021 ◽

Author(s):

Steluta topalov

Keyword(s):

Large Scale ◽

Focal Point ◽

Transportation System ◽

The Philippines ◽

Lessons Learned ◽

Social Dimension ◽

Global Network ◽

Port Cities ◽

Residential Units ◽

On 4 august 2020, one of the biggest non-nuclear explosions the world has seen in recent times took place in the Port of Beirut. Caused by the detonation of 2,750 tons of ammonium nitrate, inadequate stored in a warehouse in the port, the blast destroyed much of the city&#8217;s port and the surrounding infrastructure and severly&#160; damaged the dense residential and commercial areas within 5 km of the explosion site. The impact of the explosion, which registered as a 3.3 magnitude earthquake according to the U.S. Geological Survey, was felt as far away as the island of Cyprus.Athough the event was an technological hazard, the impact of the explosion is similar to a standardised natural disaster.According to UNDP, a total of 200 000 residential units were affected with an estimated of 40 000 buildings damaged; 200 people lost their lives, around 6 000 individuals were injuried and around 300 000 people were displaced.Such figure are comparable to other large-scale disasters such as Cyclone Vayu in India, which occured in June 2019 or the displacement caused by the Typhoon Vongfong, in the Philippines.The frequent increase of the natural disasters &#160;puts pressure on the critical infrastructure of the cities. The disruption of the transportation system, &#160;which is vital for the sustainable daily operations, are having a big impact on the economical, enviromental and social dimension of a city system. Among the various types of transportation system, ports are a focal point because of its strategic role for the economic growth of cities,regions and&#160; global network. In addition, they are nodal points for the social and economical activity of the inhabitants.Although the ports have played a key role in the development of their host cities, they are also vulnerable to a broad range of risks and threats because of a particular spatial character: the location at the intersection of land and sea. &#160;The study of the Beirut&#8217;s Port explosion examines the impact of port failures on the host urban enviroment and the relationship between hazards, vulnerability and the impact. The vulnerability of the port to disasters results &#160;to the vulnerability of its host city. A context &#8211;based understanding&#160; of the impact of the disaster and the elements at risk is essential to identify appropriate risk management strategies. The location of the port within the urban environment, in densely populated area, as in case of Beirut are some of the characteristics of the port cities that can magnify the impact of disasters to which they are prone. &#160;The study will focus on a collection of data that records the impact and allows visualisation of the complex patterns of the disaster risk reduction.The impact caused by the Beirut&#8217;s port explosion reminds us about the important role of the ports in their host cities and how fundamental is to identify the port&#8217;s infrastructure &#160;exposure to hazards and risks. &#160;Lessons learned from such event may be useful to reduce disaster risks in the port cities.

A Stochastic Parameter Perturbation Method to Represent Uncertainty in a Microphysics Scheme

Monthly Weather Review ◽

10.1175/mwr-d-20-0077.1 ◽

2021 ◽

Author(s):

Gregory Thompson ◽

Judith Berner ◽

Maria Frediani ◽

Jason A. Otkin ◽

Sarah M. Griffin

Keyword(s):

Land Surface ◽

Large Scale ◽

Random Perturbation ◽

Longwave Radiation ◽

Parameter Uncertainties ◽

Microphysics Scheme ◽

Convective Systems ◽

Temporal Correlations ◽

Precipitation Characteristics ◽

AbstractCurrent state-of-the art regional numerical weather forecasts are run at horizontal grid spacings of a few kilometers, which permits medium to large-scale convective systems to be represented explicitly in the model. With the convection parameterization no longer active, much uncertainty in the formulation of subgrid-scale processes moves to other areas such as the cloud microphysical, turbulence, and land-surface parameterizations. The goal of this study is to investigate experiments with stochastically-perturbed parameters (SPP) within a microphysics parameterization and the model’s horizontal diffusion coefficients. To estimate the “true” uncertainty due to parameter uncertainty, the magnitudes of the perturbations are chosen as realistic as possible and not with purposeful intent of maximal forecast impact as some prior work has done. Spatial inhomogeneities and temporal persistence are represented using a random perturbation pattern with spatial and temporal correlations. The impact on the distributions of various hydrometeors, precipitation characteristics, and solar/longwave radiation are quantified for a winter and summer case. In terms of upscale error growth, the impact is relatively small and consists primarily of triggering atmospheric instabilities in convectively unstable regions. In addition, small in situ changes with potentially large socio-economic impacts are observed in the precipitation characteristics such as maximum hail size. Albeit the impact of introducing physically-based parameter uncertainties within the bounds of aerosol uncertainties is small, their influence on the solar and longwave radiation balances may still have important implications for global model simulations of future climate scenarios.

A Precipitation-Based Index for Tropical Intraseasonal Oscillations

Journal of Climate ◽

10.1175/jcli-d-19-0019.1 ◽

2020 ◽

Vol 33 (3) ◽

pp. 805-823 ◽

Cited By ~ 1

Author(s):

Shuguang Wang

Keyword(s):

Real Time ◽

Decadal Variability ◽

Tropical Intraseasonal Oscillations

Longwave Radiation ◽

Boreal Summer ◽

Boreal Winter ◽

Eof Analysis ◽

Intraseasonal Oscillations ◽

Precipitation Anomalies ◽

AbstractCharacteristic patterns of precipitation-associated tropical intraseasonal oscillations, including the Madden–Julian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO), are identified using local empirical orthogonal function (EOF) analysis of the Tropical Rainfall Measuring Mission (TRMM) precipitation data as a function of the day of the year. The explained variances of the EOF analysis show two peaks across the year: one in the middle of the boreal winter corresponding to the MJO and the other in the middle of summer corresponding to the BSISO. Comparing the fractional variance indicates that the BSISO is more coherent than the MJO during the TRMM period. Similar EOF analyses with the outgoing longwave radiation (OLR) confirm this result and indicate that the BSISO is less coherent before the TRMM era (1979–98). In contrast, the MJO exhibits much less decadal variability. A precipitation-based index for tropical intraseasonal oscillation (PII) is derived by projecting bandpass-filtered precipitation anomalies to the two leading EOFs as a function of day of the year. A real-time version that approximates the PII is further developed using precipitation anomalies without any bandpass filtering. It is further shown that this real-time PII index may be used to diagnose precipitation in the subseasonal forecasts.

Relative Roles of Background Moisture and Vertical Shear in Regulating Interannual Variability of Boreal Summer Intraseasonal Oscillations

Journal of Climate ◽

10.1175/jcli-d-15-0498.1 ◽

2016 ◽

Vol 29 (19) ◽

pp. 7009-7025 ◽

Cited By ~ 11

Author(s):

Li Deng ◽

Tim Li

Keyword(s):

Interannual Variability ◽

Longwave Radiation ◽

Tropical Indian Ocean ◽

Atmospheric Model ◽

Vertical Shear ◽

Boreal Summer ◽

Moisture Condition ◽

Intensity Index ◽

Intraseasonal Oscillations

Abstract The interannual variability of the boreal summer intraseasonal oscillation (BSISO) is investigated using observed outgoing longwave radiation (OLR) and ERA-Interim data for the period of 1980–2012. It is found that the interannual variability of BSISO intensity is much stronger in the tropical western Pacific (TWP) than the tropical Indian Ocean (TIO). A BSISO intensity index is defined based on a multivariate EOF analysis in TWP. It is found that strong BSISO years are associated with El Niño–like sea surface temperature anomalies in the tropical Pacific, anomalous easterly shear, and enhanced background moisture condition in the region. Using a 2.5-layer atmospheric model with a specified idealized background mean state, the authors further examine the relative roles of background moisture and vertical shear fields in modulating the BSISO intensity. Sensitivity numerical experiments indicate that the background moisture change is most important in regulating the BSISO intensity, whereas the background vertical shear change also plays a role.