The dazzling lights of the aurora are created when high-energy particles from space collide with Earth’s atmosphere. While scientists have long understood this process, one big mystery remained: What powers the electric fields that accelerate these particles in the first place?
The dazzling lights of the aurora, Photo source: Screenshot of the Netflix TV series 𝐶𝑎𝑛 𝑇ℎ𝑖𝑠 𝐿𝑜𝑣𝑒 𝐵𝑒 𝑇𝑟𝑎𝑛𝑠𝑙𝑎𝑡𝑒𝑑?
A new study co-led by the Department of Earth and Planetary Sciences at The University of Hong Kong (HKU) and the Department of Atmospheric and Oceanic Sciences at the University of California, Los Angeles (UCLA) now provided an answer. Published in Nature Communications, the research reveals that Alfvén waves — plasma waves travelling along Earth’s magnetic field lines — act like an invisible power source, fueling the stunning auroral displays we see in the sky.
By analysing how charged particles move and gain energy in different regions of space, the researchers demonstrated that these waves act as a natural accelerator, supplying energy that drives charged particles down into the atmosphere and produces the glowing auroral lights.
To confirm their findings, the team analysed data collected by multiple satellites orbiting Earth, including NASA's Van Allen Probes and the THEMIS mission. The data provided solid evidence that Alfvén waves continuously transfer energy to the auroral acceleration region, maintaining the electric fields that would otherwise dissipate.
“This discovery not only provides a definitive answer to the physics of Earth’s aurora, but also offers a universal model applicable to other planets in our solar system and beyond,” said Professor Zhonghua YAO of the Department of Earth and Planetary Sciences at HKU. Professor Yao leads a dedicated team in space and planetary science at HKU, which has established a reputation for high-impact research on planetary auroras.
With deep expertise in the magnetospheric dynamics of planets like Jupiter and Saturn, the HKU team brought a critical planetary perspective to the study. “Our team at HKU has long focused on the auroral processes of giant planets. By applying this knowledge to the high-resolution data available near Earth, we have bridged the gap between Earth science and planetary exploration.” Professor Yao added.
The research represents a model of interdisciplinary collaboration. The UCLA team, led by Dr Sheng TIAN, contributed extensive expertise in Earth’s auroral physics, while the HKU team provided the broader context of planetary space physics.
HKU and UCLA Scientists Uncover the Mechanism powering “Space Battery” above Auroral Regions, Photo source; HKU
The full research paper can be read at: https://www.nature.com/articles/s41467-025-65819-4
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May
The Food and Environmental Hygiene Department (FEHD) today (May 21) released the fourth batch of gravidtrap indexes and density indexes for Aedes albopictus in May, covering 12 survey areas, as follows:
District |
Survey Area |
May 2026 |
First Phase Gravidtrap Index |
First Phase Density Index |
Eastern |
Shau Kei Wan and Sai Wan Ho |
9.1% |
1.4 |
Islands |
Tung Chung |
2.0% |
1.0 |
Kowloon City |
Hung Hom and To Kwa Wan |
6.7% |
1.5 |
Tai Po |
Tai Po East |
2.2% |
2.0 |
Tai Po West |
15.5% |
1.0 |
Tuen Mun |
Tuen Mun South |
9.1% |
1.4 |
District |
Survey Area |
May 2026 |
Area Gravidtrap Index |
Area Density Index |
Central and Western |
Kennedy Town and Shek Tong Tsui |
16.8% |
1.3 |
Eastern |
Chai Wan |
15.4% |
1.0 |
North Point and Quarry Bay |
18.9% |
1.4 |
Southern |
Aberdeen and Ap Lei Chau |
20.8% |
1.7 |
Sha Tin |
Sha Tin Town Centre and Fo Tan |
18.3% |
1.4 |
Tsuen Wan |
Tsuen Wan Town |
6.9% |
2.3 |
The fourth batch of gravidtrap indexes for Aedes albopictus in May includes First Phase Gravidtrap Indexes covering six survey areas and Area Gravidtrap Indexes covering six survey areas. Among which, six survey areas recorded gravidtrap indexes above 10 per cent, while Aberdeen and Ap Lei Chau in Southern District recorded a gravidtrap index above 20 per cent. Meanwhile, the gravidtrap indexes of six survey areas, namely Kennedy Town and Shek Tong Tsui in Central and Western District; North Point and Quarry Bay in Eastern District; Shau Kei Wan and Sai Wan Ho in Eastern District; Aberdeen and Ap Lei Chau in Southern District; Tai Po East in Tai Po District; and Tuen Mun South in Tuen Mun District, have recorded a decrease as compared to the indexes recorded in the last survey period, reflecting the progress of relevant mosquito control work.
With reference to the data from the past few years, the gravidtrap indexes start to rise from April or May every year. The actual timing and extent of the rise are affected by factors like weather conditions and rainfall. The average temperature and rainfall recorded in April this year were higher than those in the same period last year, creating favourable conditions for mosquito growth and breeding. As a result, the rise in gravidtrap indexes occurred earlier this year. With the increase in rainfall in May, the gravidtrap indexes are expected to rise further.
For survey areas which recorded indexes exceeding 10 per cent, in accordance with the mechanism implemented by the FEHD in response to the chikungunya fever (CF) situation (i.e. strengthening mosquito control work in areas with a gravidtrap index between 10 per cent and 20 per cent, instead of 20 per cent or above under the original mechanism), the FEHD is collaborating with relevant departments and stakeholders to identify locations with high mosquito infestations and carry out intensive and targeted mosquito control measures. The FEHD has initiated two prosecutions against the relevant construction site contractors following the discovery of mosquito breeding at construction sites in Tai Po District and Southern District. Moreover, following the discovery of stagnant water or stagnant water containers in a park, a construction site, a private housing estate, a clinic and a private premises in Tai Po District, Central and Western District, as well as Southern District, the FEHD has issued five statutory notices to the responsible persons-in-charge, requiring the clearance of such items within a specified timeframe. The FEHD, the relevant departments and stakeholders are following up on the mosquito control work, and will also organise exhibitions, distribute leaflets and posters, and notify residential estates that have subscribed to the gravidtrap Rapid Alert System, advising property management agents and residents to stay vigilant and work together in taking mosquito prevention and elimination measures. In addition, the FEHD will strengthen the monitoring of the gravidtrap index in the areas to review the effectiveness of the mosquito control work.
Public participation is crucial to the effective control of mosquito problems. The FEHD appeals to members of the public to continue to work together in strengthening personal mosquito control measures, including:
tidy up their premises and check for any accumulation of water inside the premises;
remove all unnecessary water collections and eliminate the sources;
check household items (those placed in outdoor and open areas in particular), such as refuse containers, vases, air conditioner drip trays, and laundry racks to prevent stagnant water;
change water in flower vases and scrub their inner surfaces thoroughly, and remove water in saucers under potted plants at least once a week;
properly cover all containers that hold water to prevent mosquitoes from accessing the water;
properly dispose of articles that can contain water, such as disposable meal boxes and empty cans; and
scrub drains and surface sewers with alkaline detergent at least once a week to remove any mosquito eggs.
Starting in August 2025, following the completion of the surveillance of individual survey areas, and once the latest gravidtrap index and the density index are available, the FEHD has been disseminating relevant information through press releases, its website and social media. It aims to allow members of the public to quickly grasp the mosquito infestation situation and strengthen mosquito control efforts, thereby reducing the risk of CF transmission.
Following recommendations from the World Health Organization and taking into account the local situation in Hong Kong, the FEHD sets up gravidtraps in districts where mosquito-borne diseases have been recorded in the past, as well as in densely populated places such as housing estates, hospitals and schools to monitor the breeding and distribution of Aedes albopictus mosquitoes, which can transmit CF and dengue fever. At present, the FEHD has set up gravidtraps in 62 survey areas of the community, with a surveillance period of two weeks. During the surveillance period, the FEHD will collect the gravidtraps once a week. After the first week of surveillance, the FEHD will immediately examine the glue boards inside the retrieved gravidtraps for the presence of adult Aedine mosquitoes to compile the Gravidtrap Index (First Phase) and Density Index (First Phase). At the end of the second week of surveillance, the FEHD will instantly check the glue boards for the presence of adult Aedine mosquitoes. Data from the two weeks of surveillance will be combined to obtain the Area Gravidtrap Index and the Area Density Index. The gravidtrap and density indexes for Aedes albopictus in different survey areas, as well as information on mosquito prevention and control measures, are available on the department's webpage (www.fehd.gov.hk/english/pestcontrol/dengue_fever/Dengue_Fever_Gravidtrap_Index_Update.html#).
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May Source: HKSAR Government Press Releases
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May Source: HKSAR Government Press Releases
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May Source: HKSAR Government Press Releases
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May Source: HKSAR Government Press Releases
FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May Source: HKSAR Government Press Releases
